A triphenylamine-mediated photocatalytic isomerization of alkenes e to z

Abstract

This invention discloses a triphenylamine-mediated photocatalytic isomerization method for olefins from E to Z, belonging to the field of organic synthesis technology. This invention uses triphenylamine and 4-nitrotriphenylamine, triphenylamine compounds, as photocatalysts to catalyze the E-Z isomerization of olefins. Their molecular structures have a propeller configuration, which can drive olefin configuration inversion through triplet energy transfer without the need for metal participation, achieving low-cost, highly stable, and mild E-Z isomerization of olefins. This invention is carried out at room temperature, without the need for high temperature and pressure, resulting in low energy consumption and environmental friendliness. It has a wide substrate applicability, exhibiting good catalytic activity for olefins with different substituents such as methyl, halogen, cyano, and hydroxyl groups, with product yields reaching up to 92%. The operation is simple, the reaction process is straightforward, and it is suitable for large-scale production applications.

Description

Technical Field

[0001] This invention belongs to the field of organic synthesis technology, and particularly relates to a triphenylamine-mediated photocatalytic isomerization method for olefins E to Z. Background Technology

[0002] Z-olefins are an important class of molecular skeletons in medicinal chemistry, materials chemistry, and synthetic chemistry, and are widely found in natural products, drug molecules, and functional materials. Therefore, developing efficient and highly selective E→Z olefin isomerization methods has significant research value and application prospects.

[0003] Current cis-trans isomerization methods for olefins mainly rely on noble metal complