Process for the preparation of 4-hydroxy-2-methylene-butanaldehyde, 4-hydroxy-2-methyl-butan-2-enaldehyde and their esters

Abstract

The present invention relates to a process for the preparation of 4-hydroxy-2-methylene-butyraldehyde, 4-hydroxy-2-methyl-but-2-enal and their esters of formulae (I.a) and (I.b), # imgabs0 wherein R1 is as defined in the claims and the description, R2 is as defined in the claims and the description, and R3 is as defined in the description, and to a process for the preparation of 4-hydroxy-2-methylene-butyraldehyde, 4-hydroxy-2-methyl-but-2-enal and their esters. The process is carried out by subjecting isoprenol or an ester thereof to photooxidation in the presence of a photosensitizer and optionally a transition metal catalyst, in which the reaction mixture obtained in the photooxidation is subsequently brought into contact with the transition metal catalyst in the absence of the transition metal catalyst. Furthermore, the invention relates to certain hydroperoxides of the compound (I.a) or (I.b); and to their use as intermediates in the synthesis of compounds (I.a) and (I.b) or in the synthesis of retinol, stereoisomers and derivatives thereof.

Description

[0001] The present invention relates to a process for preparing 4-hydroxy-2-methylene-butyraldehyde, 4-hydroxy-2-methyl-but-2-enal and / or their esters of formula Ia and Ib as defined below, by subjecting an isoprenol of formula II.a as defined below or its esters to photooxidation in the presence of a photosensitizer and optionally a transition metal catalyst, wherein, in the case of photooxidation in the absence of a transition metal catalyst, the reaction mixture obtained in the photooxidation is subsequently contacted with a transition metal catalyst. In addition, the present invention relates to the use of certain compounds of formula Ia or Ib as defined below as intermediates in the synthesis of retinol, its stereoisomers and derivatives, in particular esters; to certain hydroperoxides of formula III.a, III.b or III.c as defined below; and to their use as intermediates in the synthesis of compounds Ia and Ib or in the synthesis of retinol, its stereoisomers and derivatives, in particular esters. Background Art

[0002] 4-Acetoxy-2-methylbut-2-enal (its E isomer is also called C5 acetate), the acetate ester of the above-mentioned 4-hydroxy-2-methyl-but-2-enal, is an important building block in the industrial synthesis of retinol, its stereoisomers and derivatives. Acetoxy-2-methylbut-2-enal, for example in the form of its E-isomer C5 acetate, is currently obtained on an industrial scale from vinyl glycol-1,2-diacetate (VGDA), a by-product of industrial processes, via hydroformylation and deacetoxylation. The subsequent steps are described, for example, in DE 10117065 and the references cited therein.

[0003] However, the economic availability of VGDA depends on the unaltered continuation of the industrial processes from which it originates. Given that the lifespan of such processes is increasingly unpredictable, whether due to increasing raw material and energy costs, increasing ecological demands, or increasingly unreliable supply chains, it is desirable to have alternative pathways to C5 acetates, their isomers and derivatives on hand. Furthermore, the limited amount of VGDA available through the processes makes alternative pathways desirable.

[0004] Other known synthetic routes to C5 acetates are the oxidation of prenyl acetate with selenium dioxide as described, for example, in CN 108997112, the oxidation of benzyl isoprene ether as described, for example, in S. Inoue et al., Chemistry Lett. 1986, 2035-2038, the oxidation of isoprene chloride with oxygen as described, for example, in CN 108707076, the oxidation of isoprene as described, for example, in PA Wehrli et al., Synthesis, 1977, 649-650, the acetylation of prenyl alcohol and the oxidation of the resulting prenyl alcohol acetate with peroxide under irradiation in the presence of a photosensitizer as described in CN 110981724 A and the oxidation of prenyl alcohol acetate in an electrochemical process as described in CN 111270261 A. However, these routes are not suitable for application on an industrial scale.

[0005] 4-Acetoxy-2-methylbut-2-enal, basic alcohol 4-hydroxy-2-methyl-but-2-enal and other esters thereof can be obtained by known methods, for example via Pd-catalyzed C-C double bond isomerization as described, for example, in US 4,124,619 or CN 103467287, from the corresponding 2-methylene double bond isomers (i.e. from 3-formylbut-3-enyl acetate, 4-hydroxy-2-methylene-butyraldehyde or other esters thereof).

[0006] It is desirable to find an alternative route to 4-hydroxy-2-methyl-but-2-enal or 4-hydroxy-2-methylene-butyraldehyde and the esters of these alcohols; ideally, this route should be suitable for industrial scale. For environmental and economic reasons, this route, at least its essential steps, in particular should also operate with very small amounts of solvent; ideally pure, i.e. in the absence of solvent.

[0007] Isoprenol (3-methylbut-3-en-1-ol) is a bulk chemical readily available from isobutylene and formaldehyde. Isomerization of its double bond yields isoprenol (3-methylbut-2-en-1-ol). Its esters are available via standard esterification processes.

[0008] The photooxidation of olefins with singlet oxygen to allylic hydroperoxides (Schenckene reaction) followed by dehydration to α-enones has been described in the art.

[0009] ED Mihelich et al. describe the preparation of α-enones by reacting cycloolefins, methyl oleate and other olefinically unsaturated hydrocarbons with singlet oxygen in J. Org. Chem. 1983, 48, 4135-4137. For this purpose, oxygen is passed through a reaction mixture containing olefinically unsaturated hydrocarbons, acetic anhydride, pyridine, N,N-dimethylaminopyridine (DMAP) and tetraphenylporphyrin (TPP) as a photosensitizer in methylene chloride, and the reactants are simultaneously irradiated with a sodium vapor lamp.

[0010] H.-J. Liu et al. describe the synthesis of (+)-artemisinin in Tetrahedron Lett. 1993, 34 (28), 4435-4438. The synthesis covers in particular a step in which a tricyclic olefinically unsaturated carbocycle is converted into the corresponding α-enone by irradiation of a reaction mixture containing the unsaturated ring, acetic anhydride, pyridine, DMAP and TPP in methylene chloride through which oxygen is passed.

[0011] K. You et al. describe in Journal of Photochemistry and Photobiology A: Chemistry, 2011, 217, 321-325 the photosensitized oxidation of α-pinene, β-pinene and limonene to α-enones using sodium tetrachlorotetraiodofluorescein as a sensitizer in the presence or absence of lutidine and / or acetic anhydride in methanol or DMF as solvent.

[0012] P. Bayer et al., Green Chem., DOI: 10.1039 / d0gc00436g, describe the photooxidation of olefins to hydroperoxides with singlet oxygen in a solvent-free continuous flow reaction apparatus. The further conversion of unstable hydroperoxides to, for example, α-ene ketones is schematically described as the reaction of hydroperoxides with acetic anhydride and pyridine in dichloromethane.

[0013] EL Clennan et al. describe the photooxidation of various allylic alcohols with singlet oxygen in Photochemistry and Photobiology, 2006, 82, 1226-1232. In particular, isoprenol is converted to 3-methyl-but-2-enal, 3,3-dimethyloxirane-2-carbaldehyde, 2-hydroperoxy-3-methyl-but-3-en-1-ol and 5,5-dimethyl-1,2-dioxolane-3-ol in the presence of TPP in CDCl3.

[0014] The conversion of acyclic geminally disubstituted α-olefins into aldehydes via photooxidation and dehydration using transition metal catalysts has not been described in the prior art. Summary of the invention

[0015] The present inventors have found that 4-hydroxy-2-methyl-but-2-enal, 4-hydroxy-2-methylene-butyraldehyde and esters of these alcohols can be obtained by subjecting isoprene alcohol or its ester to photooxidation in the presence of a photosensitizer and a transition metal catalyst, or by subjecting isoprene alcohol or its ester to photooxidation in the presence of a photosensitizer and subsequently contacting the hydroperoxide formed in the photooxidation with a transition metal catalyst.

[0016] The present invention therefore relates to a process for preparing a compound of formula Ia or Ib or a mixture thereof, or a stereoisomer of a compound Ia or Ib, or a mixture of different stereoisomers of a compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib,

[0017]

[0018] in

[0019] R 1 is hydrogen or -C(=O)R 2 ;and

[0020] R 2 It is C1-C 20 -alkyl;

[0021] The method comprises:

[0022] (i) providing a reaction mixture comprising a compound of formula II.a, a photosensitizer and optionally a transition metal catalyst:

[0023]

[0024] Where R 1 As defined above;

[0025] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light;

[0026] (iii) contacting the reaction mixture of or obtained in step (ii) with a transition metal catalyst if a transition metal catalyst has not already been provided in step (i);

[0027] (iv.1) if desired, after completion of the reaction, isolating the one or more compounds Ia or Ib obtained in step (ii) or (iii); and

[0028] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R1 It is hydrogen;

[0029] or

[0030] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (ii) or (iii); and

[0031] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0032] Furthermore, the present invention relates to the use of a compound of formula Ia or Ib other than (E)-4-acetoxy-2-methylbut-2-enal as defined above, or a stereoisomer of compound Ia or Ib other than (E)-4-acetoxy-2-methylbut-2-enal, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, as an intermediate in the synthesis of retinol, its stereoisomers, its derivatives (wherein the derivatives are in particular its esters) or stereoisomers of its derivatives (wherein the derivatives are in particular its esters).

[0033] The invention also relates to a hydroperoxide compound of the formula III.a, III.b or III.c, or a stereoisomer of a compound of the formula III.a, III.b or III.c, or a mixture of different stereoisomers of compounds III.a, III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c,

[0034]

[0035] in

[0036] In compound III.a, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl;

[0037] In compound III.b, R 1 Yes-C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl; and

[0038] In compound III.c, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl;

[0039] Preferably it is a hydroperoxide compound of the formula III.a or III.b, or a stereoisomer of a compound of the formula III.a or III.b, or a mixture of different stereoisomers of compounds III.a and / or III.b, or a mixture of different compounds III.a and / or III.b

[0040]

[0041] and relates to the use of the hydroperoxides of formula III.a, III.b or III.c, or stereoisomers of compounds of formula III.a, III.b or III.c, or mixtures of different stereoisomers of compounds III.a and / or III.b and / or III.c, or mixtures of different compounds III.a, III.b and / or III.c, as defined above, wherein R 1 It can also be hydrogen, preferably the use of a hydroperoxide of the formula III.a or III.b as defined above, or a stereoisomer of a compound of the formula III.a or III.b, or a mixture of different stereoisomers of compounds III.a and / or III.b, or a mixture of different compounds III.a and / or III.b, wherein, however, in compound III.b R 1 It can also be hydrogen, which is used as an intermediate in the synthesis of a compound of formula Ia or Ib as defined above, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, or as an intermediate in the synthesis of retinol, its stereoisomers, its derivatives (wherein the derivatives are preferably its esters (i.e. retinol esters), retinal or retinoic acid, and in particular its esters) or stereoisomers of its derivatives (wherein the derivatives are preferably its esters (i.e. retinol esters), retinal or retinoic acid, and in particular its esters). DETAILED DESCRIPTION

[0042] definition

[0043] "Alkyl" is used in the usual sense. The term "alkyl" refers to a group having 1 or 2 carbon atoms ("C1-C2-alkyl"), 1 to 4 carbon atoms ("C1-C4-alkyl"), or 1 to 20 carbon atoms ("C1-C 20C1-C2-alkyl means a saturated straight-chain or branched aliphatic acyclic hydrocarbon radical having 1 or 2 carbon atoms. Examples are methyl and ethyl. C1-C4-alkyl means a saturated straight-chain or branched aliphatic acyclic hydrocarbon radical having 1 to 4 carbon atoms. Examples are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl and tert-butyl. C1-C 20 -Alkyl represents a saturated straight-chain or branched aliphatic acyclic hydrocarbon radical having 1 to 20 carbon atoms. Examples, in addition to those mentioned for C1-C4-alkyl, are n-pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, n-hexyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3 - dimethylbutyl, 1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl, 1-ethyl-2-methylpropyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl, 2-propylheptyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl, n-nonadecyl, n-eicosyl and their (other) structural isomers. 15 -Alkyl is CH3(CH2) 14 -.

[0044] Chlorinated C1-C2-alkanes are methane or ethane in which some or all of the hydrogen atoms are replaced by chlorine atoms. Examples are dichloromethane (methylene chloride), trichloromethane (chloroform), tetrachloromethane (carbon tetrachloride), 1,1-dichloroethane, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2-trichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane and pentachloroethane.

[0045] C2-C8-carboxylates are anions or salts of C2-C8-carboxylic acids. The anion can be described as RC(=O)O - , wherein R is C1-C7-alkyl. Examples are acetate, propionate, butyrate, etc.

[0046] The term "stereoisomer" as used in the context of the present invention relates to optical isomers, such as enantiomers or diastereomers, the latter existing due to more than one stereogenic center in a molecule, but in particular to Z / E isomers (due to the presence of correspondingly substituted double bonds or ring systems). Thus, the stereoisomers of compound Ib are mainly the E isomer (E)-Ib and the Z isomer (Z)-Ib:

[0047]

[0048] If the free radical R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group, such as sec-butyl, then optical isomers of compound Ib exist.

[0049] Similarly, the stereoisomers of compound III.b are mainly E isomer (E)-III.b and Z isomer (Z)-III.b:

[0050]

[0051] If the free radical R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group, such as sec-butyl, then the optical isomers of compound III.b exist.

[0052] Similarly, if the free radical R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group, such as sec-butyl, then the optical isomers of compound Ia exist; and if the free radical R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group, such as sec-butyl, then the optical isomers of compounds III.a and III.c exist.

[0053] The mixture of different stereoisomers of Compound Ib is mainly a mixture of E-isomers and Z-isomers, but may also be a mixture of enantiomers or diastereomers of Compound Ib, wherein R 1 Yes-C(=O)R 2 And R 2It is a C4-C with one or more stereogenic centers. 20 -alkyl group. Similarly, a mixture of different stereoisomers of compound III.b is primarily a mixture of E-isomers and Z-isomers, but may also be a mixture of enantiomers or diastereomers of compound III.b, wherein R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group. A mixture of different stereoisomers of compound Ia is a mixture of enantiomers or diastereomers of compound Ia, wherein R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group. Similarly, a mixture of different stereoisomers of compound III.a is a mixture of enantiomers or diastereomers of compound III.a, wherein R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group. Similarly, a mixture of different stereoisomers of compound III.c is a mixture of enantiomers or diastereomers of compound III.c, wherein R 1 Yes-C(=O)R 2 And R 2 It is a C4-C with one or more stereogenic centers. 20 -alkyl group.

[0054] The mixture of compounds Ia or Ib may be a mixture of two or more different compounds Ia, wherein the free radicals R 1 different; a mixture of two or more different compounds Ib, wherein the free radical R 1 Different; a mixture of compound Ia and compound Ib, wherein the free radical R in compound Ia and Ib 1 has the same meaning; a mixture of compound Ia and compound Ib, wherein the free radical R in compounds Ia and Ib 1has different meanings; a mixture of compound Ia with two or more different compounds Ib; a mixture of compound Ib with two or more different compounds Ia; or a mixture of two or more different compounds Ia with two or more different compounds Ia. However, primarily, a mixture of compounds Ia or Ib refers to a mixture of compounds Ia and compounds Ib, wherein the free radical R in compounds Ia and Ib is 1 Compound Ib in the mixture defined above may be present as a pure E isomer, a pure Z isomer or a mixture of E and Z isomers.

[0055] A similar definition applies to mixtures of compounds III.a, III.b or III.c.

[0056] For the purposes of the present invention, a photosensitizer is an organic molecule (usually a dye) which can convert triplet oxygen into singlet oxygen when subjected to irradiation (usually electromagnetic radiation in the UV, visible or near IR region): after irradiation, the sensitizer forms the corresponding excited singlet state. Intersystem crossing provides an excited triplet state of the sensitizer, thus transferring energy to triplet oxygen to form singlet oxygen.

[0057] "Light" in the correct sense is electromagnetic radiation with a wavelength (range) in the visible spectrum (380nm to 780nm). However, for the purposes of the present invention, unless otherwise specified, the term "light" also encompasses the directly adjacent wavelength spectrum, i.e. near IR (>780nm to 1μm) and near UV (315nm to <380nm).

[0058] Retinol is (2E,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-enyl)non-2,4,6,8-tetraen-1-ol (all trans). For the purposes of the present invention, stereoisomers of retinol relate to retinol, however, wherein one, two, three or all four double bonds in the 2-, 4-, 6- and 8-positions have a Z geometry. Specific examples of such stereoisomers are:

[0059] (2Z,4E,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-enyl)nona-2,4,6,8-tetraen-1-ol;

[0060] (2E,4Z,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-enyl)nona-2,4,6,8-tetraen-1-ol;

[0061] (2Z,4Z,6E,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-enyl)nona-2,4,6,8-tetraen-1-ol;

[0062] or (2Z,4E,6Z,8E)-3,7-dimethyl-9-(2,6,6-trimethylcyclohex-1-enyl)nona-2,4,6,8-tetraen-1-ol (also known as (13Z) retinol according to the carotenoid nomenclature).

[0063] For the purposes of the present invention, retinol derivatives are preferably retinol esters, ie retinol in which the -OH group is esterified to a group -OC(=O)R, wherein R is an organic moiety and is preferably R 2 However, retinol derivatives are also oxidized forms of retinol, such as retinal (-CH2OH group oxidized to -CHO) or retinoic acid (-CH2OH group oxidized to -C(=O)OH).

[0064] Stereoisomers of retinol derivatives are retinol derivatives as defined above, however, wherein one, two, three or all four of the double bonds in the 2-, 4-, 6- and 8-positions have Z geometry.

[0065] Embodiments of the present invention (Ex)

[0066] Typical and preferred embodiments Ex are summarized in the following non-exhaustive list. Other preferred embodiments will become apparent from the paragraphs following this list.

[0067] E.1. A method for preparing a compound of formula Ia or formula Ib or a mixture thereof, or a stereoisomer of said compound Ia or Ib, or a mixture of different stereoisomers of said compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib

[0068]

[0069] in

[0070] R 1 is hydrogen or -C(=O)R 2 ;and

[0071] R 2 It is C1-C 20 -alkyl;

[0072] The method comprises

[0073] (i) providing a reaction mixture comprising a compound of formula II.a, a photosensitizer and optionally a transition metal catalyst:

[0074]

[0075] Where R 1 As defined above;

[0076] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light;

[0077] (iii) contacting the reaction mixture of or obtained in step (ii) with a transition metal catalyst if a transition metal catalyst has not already been provided in step (i);

[0078] (iv.1) if desired, after completion of the reaction, isolating the one or more compounds Ia or Ib obtained in step (ii) or (iii); and

[0079] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0080] or

[0081] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (ii) or (iii); and

[0082] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0083] E.2. The method according to embodiment E.1, wherein R 2 is C1-C4-alkyl or n-C 15 -alkyl.

[0084] E.3. The method according to embodiment E.2, wherein R 2 It is C1-C4-alkyl.

[0085] E.4. The method according to embodiment E.3, wherein R 2 It's methyl.

[0086] E.5. A method according to any one of the preceding embodiments, wherein in the compound II.a R 1 Yes-C(=O)R 2 .

[0087] E.6. The method according to any of the preceding embodiments, wherein the transition metal catalyst comprises a transition metal from Group 4 to Group 12 of the Periodic Table of Elements in elemental or oxidized form.

[0088] E.7. A method according to embodiment E.6, wherein the transition metal catalyst comprises a transition metal from Group 4 to Group 12, Period 4 of the Periodic Table of the Elements in elemental or oxidized form.

[0089] E.8. The method according to any of the preceding embodiments, wherein the transition metal catalyst used in step (i) or (iii) is a heterogeneous catalyst.

[0090] E.9. The method according to embodiment E.7, wherein the heterogeneous transition metal catalyst is a supported catalyst.

[0091] E.10. A method according to embodiment E.8, wherein the heterogeneous transition metal catalyst comprises at least one salt or oxide of a transition metal from Group 4 to Group 12 of the Periodic Table of the Elements supported on a support material.

[0092] E.11. A method according to embodiment E.10, wherein the salt or oxide of the transition metal is a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of a transition metal from Group 4 to Group 12, Period 4 of the Periodic Table of the Elements, or is a chromate, chlorochromate, dichromate or permanganate.

[0093] E.12. A method according to embodiment E.11, wherein the salt or oxide of the transition metal is a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of Cu, Cr, Fe or Ni, or a chromate or dichromate.

[0094] E.13. A method according to embodiment E.12, wherein the chromate or dichromate is an alkali metal, Zn or Fe chromate or dichromate.

[0095] E.14. A method according to any one of embodiments E.12 or E.13, wherein the salt or oxide of the transition metal is selected from the group consisting of: Cu(II) acetate, Cu(ClO4)2, CuCl2, CuO, Co(II) acetate, CrO3 and alkali metal dichromates.

[0096] E.15. The method according to embodiment E.14, wherein the alkali metal dichromate is K2Cr2O7. E.16. The method according to embodiment E.14, wherein the salt or oxide of the transition metal is Cr(VI) oxide (CrO3).

[0097] E.17. A method according to any one of embodiments E.9 to E.16, wherein the support material is selected from the group consisting of: carbon, such as activated carbon; alumina, silica, silicon carbide; aluminosilicates, such as zeolites; titanium dioxide, zirconium dioxide and organic polymers.

[0098] E.18. The method according to embodiment E.17, wherein the support material is an organic polymer.

[0099] E.19. A method according to embodiment E.18, wherein the carrier material is an organic polymer selected from the group consisting of vinylpyridine homopolymers and copolymers, N-vinylpyrrolidine homopolymers and copolymers, styrene homopolymers and copolymers, polyurethanes, acrylate homopolymers and copolymers, and methacrylate homopolymers and copolymers.

[0100] E.20. The method according to embodiment E.19, wherein the organic polymer is selected from the group consisting of 2-vinylpyridine homopolymers and copolymers, 4-vinylpyridine homopolymers and copolymers, and N-vinylpyrrolidine homopolymers and copolymers.

[0101] E.21. A method according to embodiment E.20, wherein the organic polymer is selected from the group consisting of: poly(2-vinylpyridine); poly(4-vinylpyridine); copolymers, preferably block copolymers, of 2-vinylpyridine and methyl methacrylate; and poly(N-vinylpyrrolidine)

[0102] E.22. The method according to embodiment E.21, wherein the organic polymer is selected from the group consisting of polyvinylpyridine, preferably selected from poly(2-vinylpyridine) and poly(4-vinylpyridine).

[0103] E.23. The method of embodiment E.22, wherein the organic polymer is selected from the group consisting of poly(4-vinylpyridine).

[0104] E.24. A method according to any one of the preceding embodiments, wherein the photosensitizer is selected from the group consisting of: fluorescein, eosin, rose bengal, erythrosine, tetraphenylporphyrin, tetraphenylporphyrin cobalt, tetraphenylporphyrin zinc, hematoporphyrin, rhodamine B, Besickel's brilliant red, methyl violet, methylene blue, fullerene C 60 , Fullerene C 70 , graphene, carbon nanotubes, Ru(bpy)3 2+ Salt, Ru(phen)3 2+ Salts, cercosporin, hypocrellin-A and mixtures thereof.

[0105] E.25. A method according to embodiment E.24, wherein the photosensitizer is selected from the group consisting of:

[0106] Tetraphenylporphyrin, Tetraphenylporphyrin Cobalt, Tetraphenylporphyrin Zinc, Methylene Blue, Ru(bpy)3 2+ Salt and Ru(phen)3 2+ Salt.

[0107] E.26. A method according to embodiment E.25, wherein the photosensitizer is selected from the group consisting of:

[0108] Tetraphenylporphyrin, tetraphenylporphyrin zinc and Ru(bpy)3 2+ Salt.

[0109] E.27. A method according to embodiment E.26, wherein the photosensitizer is tetraphenylporphyrin.

[0110] E.28. The method according to any of the preceding embodiments, wherein in step (ii), further photosensitizer is added if this photosensitizer is consumed during irradiation.

[0111] E.29. The method according to any of the preceding embodiments, wherein the photosensitizer is used in a total amount of 0.00001 mol-% to 1 mol-% relative to 1 mol of the compound of formula II.a.

[0112] E.30. The method according to embodiment E.29, wherein the photosensitizer is used in a total amount of 0.0001 mol-% to 0.5 mol-% relative to 1 mol of the compound of formula II.a.

[0113] E.31. The method according to any one of embodiments E.1 to E.28, wherein the photosensitizer is used in a total amount of 0.000005 mol to 0.01 mol per mol of the compound of formula II.a.

[0114] E.32. The method according to embodiment E.31, wherein the photosensitizer is used in a total amount of 0.00001 mol to 0.005 mol per mol of the compound of formula II.a.

[0115] E.33. The method according to embodiment E.32, wherein the photosensitizer is used in a total amount of 0.00001 mol to 0.001 mol per mol of the compound of formula II.a.

[0116] E.34. A method according to any of the preceding embodiments, wherein in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 350 nm to 800 nm.

[0117] E.35. A method according to embodiment E.34, wherein in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 350 nm to 680 nm.

[0118] E.36. A method according to embodiment E.35, wherein in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 400 nm to 650 nm.

[0119] E.37. A method according to embodiment E.36, wherein in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 400 nm to 580 nm.

[0120] E.38. A method according to embodiment E.37, wherein in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 400 nm to 500 nm.

[0121] E.39. A method according to any of the preceding embodiments, wherein in step (ii), the reaction mixture is irradiated with monochromatic light.

[0122] E.40. A method according to embodiment E.39, wherein the irradiation in step (ii) is carried out using a monochromatic light source, preferably an electroluminescent lighting device that emits monochromatic light, wherein at least 90% of the light emitted by the monochromatic light source is within the wavelength range of 350nm to 800nm.

[0123] E.41. A method according to embodiment E.40, wherein at least 90% of the light emitted by the monochromatic light source has a wavelength in the range of 350 nm to 680 nm.

[0124] E.42. A method according to embodiment E.41, wherein at least 90% of the light emitted by the monochromatic light source has a wavelength in the range of 400 nm to 650 nm.

[0125] E.43. A method according to embodiment E.42, wherein at least 90% of the light emitted by the monochromatic light source has a wavelength in the range of 400 nm to 580 nm.

[0126] E.44. A method according to embodiment E.43, wherein at least 90% of the light emitted by the monochromatic light source has a wavelength in the range of 400 nm to 500 nm.

[0127] E.45. A method according to any one of embodiments E.25 to 43, wherein the photosensitizer is tetraphenylporphyrin, tetraphenylporphyrin cobalt or tetraphenylporphyrin zinc, and in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 400 nm to 430 nm, preferably 400 nm to 420 nm, for example 400 nm to 410 nm; or the photosensitizer is methylene blue, and in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 600 nm to 620 nm, or the photosensitizer is Ru(bpy)3 2+ Salt or Ru(phen)3 2+ salt, and in step (ii), irradiating the reaction mixture with light having a wavelength in the range of 450 nm to 480 nm, preferably 460 nm to 475 nm.

[0128] E.46. A method according to any one of embodiments E.39 to E.45, wherein the irradiation in step (ii) is performed using an electroluminescent lighting device that emits monochromatic light, wherein the electroluminescent lighting device consists of at least one LED.

[0129] E.47. A method according to any of the preceding embodiments, wherein the oxygen-containing gas used in step (ii) is selected from the group consisting of: oxygen, air, and a mixture of oxygen and nitrogen, wherein the mixture contains oxygen in a range of 1 wt. % to 99 wt. % relative to the total weight of the mixture.

[0130] E.48. A method according to embodiment E.47, wherein the oxygen-containing gas used in step (ii) is oxygen.

[0131] E.49. The method according to any one of the preceding embodiments, wherein steps (ii) and (iii) are performed neat. E.50. The method according to any one of embodiments E.1 to E.48, wherein steps (ii) and (iii) are performed in the presence of a chlorinated C1-C2-alkane, wherein the molar ratio of the compound (II.a) provided in step (i) to the chlorinated C1-C2-alkane is 50:1 to 1:1.5.

[0132] E.51. The method according to embodiment E.50, wherein the compound (II.a) provided in step (i)

[0133] The molar ratio of the compound (II.a) to the chlorinated C1-C2-alkane is 30:1 to 1:1, preferably 20:1 to 1:1. E.52. The method according to embodiment E.51, wherein the molar ratio of the compound (II.a) provided in step (i) to the chlorinated C1-C2-alkane is 15:1 to 2:1.

[0134] E.53. The method according to any one of embodiments E.50 to E.52, wherein the chlorinated C1-C2-alkane is trichloromethane or tetrachloromethane.

[0135] E.54. A method according to any one of the preceding embodiments, wherein step (ii) is carried out at a temperature of -20°C to 150°C

[0136] E.55. The method according to embodiment E.54, wherein step (ii) is carried out at 0°C to 70°C, preferably 10°C

[0137] to 60°C.

[0138] E.56. A method according to embodiment E.55, wherein step (ii) is carried out at a temperature of 20°C to 50°C.

[0139] E.57. A method according to any of the preceding embodiments, wherein step (ii) is carried out at a pressure of from atmospheric pressure to 100 bar (10 MPa).

[0140] E.58. A method according to embodiment E.57, wherein step (ii) is carried out at a pressure of atmospheric pressure to 10 bar (1 MPa).

[0141] E.59. A method according to any of the preceding embodiments, wherein in step (ii), the entire reaction mixture is irradiated or only different parts of the reaction mixture are irradiated.

[0142] E.60. The method according to any of the preceding embodiments, wherein step (ii) is carried out in a side loop flow photoreactor, a continuous flow photoreactor or a submersible photoreactor.

[0143] E.61. A method according to any of the preceding embodiments, wherein step (ii) is carried out in a reactor comprising a reaction zone for photooxidation and a reaction zone comprising the transition metal catalyst.

[0144] E.62. A method according to any one of the preceding embodiments, comprising:

[0145] (i) providing a reaction mixture comprising a compound of formula II.a, a photosensitizer and a transition metal catalyst;

[0146] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light;

[0147] (iv.1) if desired, after completion of the reaction, isolating the one or more compounds Ia or Ib obtained in step (ii); and

[0148] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0149] or

[0150] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (ii); and

[0151] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0152] E.63. A method according to any one of embodiments E.1 to E.61, comprising:

[0153] (i) providing a reaction mixture comprising a compound of formula II.a and a photosensitizer;

[0154] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light;

[0155] (iii) adding a transition metal catalyst to the reaction mixture obtained in step (ii);

[0156] (iv.1) if desired, after completion of the reaction, isolating the one or more compounds Ia or Ib obtained in step (iii); and

[0157] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0158] or

[0159] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (iii); and

[0160] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0161] E.64. A method according to any one of embodiments E.1 to E.61, comprising:

[0162] (i) providing a reaction mixture comprising a compound of formula II.a and a photosensitizer;

[0163] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light in the first reaction zone;

[0164] (iii) passing the reaction mixture obtained in step (ii) through a second reaction zone comprising a transition metal catalyst;

[0165] and if desired, recycling the reaction mixture obtained in step (iii) to the first reaction zone and the second reaction zone once or several times;

[0166] (iv.1) if desired, after completion of the reaction, isolating the one or more compounds Ia or Ib obtained in step (ii); and

[0167] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0168] or

[0169] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (iii); and

[0170] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0171] E.65. Use of a compound of formula Ia or Ib other than (E)-4-acetoxy-2-methylbut-2-enal, or a stereoisomer of compound Ia or Ib other than (E)-4-acetoxy-2-methylbut-2-enal, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib according to any one of embodiments E.1 to E.5, as an intermediate in the synthesis of retinol, its stereoisomers, its derivatives (preferably its esters) or stereoisomers of its derivatives (preferably stereoisomers of its esters).

[0172] E.66. A hydroperoxide compound of formula III.a, III.b or III.c, or a stereoisomer of said compound of formula III.a, III.b or III.c, or a mixture of different stereoisomers of said compound III.a, III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c

[0173]

[0174] in

[0175] In compound III.a, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl;

[0176] In compound III.b, R 1 Yes-C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl; and

[0177] In compound III.c, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl.

[0178] E.67. A hydroperoxide compound according to embodiment E.66, wherein R 2 It is C1-C4-alkyl.

[0179] E.68. A hydroperoxide compound according to embodiment E.67, wherein R 2 It's methyl.

[0180] E.69. A hydroperoxide compound according to any one of embodiments E.66 to E.68, wherein the hydroperoxide compound is a compound of formula III.a or III.b, or a stereoisomer of the compound of formula III.a or III.b, or a mixture of different stereoisomers of the compound III.a and / or III.b, or a mixture of different compounds III.a and / or III.b.

[0181] E.70. A hydroperoxide compound according to any one of embodiments E.66 to E.68, wherein the hydroperoxide compound is a compound of formula III.a or III.c, or a stereoisomer of the compound of formula III.a or III.c, or a mixture of different stereoisomers of the compound III.a and / or III.c, or a mixture of different compounds III.a and / or IIIc.

[0182] E.71. A hydroperoxide compound according to any one of embodiments E.66 to E.68, wherein the hydroperoxide compound is a compound of formula III.a, or a stereoisomer of the compound of formula III.a, or a mixture of different stereoisomers of the compound III.a, or a mixture of different compounds III.a.

[0183] E.72. Use of a hydroperoxide compound of formula III.a, III.b or III.c, or a stereoisomer of a compound of formula III.a, III.b or III.c, or a mixture of different stereoisomers of compounds III.a, III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c, according to any one of embodiments E.66 to E.71, wherein R 1 It can also be hydrogen, which is used as an intermediate in the synthesis of a compound of formula Ia or Ib according to any one of Embodiments E.1 to E.5, or a stereoisomer of the compound Ia or Ib, or a mixture of different stereoisomers of the compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, or as an intermediate in the synthesis of retinol, its stereoisomers, its derivatives (preferably its esters) or stereoisomers of its derivatives (preferably stereoisomers of its esters).

[0184] E.73. The use according to embodiment E.72, wherein the use is the use of the hydroperoxide compound of formula III.a or III.b, or the stereoisomer of the compound of formula III.a or III.b, or a mixture of different stereoisomers of the compound III.a and / or III.b, or a mixture of different compounds III.a and / or III.b.

[0185] E.74. The use according to embodiment E.72, which is the use of the hydroperoxide compound of formula III.a, or the stereoisomer of the compound of formula III.a, or a mixture of different stereoisomers of the compound III.a, or a mixture of different compounds III.a.

[0186] Without wishing to be bound by theory, it is assumed that in the process according to the invention, the conversion of the compound of the formula II.a into the compound Ia and / or Ib proceeds via a schenkene reaction (= "ene" reaction in which the singlet oxygen is the enophile) and simultaneous (if step (iii) is not carried out) or subsequent (if step (iii) is carried out) transition-metal-catalyzed dehydration (of the hydroperoxide formed in the schenkene reaction via photooxidation).

[0187] In the method of the present invention, if a transition metal catalyst is provided in step (i), the conversion of the compound of formula II.a into compound Ia and / or Ib can be carried out in one step (e.g. as a one-pot reaction). In this case, step (iii) is certainly not carried out. Without wishing to be bound by theory, it is assumed that during step (ii), the compound of formula II.a is converted into allyl hydroperoxide, which is then catalytically dehydrated to obtain compound Ia and / or Ib. It is assumed that compound Ib is the result of double bond isomerization, which can occur during the formation of hydroperoxides and can produce hydroperoxide intermediates III.b as described above or below.

[0188] Alternatively, in the process of the invention, if no transition metal catalyst is provided in step (i), the conversion of the compound of formula II.a into compound Ia and / or Ib can be carried out in two steps. In this case, step (iii) is mandatory. During step (ii), a hydroperoxide is formed, which, after contact with the transition metal catalyst, is dehydrated into compound Ia and / or Ib, as explained above.

[0189] Steps (ii) and (iii) can be repeated several times until the desired conversion is obtained. To achieve this, for example, a reaction mixture containing a compound of formula II.a and a photosensitizer can be circulated in a reactor containing a first reaction zone in which photooxidation occurs and a second reaction zone containing a transition metal catalyst in which dehydration of the hydroperoxide formed in the first reaction zone occurs. Of course, this reaction mode can also be carried out continuously or semi-continuously by continuously or periodically adding II.a and / or photosensitizer to replace the exhausted starting materials and continuously or periodically removing the reaction mixture containing the desired products Ia and / or Ib.

[0190] In a preferred embodiment, the present invention relates to a process for preparing a compound of formula Ia or Ib or a mixture thereof, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib.

[0191]

[0192] in

[0193] R 1 is hydrogen or -C(=O)R 2 ;and

[0194] R 2 It is C1-C 20 -alkyl;

[0195] The method comprises

[0196] (i) providing a reaction mixture comprising a compound of formula II.a, a photosensitizer and a transition metal catalyst:

[0197]

[0198] Where R 1 As defined above;

[0199] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light;

[0200] (iv.1) if desired, after the reaction is complete (to the desired extent), isolating the one or more compounds (Ia) or (Ib) obtained in step (ii); and

[0201] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0202] or

[0203] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (ii); and

[0204] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0205] In another preferred embodiment, the present invention relates to a process for preparing a compound of formula Ia or Ib or a mixture thereof, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib.

[0206]

[0207] in

[0208] R 1 is hydrogen or -C(=O)R 2 ;and

[0209] R 2 It is C1-C 20 -alkyl;

[0210] The method comprises

[0211] (i) providing a reaction mixture comprising a compound of formula II.a and a photosensitizer:

[0212]

[0213] Where R 1 As defined above;

[0214] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light;

[0215] (iii) adding a transition metal catalyst to the reaction mixture obtained in step (ii);

[0216] (iv.1) if desired, after completion of the reaction (to the desired extent), isolating the one or more compounds (Ia) or (Ib) obtained in step (iii); and

[0217] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0218] or

[0219] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (iii); and

[0220] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0221] In yet another preferred embodiment, the present invention relates to a process for preparing a compound of formula Ia or Ib or a mixture thereof, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib.

[0222]

[0223] in

[0224] R 1 is hydrogen or -C(=O)R 2 ;and

[0225] R 2 It is C1-C 20 -alkyl;

[0226] The method comprises

[0227] (i) providing a reaction mixture comprising a compound of formula II.a and a photosensitizer:

[0228]

[0229] Where R 1 As defined above;

[0230] (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light in the first reaction zone;

[0231] (iii) passing the reaction mixture obtained in step (ii) through a second reaction zone comprising a transition metal catalyst;

[0232] and if desired, recycling the reaction mixture obtained in step (iii) to the first reaction zone and subsequently to the second reaction zone once or several times;

[0233] (iv.1) if desired, after the reaction is complete (to the desired extent), isolating the one or more compounds (Ia) or (Ib) obtained in step (ii); and

[0234] (v.1) if desired, hydrolyzing the one or more compounds Ia or Ib isolated in step (iv.1) to form compounds Ia or Ib wherein R 1 It is hydrogen;

[0235] or

[0236] (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (iii); and

[0237] (v.2) if desired, isolating the one or more compounds Ia or Ib obtained in step (iv.2).

[0238] In compounds Ia, Ib and II.a, R 2 Preferably it is C1-C4-alkyl or n-C 15 -alkyl, more preferably C1-C4-alkyl, even more preferably C1-C2-alkyl and in particular methyl.

[0239] R 1 Preferably -C(=O)R 2 , especially in compound II.a.

[0240] The transition metal catalyst used in step (i) or (iii) may be a homogeneous or heterogeneous catalyst. In a homogeneous catalyst, the catalyst is in the same phase as the reactants or products, whereas in a heterogeneous catalyst, the catalyst is in a different phase from the reactants or products. Thus, for the purposes of the present invention, a heterogeneous catalyst is a catalyst that is insoluble in the reaction medium.

[0241] The transition metal catalyst used in step (i) or (iii) is preferably a heterogeneous catalyst.

[0242] Heterogeneous catalysts are generally full catalysts or supported catalysts. Full catalysts are catalysts in which the active metal in its elemental or oxidized form constitutes the major part of the catalyst in its active form, i.e. more than 50% by weight, in particular at least 80% by weight. Supported catalysts are catalysts in which the active metal is supported on a support material.

[0243] Preferably, the heterogeneous transition metal catalyst is a supported catalyst.

[0244] In metal salts, the catalytically active metal may be part of the cation or part of the anion.

[0245] In this context, metal compounds are, for example, metal oxides (which are generally not fractionated in metal salts) and metal complexes (coordination compounds).

[0246] The active metal of the metal catalyst is a transition metal. "Active" metal means that this metal is a catalytic active site. If the active metal is part of the anion (such as in permanganate, chromate, dichromate, etc.), it is not necessarily a transition metal, and the transition metal catalyst may contain other metals, for example, to achieve charge balance.

[0247] Preferably, the transition metal catalyst comprises a transition metal from Group 4 to Group 12 of the Periodic Table of Elements in elemental or oxidized form. More preferably, the transition metal catalyst comprises a transition metal from Group 4 to Group 12 of the Periodic Table of Elements in oxidized form.

[0248] The group numbering is related to the IUPAC nomenclature of 1985. Thus, groups 4 to 12 are the Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn groups.

[0249] Preferably, the transition metal catalyst comprises a transition metal from Group 4 to Group 12, Period 4 of the Periodic Table of Elements (i.e., Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) in elemental or oxidized form. More preferably, the transition metal catalyst comprises a transition metal from Group 4 to Group 12, Period 4 of the Periodic Table of Elements (i.e., Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) in oxidized form.

[0250] Preferably, the transition metal catalyst comprises a transition metal salt or a transition metal oxide, more preferably a salt or oxide of a metal of Group 4 to Group 12 of the Periodic Table and even more preferably a salt or oxide of a metal of Group 4 to Group 12, Period 4 of the Periodic Table.

[0251] The metal salt or oxide is preferably a transition metal C2-C8-carboxylate (RC(=O)O - , wherein R is C1-C7-alkyl, such as acetate, propionate, butyrate, etc.), a halide (such as fluoride, chloride, bromide, iodide), nitrate, phosphate, sulfate, chlorate, perchlorate or oxide, more preferably a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of a transition metal from Group 4 to Group 12 of the Periodic Table of the Elements, even more preferably a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of a transition metal from Group 4 to Group 12 of the Periodic Table of the Elements; or a chromate, chlorochromate, dichromate or permanganate.

[0252] More preferably, the salt or oxide of the transition metal is a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of Cu, Cr, Fe or Ni, or is a chromate or dichromate, which chromate or dichromate is preferably an alkali metal, Zn or Fe chromate or dichromate.

[0253] Even more preferably, the salt or oxide of the transition metal is selected from the group consisting of Cu(II) acetate, Cu(ClO4)2, CuCl2, CuO, Co(II) acetate, CrO3 and alkali metal dichromates, the latter preferably being K2Cr2O7.

[0254] In particular, the transition metal catalyst includes Cr(VI) oxide (CrO3).

[0255] As stated, the transition metal catalyst is preferably a supported catalyst.

[0256] Suitable support materials are known in the art and are, for example, carbon, such as activated carbon; alumina, silica, silicon carbide; aluminosilicates, such as zeolites; titanium dioxide, zirconium dioxide or organic polymers.

[0257] Suitable organic polymers are, for example, vinylpyridine homopolymers and copolymers, N-vinylpyrrolidine homopolymers and copolymers, styrene homopolymers and copolymers, polyurethanes, acrylate homopolymers and copolymers and methacrylate homopolymers and copolymers.

[0258] Preferably, the carrier material is an organic polymer. The organic polymer is preferably selected from the group consisting of vinylpyridine homopolymers and copolymers, N-vinylpyrrolidine homopolymers and copolymers, styrene homopolymers and copolymers, polyurethanes, acrylate homopolymers and copolymers and methacrylate homopolymers and copolymers, more preferably from 2-vinylpyridine homopolymers and copolymers, 4-vinylpyridine homopolymers and copolymers and N-vinylpyrrolidine homopolymers and copolymers, even more preferably from poly(2-vinylpyridine); poly(4-vinylpyridine); copolymers, preferably block copolymers, of 2-vinylpyridine and methyl methacrylate; and poly(N-vinylpyrrolidine), and in particular from polyvinylpyridine, in particular poly(2-vinylpyridine) or poly(4-vinylpyridine), very in particular poly(4-vinylpyridine).

[0259] The molecular weight of the polymer can vary over a wide range. For example, the polymer can have a number average molecular weight (M) of 500 to 1,000,000, such as 2,000 to 500,000 or 10,000 to 300,000. n ) and a weight average molecular weight (M) of 700 to 2,000,000, for example, 5000 to 1,000,000 or 15,000 to 500,000. w ).

[0260] The polymers may also be cross-linked to enhance stability and / or load-bearing capacity.

[0261] Typical crosslinking materials for polyvinylpyridine are, for example, divinylbenzene. The degree of crosslinking depends on the desired stiffness of the material and may be in the range of 1% to 40%, preferably 2% to 30%, more preferably 10% to 30%, in particular 20% to 30%. The degree of crosslinking is the quotient of the number of moles of crosslinking agent and the total number of moles of building blocks present in the crosslinked macromolecular network, expressed here in % (e.g., polyvinylpyridine crosslinked with 1% divinylbenzene means 99 mol of vinylpyridine crosslinked with 1 mol of divinylbenzene). The degree of crosslinking is usually determined by analysis, for example by rheology.

[0262] Depending on the properties of the metal substance and the support material of the catalyst, the bonding between the catalytic metal substance and the support material can be carried out, for example, by adsorption, electrostatic interaction, coordination bonding or covalent bonding. As an example only, if the nitrogen atom of the pyridine ring is quaternized, for example, by protonation or alkylation, the polyvinyl pyridine support material preferably used can interact electrostatically with a negatively charged metal substance (that is, if the metal is part of an anion, such as in permanganate, chromate or dichromate). If the metal substance in the metal oxide or metal salt in which the metal is part of a cation or a complex cation or in which the metal is part of an anion and a balancing cation is a metal substance that can coordinate with the nitrogen atom of pyridine (such as in Ag, Fe or Zn chromate or dichromate), the polyvinyl pyridine support material usually interacts in a coordination manner, and the nitrogen atom of the pyridine ring serves as a ligand.

[0263] The catalyst loading of active metal (i.e. transition metal, e.g. Group 4 to Group 12 transition metal), i.e. the amount of active metal in the supported catalyst, is preferably in the range of 1% to 20% by weight, more preferably 1% to 15% by weight, even more preferably 1% to 10% by weight, in particular 2% to 10% by weight, relative to the total (dry) weight of the supported catalyst. The percentage is related only to the active metal and not to any salt or oxide or other form of the metal actually present therein (e.g., in the case where Cr is present in the form of CrO3 or chromate or dichromate, etc., the percentage is related only to Cr). The loading can be determined analytically, e.g. by atomic absorption spectroscopy, or can be calculated according to the preparation method.

[0264] Alternatively, the catalyst loading of the active metal salt or oxide or complex (i.e. a transition metal, e.g. a salt or oxide or complex of a transition metal from Group 4 to Group 12), i.e. the amount of the form in which the active metal is present in the supported catalyst, is preferably in the range of 2% to 40% by weight, more preferably 3% to 35% by weight, even more preferably 5% to 30% by weight, in particular 5% to 20% by weight, relative to the total (dry) weight of the supported catalyst. The percentage is related to the weight of the form in which the active metal is present, i.e. to the salt or oxide or other form of the metal actually present (e.g. in the case where Cr is present in the form of CrO3 or chromate or dichromate etc., the percentage is related to CrO3 or chromate or dichromate). The loading can be determined analytically, e.g. by atomic absorption spectroscopy, or can be calculated according to the preparation method.

[0265] Supported transition metal catalysts suitable for use in the process according to the present invention are commercially available or can be obtained by methods known in the art, for example, by bringing a metal substance or a precursor thereof and a support material or a precursor thereof into close contact with each other, if necessary in the presence of a solvent that can be removed later; if necessary or convenient, under heating. If necessary, the precursor of the metal substance or the support material is first treated to convert it into a form that can interact with the partner. By way of example only, if the support material is polyvinylpyridine to be electrostatically interacted with a negatively charged metal substance, the polyvinylpyridine is first quaternized, for example, by contacting the polyvinylpyridine with a Bronsted acid to protonate (a portion of) the nitrogen atom of the pyridine ring or with an alkylating agent (e.g., an alkyl bromide or iodide or a sulfate, such as butyl bromide) to alkylate (a portion of) the nitrogen atom of the pyridine ring, and then the resulting support material having the quaternized nitrogen atom of the pyridine ring is contacted with a salt of a negatively charged metal substance to exchange anions, thereby binding the metal substance to the support material via ionic interactions.

[0266] The catalyst (calculated based on the active metal content) is preferably used in an amount of 0.0001 mol-% to 15 mol-%, more preferably 0.001 mol-% to 10 mol-%, even more preferably 0.01 mol-% to 5 mol-%, particularly 0.1 mol-% to 5 mol-%, specifically 1 mol-% to 5 mol-%, more specifically 1 mol-% to 3 mol-%, relative to 1 mol of compound II.a.

[0267] Support materials are commercially available (eg, from Acros Chemicals, Merck, or Vertellus).Polymeric support materials are often commercialized as ion exchange resins.

[0268] The heterogeneous catalyst can be used in bulk, loose form, or can be immobilized, for example in a fixed bed.

[0269] As explained above, the photosensitizer used in the method of the invention is a compound that can convert triplet oxygen into singlet oxygen when subjected to irradiation (usually electromagnetic radiation in the UV, visible or near IR region): after irradiation, the sensitizer forms the corresponding excited singlet state. Intersystem crossing provides the excited triplet state of the sensitizer, thus transferring energy to triplet oxygen to form singlet oxygen. Singlet oxygen is the substance that oxidizes compound II.a to the corresponding hydroperoxide (or its double bond isomer).

[0270] Preferably, the photosensitizer can convert triplet oxygen into singlet oxygen when subjected to electromagnetic radiation in the near UV, visible or near IR region, more preferably in the visible or near IR region, especially in the visible region.

[0271] Preferably, the photosensitizer is selected from the group consisting of: fluorescein, eosin, rose bengal (RB), erythrosine, tetraphenylporphyrin (more specifically, 5,10,15,20-tetraphenyl-21H,23H-porphyrin; TPP; 2HTPP), cobalt tetraphenylporphyrin (Co-TPP; i.e., a cobalt complex of TPP and Co(II)), zinc tetraphenylporphyrin (Zn-TPP; i.e., a zinc complex of TPP and Zn(II)), hematoporphyrin, rhodamine B, Besickel's brilliant red, methyl violet, methylene blue, fullerene C 60 , Fullerene C 70 , graphene, carbon nanotubes, Ru(bpy)3 2+ salts (bpy = 2,2'-bipyridine) (e.g. tris(2,2'-bipyridine)ruthenium(II) hexafluorophosphate, tris(2,2'-bipyridine)ruthenium(II) chloride, usually in the form of hexahydrate), Ru(phen)3 2+ salt (phen = 1,10-phenanthroline) (e.g. dichlorotri(1,10-phenanthroline) ruthenium (II) chloride), cercosporin, hypocrellin-A and mixtures thereof. More preferably, the photosensitizer is selected from the group consisting of tetraphenylporphyrin, cobalt tetraphenylporphyrin, zinc tetraphenylporphyrin, methylene blue, Ru(bpy)3 2+ A salt (particularly tris(2,2'-bipyridyl)ruthenium(II) hexafluorophosphate, tris(2,2'-bipyridyl)ruthenium(II) chloride or its hexahydrate) and Ru(phen)3 2+ A salt (particularly dichlorotris(1,10-phenanthroline)ruthenium(II) chloride), particularly selected from the group consisting of tetraphenylporphyrin, zinc tetraphenylporphyrin and Ru(bpy)3 2+ salt (particularly tris(2,2'-bipyridyl)ruthenium(II) hexafluorophosphate, tris(2,2'-bipyridyl)ruthenium(II) chloride or a hexahydrate thereof); and specifically tetraphenylporphyrin.

[0272] The photosensitizer can be provided in step (i) in very small amounts. However, during the irradiation, part of the photosensitizer may degrade, resulting in less and less singlet oxygen generation and thus slowing down the conversion of compound II.a into the corresponding hydroperoxide and ultimately into the desired compound Ia and / or Ib. Therefore, a larger amount of photosensitizer is provided in step (i), or, during step (ii), if this photosensitizer is depleted during the irradiation, further photosensitizer is added. The degree of depletion / degradation of the photosensitizer can be monitored during step (ii), for example by UV / Vis spectroscopy, which can also be performed in coordination.

[0273] The photosensitizer is preferably used in a total amount of 0.00001 mol-% to 1 mol-% relative to 1 mol of the compound of formula II.a. The total amount means the total amount of the photosensitizer provided in step (i) and added during step (ii) (if applicable). More preferably, the photosensitizer is used in a total amount of 0.0001 mol-% to 0.5 mol-%, even more preferably 0.0001 mol-% to 0.2 mol-%, for example 0.0005 mol-% to 0.2 mol-% or 0.001 mol-% to 0.1 mol-%, relative to 1 mol of the compound of formula II.a.

[0274] Alternatively, the photosensitizer is preferably used in a total amount of 0.0000001 mol to 0.01 mol, more preferably 0.000001 mol to 0.01 mol or 0.000001 mol to 0.005 mol, even more preferably 0.000001 mol to 0.002 mol or 0.000005 mol to 0.01 mol, particularly preferably 0.00001 mol to 0.001 mol, specifically 0.00001 mol to 0.005 mol or 0.00001 mol to 0.001 mol, for example 0.00001 mol to 0.0005 mol, per 1 mol of the compound of formula II.a.

[0275] Typical photosensitizers are dyes and can therefore be excited by electromagnetic radiation in the near UV, visible or near infrared (near IR; NIR) electromagnetic spectrum. Thus, preferably in step (ii), the reaction mixture is irradiated with light in the near UV, visible or near IR range. More preferably, in step (ii), the reaction mixture is irradiated with light in the visible or near IR range and in particular in the visible range.

[0276] Preferably, in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 350 nm to 800 nm, more preferably 350 nm to 680 nm, even more preferably in the range of 400 nm to 650 nm, even more preferably 400 nm to 580 nm and in particular 400 nm to 500 nm. The optimal wavelength range generally depends on the photosensitizer used and, if it is not known anyway to the person skilled in the art, can be determined, for example, by short-term tests, or can be selected by UV spectroscopy.

[0277] For example, if the photosensitizer is tetraphenylporphyrin, tetraphenylporphyrin cobalt or tetraphenylporphyrin zinc, in step (ii), the reaction mixture may be irradiated, for example, with light having a wavelength in the range of 400 nm to 430 nm, preferably 400 nm to 420 nm, for example 400 nm to 410 nm; if the photosensitizer is methylene blue, in step (ii), the reaction mixture may be irradiated, for example, with light having a wavelength in the range of 600 nm to 620 nm, or if the photosensitizer is Ru(bpy)3 2+ Salt or Ru(phen)3 2+ If a salt is present, then in step (ii), the reaction mixture may be irradiated, for example, with light having a wavelength in the range of 450 nm to 480 nm, preferably 460 nm to 475 nm.

[0278] In step (ii), the reaction mixture is preferably irradiated with monochromatic light.

[0279] In theory, monochromatic light is light with a single constant frequency / light with a single vacuum wavelength range. However, in practice, there is no radiation that can be completely monochromatic. Therefore, in practice, "monochromatic" light - even from a laser or a spectral line - always consists of components with a certain non-zero width frequency range. For the purposes of the present invention, monochromatic light is understood to be light produced by a monochromatic light source of the prior art, such as a monochromator, a filter, an Hg vapor lamp (high-pressure, medium-pressure or low-pressure lamp) (usually in combination with a filter), a doped Hg vapor lamp (if necessary, in combination with a filter), a Na vapor lamp (high-pressure or low-pressure lamp), a laser or in particular a monochromatic LED.

[0280] Preferably, the irradiation in step (ii) is carried out using a monochromatic light source, preferably an electroluminescent lighting device emitting monochromatic light, wherein at least 90% of the light emitted by the monochromatic light source is within the wavelength range of 350nm to 800nm, preferably 350nm to 680nm, more preferably 400nm to 650nm, even more preferably 400nm to 580nm, in particular 400nm to 500nm.

[0281] Preferably, the irradiation in step (ii) is performed using an electroluminescent lighting device emitting monochromatic light, wherein the electroluminescent lighting device consists of at least one LED.

[0282] The oxygen-containing gas used in step (ii) is preferably selected from the group consisting of oxygen, air and a mixture of oxygen and nitrogen, the mixture containing, relative to the gross weight of the mixture, a range of 1 wt % to 99 wt % oxygen. More preferably, the oxygen-containing gas used in step (ii) is selected from the group consisting of oxygen, air and a mixture of oxygen and nitrogen, the mixture containing a range of 20 wt % to 99 wt % oxygen, and in particular oxygen.

[0283] "Passing an oxygen-containing gas through the reaction mixture provided in step (i)" is not limited to bubbling an oxygen-containing gas through the mixture, thereby allowing most of the oxygen-containing gas to escape, but also encompasses inserting and maintaining the oxygen-containing gas in the reaction mixture, for example by using a closed, usually pressurized reaction vessel.

[0284] Preferably, steps (ii) and (iii) are carried out purely (i.e. substantially). "Purely" or "substantially" means that there is no additional solvent. The "additional" in this specification takes into account the fact that the starting compound II.a and the hydroperoxide formed in the middle can serve as a solvent or dispersant for the photosensitizer and the transition metal catalyst. In order to carry out step (ii) purely, the reaction mixture provided in step (i) is prepared, for example, by mixing the starting materials (if the reaction is to be carried out in one step, it is compound II.a, photosensitizer, transition metal catalyst) in the absence of any additional solvent, or by mixing the starting materials in the presence of an additional solvent, and then removing it before carrying out step (ii).

[0285] In an alternatively preferred embodiment, steps (ii) and (iii) are carried out in the presence of a chlorinated C1-C2-alkane. For this purpose, the chlorinated C1-C2-alkane is conveniently provided in the reaction mixture of step (i). The molar ratio of compound (II.a) provided in step (i) to the chlorinated C1-C2-alkane is 50:1 to 1:1.5, more preferably 30:1 to 1:1, even more preferably 20:1 to 1:1, in particular 15:1 to 2:1. The chlorinated C1-C2-alkane is preferably trichloromethane or tetrachloromethane.

[0286] However, it is more preferred that steps (ii) and (iii) are performed neat.

[0287] Step (ii) is preferably carried out at a temperature of -20 to 150°C, more preferably 0 to 70°C, for example 0 to 60°C, or 5 to 50°C, or 20 to 50°C.

[0288] Step (ii) is preferably carried out at a pressure of atmospheric pressure to 100 bar (10 MPa). Atmospheric pressure means the local ambient pressure and is therefore approximately 1013.25 hPa ± 200 hPa. In a more preferred embodiment, step (ii) is carried out at a pressure of atmospheric pressure to 10 bar (> 0.1 mPa to 1 mPa).

[0289] In step (ii) the entire reaction mixture may be irradiated or only different parts of the reaction mixture may be irradiated. For example, the latter may occur if only a portion of the reaction mixture (e.g. only 20% to 90% by weight, or 30% to 80% by weight, or 50% to 80% by weight of the reaction mixture) is passed through the irradiation source.

[0290] In a specific embodiment, step (ii) is carried out so that a portion of the starting compound II.a remains unreacted. This ensures that compound II.a can still serve as a solvent for other substances present in the reaction mixture. Preferably, at least 20%, more preferably at least 50% of the initial charge of compound II.a remains unreacted in step (ii). After post-treatment, separation and purification (as desired), compound II.a can be reused in step (i). The degree of conversion of compound II.a can be determined by conventional means, such as periodic or continuous sample collection and analysis or coordinated analysis of the composition of the reaction mixture, or by passing oxygen through the reaction mixture in a predetermined substoichiometric amount. The reaction in step (ii) is interrupted, for example, by stopping the oxygen feed and / or by stopping the irradiation.

[0291] Steps (ii) and (iii) can be carried out in any reactor known in the art to be suitable for photooxidation. Suitable reactors contain at least means for introducing an oxygen-containing gas and a radiation source. In addition, the reactor conveniently contains an agitator and means for cooling or heating.

[0292] Examples of suitable reactors are side loop flow photoreactors, continuous flow photoreactors or submersible photoreactors.

[0293] In order to circulate the reaction mixture containing the compound of formula II.a and the photosensitizer in a reactor containing a first reaction zone in which photooxidation occurs and a second reaction zone containing a transition metal catalyst in which dehydration of the hydroperoxide formed in the first reaction zone occurs, a suitable reactor preferably contains a pump and a pipeline to circulate the reaction mixture, i.e., from one zone to another. For example, a photoreactor is connected to a reactor containing a transition metal catalyst so that the reaction mixture can circulate between the photoreactor and the reactor containing the metal transition catalyst.

[0294] After the reaction is complete, step (ii) (if step (iii) is not carried out) or the reaction mixture obtained in step (iii) is usually treated. In this context, "completion" of the reaction does not necessarily mean the maximum conversion of the starting material, but rather the conversion to the desired degree. As explained above, the starting compound II.a usually serves as a solvent, especially if step (ii) is carried out neat. In this case, the reaction is conveniently stopped significantly before the maximum conversion of II.a.

[0295] Step (ii) (if step (iii) is not carried out) or the workup of the reaction mixture obtained in step (iii) can be carried out by conventional means, such as separation from the transition metal catalyst (if necessary) and by separation from other components of the reaction mixture such as unreacted compound II.a, photosensitizer or undesirable by-products and (if desired) from each other to separate the desired reaction products Ia and / or Ib (step (iv.1)). The separation can be carried out by conventional means, such as extraction, distillation or chromatography.

[0296] If compounds Ia or Ib are formed as different stereoisomers, these can be separated from one another if desired.

[0297] In order to obtain compounds Ia and / or Ib, wherein R 1 is hydrogen, the compound Ia and / or Ib isolated according to step (iv.1) or from step (ii) (if step (iii) is not carried out) or the reaction mixture obtained from step (iii) is hydrolyzed, for example by reaction with an acid or with a base. If in compound II.a (and therefore also in the obtained compound Ia and / or Ib) R 1 Yes-C(O)R 2 , then hydrolysis is of course necessary (to obtain compounds Ia and / or Ib, wherein R 1 is hydrogen), but if in compound II.a R 1 It may also be necessary if the acylating agent is hydrogen, since a portion of the hydroxyl groups may be acylated by the acylating agent, especially if the acylating agent is used in excess.

[0298] If the reaction mixture obtained from step (ii) (if step (iii) is not carried out) or from step (iii) is hydrolyzed (step (v.1)), the reaction mixture obtained can be worked up and the desired reaction products Ia and / or Ib (step (iv.1)) can be separated from the other components of the reaction mixture and also from each other by customary means, such as extraction, distillation or chromatography.

[0299] The method of the present invention provides a simple method for preparing compounds Ia and / or Ib starting from readily available bulk chemicals prenyl alcohol and prenyl alcohol ester II.a. Compounds Ia and Ib can serve as retinol, its stereoisomers, derivatives thereof (preferably esters thereof; in particular, wherein the OH group of retinol is esterified to -OC(O)R 2 esters of retinol) or stereoisomers of their derivatives (preferably stereoisomers of their esters; in particular, wherein the OH group of retinol is esterified to -OC(O)R 2 Compound Ia can be converted into compound Ib by known Pd-catalyzed double bond isomerization reactions, as described, for example, in US 4,124,619 or CN 103467287.

[0300] Furthermore, the present invention relates to the use of a compound of formula Ia or Ib other than (E)-4-acetoxy-2-methylbut-2-enal, or a stereoisomer of compound Ia or Ib other than (E)-4-acetoxy-2-methylbut-2-enal, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib as defined above, as retinol, its stereoisomers, its derivatives (preferably its esters; in particular wherein the OH group of retinol is esterified to -OC(O)R 2 esters of) or stereoisomers of their derivatives (preferably stereoisomers of their esters; in particular, wherein the OH group of retinol is esterified to -OC(O)R 2 As explained above, compound Ia can be easily converted to Ib. The latter can be reacted with β-ionideneethyltriphenylphosphonium salt to retinol in a Wittig reaction (if R in Ib is 1 =H, this directly produces), its stereoisomers, its esters (if in Ib R 1 =-C(O)R 2 , where the OH group of retinol is esterified to -OC(O)R 2 The ester is directly produced) or a stereoisomer of its ester, as described, for example, by J. Paust et al. in Carotenoids, 1996, Vol. 2, pp. 258-292, in US 5,087,762, or in H. Ernst, Pure Appl. Chem. 2002, 74, 2213 or in GL Parker et al., Tetrahedron 2016, 72, 1645-1652. Other retinol derivatives are obtainable by conventional means; for example, by using different R 2Retinol (or its stereoisomer) is esterified by esterification of retinol (or its stereoisomer) with an acid or acid derivative of -C(O)OH or its derivative; or by oxidation of retinol (or its stereoisomer) to retinal (or its stereoisomer) or retinoic acid (or its stereoisomer). Retinol (or its stereoisomer) is obtained by saponification (ester cleavage) of a retinol ester (or its stereoisomer). These transformations are well known in the art.

[0301] Furthermore, the present invention relates to a hydroperoxide compound of the formula III.a, III.b or III.c, or a stereoisomer of a compound of the formula III.a, III.b or III.c, or a mixture of different stereoisomers of the compound III.a and / or III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c

[0302]

[0303] in

[0304] In compound III.a, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl;

[0305] In compound III.b, R 1 Yes-C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl; and

[0306] In compound III.c, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl.

[0307] The hydroperoxides III.a, III.b and III.c are formed in step (ii) of the process according to the invention. If the reaction mixture provided in step (i) does not contain an acylating agent, the hydroperoxides formed in step (ii) can be detected and also isolated, since their further reaction / decomposition in the absence of an acylating agent is rather slow.

[0308] The present invention preferably relates to a hydroperoxide compound of the formula III.a or III.b, or a stereoisomer of a compound of the formula III.a or III.b, or a mixture of different stereoisomers of compounds III.a and / or III.b, or a mixture of different compounds III.a and / or III.b.

[0309] The present invention alternatively preferably relates to one hydroperoxide compound of formula III.a or III.c, or a stereoisomer of a compound of formula III.a or III.c, or a mixture of different stereoisomers of compounds III.a and / or III.c, or a mixture of different compounds III.a and / or III.c.

[0310] The present invention particularly relates to a hydroperoxide compound of the formula III.a, or a stereoisomer of a compound of the formula III.a, or a mixture of different stereoisomers of a compound III.a, or a mixture of different compounds III.a.

[0311] Furthermore, the present invention relates to the use of a hydroperoxide compound of the formula III.a, III.b or III.c as defined above, or a stereoisomer of a compound of the formula III.a, III.b or III.c, or a mixture of different stereoisomers of compounds III.a, III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c, wherein, however, in compound III.b R 1 It may also be hydrogen, which is used as an intermediate in the synthesis of a compound of formula Ia or Ib as defined above, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, or as retinol, its stereoisomers, its derivatives (preferably its esters; in particular wherein the OH group of retinol is esterified to -OC(O)R 2 esters of) or stereoisomers of their derivatives (preferably stereoisomers of their esters; in particular, wherein the OH group of retinol is esterified to -OC(O)R 2 esters) in the synthesis of intermediates.

[0312] The conversion of compound III.a and / or III.b into compound Ia and / or Ib is carried out by subjecting compound III.a and / or III.b to step (iii) and optionally steps (iv) and (v) of the method of the present invention described above. Compound Ia and / or Ib can be converted into retinol, its stereoisomers, its derivatives or stereoisomers of its derivatives as described above.

[0313] The present invention preferably relates to the use of a hydroperoxide compound of formula III.a or III.b as defined above, or a stereoisomer of a compound of formula III.a or III.b, or a mixture of different stereoisomers of compounds III.a and / or III.b, or a mixture of different compounds III.a and / or III.b, wherein, however, in compound III.b R1 It may also be hydrogen, which is used as an intermediate in the synthesis of a compound of formula Ia or Ib as defined above, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, or as retinol, its stereoisomers, its derivatives (preferably its esters; in particular wherein the OH group of retinol is esterified to -OC(O)R 2 esters of) or stereoisomers of their derivatives (preferably stereoisomers of their esters; in particular, wherein the OH group of retinol is esterified to -OC(O)R 2 esters) in the synthesis of intermediates.

[0314] The present invention particularly relates to the use of a hydroperoxide compound of formula III.a, or a stereoisomer of a compound of formula III.a, or a mixture of different stereoisomers of compound III.a, or a mixture of different compounds III.a, as an intermediate in the synthesis of a compound of formula Ia or Ib, or a stereoisomer of compound Ia or Ib, or a mixture of different stereoisomers of compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib as defined above, or as retinol, its stereoisomers, its derivatives (preferably its esters; in particular wherein the OH group of retinol is esterified to -OC(O)R 2 esters of) or stereoisomers of their derivatives (preferably stereoisomers of their esters; in particular, wherein the OH group of retinol is esterified to -OC(O)R 2 esters) in the synthesis of intermediates.

[0315] The following examples are used to further illustrate the present invention.

[0316] Example

[0317] Compounds by 1 H-NMR and also partially through 13 The signals are characterized by C-NMR. NMR analysis was performed on Bruker 400 MHz and 500 MHz spectrometers in CDCl3. The signals are characterized by the chemical shift (ppm) relative to tetramethylsilane, their multiplicity and their integration (relative number of given hydrogen atoms). The following abbreviations are used to characterize the multiplicity of the signals: m = multiplet, q = quartet, t = triplet, d = doublet and s = singlet.

[0318] A. Preparation of Metal Catalyst CrO3-PVPy (CrO3 on Poly-(4-vinylpyridine))

[0319] equipment:

[0320] Four-necked reaction flask, stirrer, thermometer, dropping funnel, nitrogen seal.

[0321] General procedure:

[0322] In a 1 L reaction flask, 200 g of 25% poly-(4-vinylpyridine crosslinked with divinylbenzene from Acros Chemicals (sieved to a grain size of 0.85 mm-1.0 mm) were placed in 400 mL of water under a nitrogen atmosphere. A solution of 20.0 g (0.2 mmol) of chromium (VI) oxide and 60 mL of water was added dropwise at room temperature with slight cooling. The orange reaction mixture was stirred at 150 rpm overnight at room temperature and then filtered through a glass suction filter. The spherical residue was washed twice with 500 mL of water each time and then dried in a vacuum drying oven at 50° C. and 30 mbar for at least 12 hours. The chromium content was analyzed by atomic absorption spectroscopy. The CrO3-PVPy catalyst with higher or lower amounts of CrO3 can be adapted accordingly by using The amount of CrO3 and / or polymer is obtained .

[0323] B. Photooxidation

[0324] 1. Photooxidation of isoprene acetate in a G1-Corning photoreactor and using CrO3-PVPy Rearrangement / Dehydration

[0325] Example 1 to Example 3

[0326] equipment:

[0327] G1-Corning photoreactor (5 tempered G1 plates, layer thickness approximately 1 mm, each illuminated on both sides by LEDs, a total of 200 LEDs with a wavelength of 405 nm and a total radiant power of 195 W);

[0328] A 100 mL mini-unit reactor with an impeller stirrer as a feed vessel;

[0329] 8 bar relief valve;

[0330] A glass column (d = 2.5 cm) filled with CrO3-PVPy;

[0331] Two FLOM two-stroke piston pumps in parallel, each with a maximum speed of 99.9mL / min

[0332] experiment:

[0333] 266.4 g (2078.6 mmol, 1 eq.) of isoprene acetate (IPA) were placed in a glass vial, 11.71 g (60.3 mmol, 0.029 eq.) of dimethyl phthalate were added as an NMR internal standard, and 43.2 mg (70.27 μmol, 0.000034 eq.) of photosensitizer tetraphenylporphyrin (TPP) were dissolved in the mixture. The reaction mixture was transferred to a Corning photoreactor via a 100 mL mini-device reactor, stirred at 100 rpm and circulated in the system by pumping the solution downstream of the Corning photoreactor through a safety valve that was opened only at 8 bar to increase the oxygen solubility. Downstream of the valve, the reaction mixture was passed without pressure through a glass column containing 38 g of CrO3-PVPy (approximately 15 wt.% CrO3 loaded relative to the total weight of the supported catalyst), where the hydroperoxides formed in the Corning photoreactor were converted into compounds Ia and Ib, where R 1 =C(O)CH3. The reaction mixture was pumped from there back into the small-scale plant reactor. At the temperatures shown in Table 1, the solution was circulated between the small-scale plant reactor, Corning photoreactor and CrO3-PVPy glass column and irradiated for a period of 6 hours, while 1.5 L / h of oxygen was introduced into the Corning photoreactor. During the reaction, up to 69 mg (112 μmol) of TPP was added in batches. At the end of the experiment, the reaction mixture was analyzed without further post-treatment. The results are summarized in Table 1.

[0334] Table 1

[0335]

[0336] 1 Yield relative to the amount of IPA used in the reaction (here 2078.6 mmol)

[0337] # Compound Ia, wherein R 1 =C(O)CH3

[0338] ## A mixture of E isomers and Z isomers of compound Ib, wherein R 1 =C(O)CH3

[0339] Ia # : 1 H-NMR (400MHz, CDCl3): δ = 9.56 (1H), 6.11 (1H), 6.36 (1H), 4.19 (2H), 2.61 (2H), 2.03 (3H)

[0340] Ib## : 1 H-NMR (400MHz, CDCl3): δ = 9.56 (1H), 6.10 (1H), 4.60 (2H), 2.03 (3H), 1.84 (3H)

[0341] 2. Photooxidation of isoprene acetate in an annular gap reactor and simultaneous recrystallization using CrO3-PVPy Drain / dehydration

[0342] Example 4

[0343] equipment:

[0344] Temperature controlled annular gap reactor, volume approximately 500 mL, diameter 40 mm, with displacer 20 mm, layer thickness 10 mm; irradiated from outside to inside;

[0345] LED lamp (2 half shells with a total of 256 LEDs with a wavelength of 420nm and a total radiant power of 86W at 4.2A);

[0346] Harvard syringe pump for replenishing photosensitizer (dissolved in the reaction medium),

[0347] A glass column (d = 3.5 cm) filled with CrO3-PVPy,

[0348] Gear pump, pump head fastest 540mL / min.

[0349] experiment:

[0350] 403.8 g (3151 mmol, 1 eq.) of isoprene acetate (IPA) were placed in a glass bottle, 17.75 g (91.4 mmol, 0.029 eq.) of dimethyl phthalate were added as an NMR internal standard, and 4.0 mg (6.5 μmol, 0.0000021 eq.) of the photosensitizer tetraphenylporphyrin (TPP) were dissolved in the mixture. The reaction mixture was introduced into the apparatus via a dropping funnel and circulated between an irradiated annular gap reactor and a glass column containing 73 g of CrO3-PVPy (loading about 14 wt. % CrO3 relative to the total weight of the supported catalyst), where the hydroperoxides formed were converted into compounds Ia and Ib, where R 1 =C(O)CH3. At 40°C, the solution was irradiated at 420nm for a period of 5 hours while 2L / h of oxygen was introduced into the annular gap reactor from below via a glass frit. During the reaction, 24mg (39μmol) of tetraphenylporphyrin dissolved in the reaction medium were added continuously via a syringe pump depending on the transport. At the end of the experiment, the reaction mixture was analyzed without further post-treatment. The results are summarized in Table 2.

[0351] Table 2

[0352]

[0353] 1 Yield relative to the amount of IPA used in the reaction (here 3151 mmol)

[0354] 3. Photooxidation of isoprene acetate in a double-jacketed reactor and simultaneous recrystallization using CrO3-PVPy Drain / dehydration

[0355] Example 5 and Example 6

[0356] equipment:

[0357] Double jacketed vessel, cylindrical with tempered outer jacket, inner diameter 45 mm, total volume 150 mL (reaction volume approximately 24 mL, corresponding to approximately 18 mm filling height), illuminated from below by 24 LEDs with a wavelength of 405 nm and a total radiant power of 27 W, impeller stirrer.

[0358] experiment:

[0359] 26.3 g (205.27 mmol, 1 eq) of isoprene acetate (IPA) was placed in a glass bottle, 1.22 g (6.28 mmol, 0.031 eq) of dimethyl phthalate was added as an NMR internal standard, and 9.8 mg (15.9 μmol, 0.000078 eq) of photosensitizer tetraphenylporphyrin (TPP) was dissolved in the mixture as a photosensitizer. The reaction mixture was poured into a temperature-controlled double-jacketed container with 5 g of CrO3-PVPy (approximately 12.5 wt % CrO3 was loaded relative to the total weight of the supported catalyst) and stirred at 800 rpm. The solution was irradiated from below at 30 ° C for a period of 4 hours while 2 L / h (Example 7) or 1.5 L / h (Example 8) of oxygen was introduced into the solution. At the end of the experiment, the reaction mixture was analyzed without further post-treatment. The results are summarized in Table 3.

[0360] Table 3

[0361]

[0362] 1 Yield relative to the amount of IPA used in the reaction (here 205.27 mmol)

[0363] Example 7

[0364] equipment:

[0365] Double jacketed vessel, cylindrical with tempered outer jacket, inner diameter 45 mm, total volume 150 mL (reaction volume approximately 24 mL, corresponding to approximately 18 mm filling height), illuminated from below by 24 LEDs with a wavelength of 405 nm and a total radiant power of 27 W, impeller stirrer.

[0366] experiment:

[0367] 23.7g (184.8mmol, 1 equivalent) of isoprene acetate (IPA) was placed in a glass bottle, 1.22g (6.28mmol, 0.034 equivalent) of dimethyl phthalate was added as an NMR internal standard, and 10.0mg (16.3μmol, 0.000088 equivalent) of photosensitizer tetraphenylporphyrin (TPP) was dissolved in the mixture. In addition, 2.62g (17.0mmol, 0.09 equivalent) of carbon tetrachloride was added. The reaction mixture was poured into a temperature-controlled double-jacketed container together with 3.7g of CrO3-PVPy (with respect to the total weight of the supported catalyst, about 12.5 wt% CrO3 was loaded) and stirred at 800rpm. At 30°C, the solution was irradiated from below for a period of 4 hours while 1.5L / h of oxygen was introduced into the solution. At the end of the experiment, the reaction mixture was analyzed without further post-treatment. The results are summarized in Table 4.

[0368] Table 4

[0369]

[0370] 1 Yield relative to the amount of IPA used in the reaction (here 184.8 mmol)

[0371] The yields given above are relative to the amount of starting compound (IPA) used in the reaction. Since the reaction is carried out so that only a relatively small portion of the starting compound reacts (and the remaining portion can further serve as a dispersion medium), the yield based only on the amount of starting material reacted reflects the effectiveness of the reaction. These yields can be calculated by correlating the yields of Ia and Ib with the amount of IPA converted (not shown in the table above).

[0372] 4. Photooxidation of isoprene acetate to isoprene acetate hydroperoxide

[0373] Example 8

[0374] equipment: G1 photoreactor (5 tempered G1 plates, layer thickness approximately 1 mm, each illuminated by LEDs on both sides, a total of 200 LEDs with a wavelength of 405 nm and a total radiant power of 195 W), 100 mL small device reactor, impeller stirrer, gear pump.

[0375] experiment:

[0376] In a 100 mL mini-unit reactor, a mixture of 135.0 g (1053.3 mmol, 1 eq) of isoprene acetate (IPA) and 6.22 g (32.0 mmol, 0.03 eq) of dimethyl phthalate as an NMR internal standard was prepared, and 15 mg (24.7 μmol, 0.000023 eq) of tetraphenylporphyrin as a photosensitizer was dissolved in the mixture. The reaction solution was stirred at 100 rpm and pumped in a loop to The solution was irradiated at the temperature indicated in Table 5 for a period of 6 hours while 3 L / h of oxygen was introduced at 1.7 bar to 2.4 bar. The reaction was terminated before the complete conversion of isoprene acetate (the conversions of the experiment are listed in Table 5). At the end of the experiment, the reaction mixture was analyzed without further workup. The results are summarized in Table 5.

[0377] Table 5

[0378]

[0379] 1 Yield relative to the amount of IPA used in the reaction (here 1053.3 mmol)

[0380] + Compound III.a, wherein R 1 =-C(O)CH3

[0381] III.a + : 1 H-NMR (500MHz, CDCl3): δ=5.19(1H),5.10(1H),4.47(2H),4.26(2H),2.47(2H),2.06(3H)

[0382] 13 C-NMR (125MHz, CDCl3): δ=171.19(s), 140.75(s), 116.58(t), 79.82(t), 62.69(t), 32.36(t), 22.34(q)

[0383] In addition, compound III.c was identified, where R1 =-C(O)CH3, which is assumed to be the result of further photooxidation of compound III.b competing with the conversion of III.b to Ib, or directly the result of (double) photooxidation of II.a:

[0384] III.c + : 1 H-NMR (700MHz, CDCl3): δ=5.45(1H),5.41(1H),4.71(1H),4.55(2H),4.39(2H),2.09(3H)

[0385] 13 C-NMR (175MHz, CDCl3): δ = 170.6 (s), 139.8 (s), 120.2 (t), 83.3 (d), 77.8 (t), 62.7 (t), 21.1 (q)

[0386] 5. Photooxidation of isoprenol to isoprenol hydroperoxide

[0387] Example 9

[0388] equipment: G1 photoreactor (5 tempered G1 plates, layer thickness approximately 1 mm, each illuminated by LEDs on both sides, a total of 200 LEDs with a wavelength of 610 nm and a total radiant power of 83 W), 100 mL small device reactor, impeller stirrer, gear pump.

[0389] experiment:

[0390] In a 100 mL small-scale reactor, 135.0 g (1567.4 mmol, 1 equivalent) of isoprenol (IP; Compound II.a, wherein R 1 The reaction solution was stirred at 300 rpm and pumped to a reactor at 100 mL / min in a loop. The solution was irradiated for a period of 4 hours at 30°C while 3 L / h of oxygen was introduced into the reactor at 5 bar. The reaction mixture was stirred for 2 h in 4% ethanol and then stirred for 2 h in 80% ethanol. The reaction mixture was ...

[0391] Table 6

[0392]

[0393] 1 Yield relative to the amount of IP used in the reaction (here 1567.4 mmol)

[0394] ++ Compound III.a, wherein R 1 =H

[0395] ### Compound Ia, wherein R 1 =H

[0396] III.a ++ : 1 H-NMR (400MHz, CDCl3): δ=5.24(1H),5.16(1H),4.47(2H),3.86(2H),2.41(2H)

[0397] Example 10

[0398] Equipment: Double-jacketed vessel, cylindrical with tempered outer jacket, inner diameter 45 mm, total volume 150 mL (reaction volume approximately 38 mL, corresponding to approximately 24 mm filling height), illuminated from below by 24 LEDs with a wavelength of 405 nm and a total radiant power of 27 W, impeller stirrer.

[0399] experiment:

[0400] In a 50 mL glass vial, a mixture of 30.0 g (348.3 mmol, 1 eq.) isoprenol (IP), 1.39 g (7.2 mmol, 0.021 eq.) dimethyl phthalate and 1.5 g (12.5 mmol, 0.036 eq.) chloroform as an NMR internal standard was prepared, and 4.6 mg (7.5 μmol, 0.000021 eq.) tetraphenylporphyrin as a photosensitizer was dissolved in the mixture. The reaction solution was poured into a temperature-controlled double-jacketed container and stirred at 800 rpm. The solution was irradiated at 10° C. for a period of 5 hours while 2 L / h of oxygen was introduced into the solution. During the reaction, another 8.2 mg (13.3 μmol) of photosensitizer was added in batches. The reaction was clearly terminated before the complete conversion of isoprenol (the conversion rates of the experiments are listed in Table 7). At the end of the experiment, the reaction mixture was analyzed without further post-treatment. The results are summarized in Table 7.

[0401] Table 7

[0402]

[0403] 1 Yield relative to the amount of IP used in the reaction (here 348.3 mmol)

Claims

1. A process for preparing a compound of formula Ia or Ib or a mixture thereof, or a stereoisomer of said compound Ia or Ib, or a mixture of different stereoisomers of said compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, in R 1 is hydrogen or -C(=O)R 2 ;and R 2 It is C1-C 20 -alkyl; The method comprises: (i) providing a reaction mixture comprising a compound of formula II.a, a photosensitizer and optionally a transition metal catalyst: Where R 1 As defined above; (ii) passing an oxygen-containing gas through the reaction mixture provided in step (i) while irradiating the reaction mixture with light; (iii) contacting the reaction mixture of or obtained in step (ii) with a transition metal catalyst if a transition metal catalyst has not already been provided in step (i); (iv.1) if desired, after completion of the reaction, isolating the one or more compounds (Ia) or (Ib) obtained in step (ii) or (iii); and (v.1) if desired, hydrolyzing the one or more compounds (Ia) or (Ib) isolated in step (iv.1) to form compounds (Ia) or (Ib) wherein R 1 It is hydrogen; or (iv.2) if desired, hydrolyzing the reaction mixture obtained in step (ii) or (iii); and (v.2) if desired, isolating the one or more compounds (Ia) or (Ib) obtained in step (iv.2).

2. The method according to claim 1, wherein R 2 is C1-C4-alkyl or n-C 15 -alkyl.

3. The method according to claim 2, wherein R 2 is C1-C4-alkyl, preferably methyl.

4. A process according to any one of the preceding claims, wherein the transition metal catalyst used in step (i) or (iii) is a heterogeneous catalyst, preferably a supported heterogeneous catalyst, wherein the support material is preferably selected from the group consisting of carbon, alumina, silica, zeolites and organic polymers.

5. The method according to claim 4, wherein the heterogeneous transition metal catalyst comprises at least one salt or oxide of a transition metal from Group 4 to Group 12 of the Periodic Table of Elements, The heterogeneous transition metal catalyst is preferably a supported catalyst, which comprises at least one salt or oxide of a transition metal from Group 4 to Group 12 of the periodic table supported on a support material, wherein the support material is preferably selected from the group consisting of carbon, alumina, silica, zeolite and an organic polymer.

6. The method according to claim 5, wherein the salt or oxide of the transition metal is a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of a transition metal from Group 4 to Group 12, Period 4 of the Periodic Table of the Elements, or is a chromate, chlorochromate, dichromate or permanganate; wherein the salt or oxide of the transition metal is preferably a C2-C8-carboxylate, halide, nitrate, phosphate, sulfate, chlorate, perchlorate or oxide of Cu, Cr, Fe or Ni, or a chromate or dichromate, preferably an alkali metal, Zn or Fe chromate or dichromate; The salt or oxide of the transition metal is more preferably selected from the group consisting of Cu(II) acetate, Cu(ClO4)2, CuCl2, CuO, Co(II) acetate, CrO3 and alkali metal dichromates, preferably K2Cr2O7.

7. The method according to claim 6, wherein the salt or oxide of the transition metal is Cr(VI) oxide CrO3.

8. A process according to any one of the preceding claims, wherein the transition metal catalyst used in step (i) or (iii) is a supported heterogeneous catalyst, wherein the support material is an organic polymer, wherein the organic polymer is selected from the group consisting of vinylpyridine homopolymers and copolymers, N-vinylpyrrolidine homopolymers and copolymers, styrene homopolymers and copolymers, polyurethanes, acrylate homopolymers and copolymers and methacrylate homopolymers and copolymers, wherein the organic polymer is preferably selected from the group consisting of vinylpyridine homopolymers and copolymers.

9. The method of claim 8, wherein the organic polymer is selected from the group consisting of 2-vinylpyridine homopolymers and copolymers, 4-vinylpyridine homopolymers and copolymers, and N-vinylpyrrolidine homopolymers and copolymers; The organic polymer is preferably selected from the group consisting of poly(2-vinylpyridine); poly(4-vinylpyridine); copolymers of 2-vinylpyridine and methyl methacrylate, preferably block copolymers; and poly(N-vinylpyrrolidine), and more preferably selected from polyvinylpyridine, especially poly(4-vinylpyridine).

10. The method according to any one of the preceding claims, wherein the transition metal is Cr(VI) oxide CrO3 on polyvinylpyridine, preferably on poly(4-vinylpyridine).

11. The method according to any one of the preceding claims, wherein the photosensitizer is selected from the group consisting of: fluorescein, eosin, rose bengal, erythrosine, tetraphenylporphyrin, tetraphenylporphyrin cobalt, tetraphenylporphyrin zinc, hematoporphyrin, rhodamine B, Besickel's brilliant red, methyl violet, methylene blue, fullerene C 60 , Fullerene C 70 , graphene, carbon nanotubes, Ru(bpy)3 2+ Salt, Ru(phen)3 2+ Salts, cercosporin, hypocrellin-A and mixtures thereof; The photosensitizer is preferably selected from the group consisting of tetraphenylporphyrin, tetraphenylporphyrin cobalt, tetraphenylporphyrin zinc, methylene blue, Ru(bpy)3 2+ Salt and Ru(phen)3 2+ Salt.

12. The method of claim 11, wherein the photosensitizer is selected from the group consisting of tetraphenylporphyrin, tetraphenylporphyrin zinc, and Ru(bpy)3 2+ Salts, and preferably tetraphenylporphyrin.

13. The method according to any one of the preceding claims, wherein in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 350 nm to 800 nm, preferably in the range of 350 nm to 680 nm, more preferably in the range of 400 nm to 650 nm, even more preferably in the range of 400 nm to 580 nm, in particular in the range of 400 nm to 500 nm, preferably monochromatic light.

14. The method according to any one of claims 11 to 13, wherein the photosensitizer is tetraphenylporphyrin, tetraphenylporphyrin cobalt or tetraphenylporphyrin zinc, and in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 400 nm to 430 nm, preferably 400 nm to 420 nm, preferably monochromatic light; or the photosensitizer is methylene blue, and in step (ii), the reaction mixture is irradiated with light having a wavelength in the range of 600 nm to 620 nm, preferably monochromatic light, or the photosensitizer is Ru(bpy)3 2+ Salt or Ru(phen)3 2+ salt, and in step (ii), irradiating the reaction mixture with light, preferably monochromatic light, having a wavelength in the range of 450 nm to 480 nm, preferably 460 nm to 475 nm.

15. A method according to any one of the preceding claims, wherein the oxygen-containing gas used in step (ii) is selected from the group consisting of oxygen, air and a mixture of oxygen and nitrogen, the mixture containing oxygen in a range of 1 wt % to 99 wt % relative to the gross weight of the mixture, wherein the oxygen-containing gas used in step (ii) is preferably oxygen.

16. A method according to any one of the preceding claims, wherein Steps (ii) and (iii) are performed neat; or Steps (ii) and (iii) are carried out in the presence of a chlorinated C1-C2-alkane, wherein the molar ratio of the compound (II.a) provided in step (i) to the chlorinated C1-C2-alkane is 50:1 to 1:1.5, preferably 20:1 to 1:1, more preferably 15:1 to 2:

1.

17. A hydroperoxide compound of formula III.a, III.b or III.c, or a stereoisomer of said compound of formula III.a, III.b or III.c, or a mixture of different stereoisomers of said compound III.a, III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c: in In compound III.a, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl; In compound III.b, R 1 Yes-C(=O)R 2 ; and R 2 It is C1-C 20 -alkyl; and In compound III.c, R 1 is hydrogen or -C(=O)R 2 ; and R 2 It is C1-C 20 - alkylalkyl; Preferred are hydroperoxide compounds of the formula III.a or III.b, or stereoisomers of said compounds of the formula III.a or III.b, or mixtures of different stereoisomers of said compounds III.a and / or III.b, or mixtures of different compounds III.a and / or III.b.

18. Use of a hydroperoxide compound of formula III.a, III.b or III.c, or a stereoisomer of a compound of formula III.a, III.b or III.c, or a mixture of different stereoisomers of compounds III.a, III.b and / or III.c, or a mixture of different compounds III.a, III.b and / or III.c, according to claim 17, wherein R 1 It can also be hydrogen, preferably the use of a hydroperoxide compound of formula III.a or III.b according to claim 17, or a stereoisomer of a compound of formula III.a or III.b, or a mixture of different stereoisomers of the compound III.a and / or III.b, or a mixture of different compounds III.a and / or III.b, wherein, however, in compound III.b R 1 It may also be hydrogen; it is used as an intermediate in the synthesis of a compound of formula Ia or Ib according to any one of claims 1 to 3, or a stereoisomer of the compound Ia or Ib, or a mixture of different stereoisomers of the compound Ia and / or Ib, or a mixture of different compounds Ia and / or Ib, or as an intermediate in the synthesis of retinol, its stereoisomers, its derivatives, or stereoisomers of its derivatives, wherein the derivative of retinol is preferably selected from the group consisting of: retinol esters, retinal and retinoic acid.

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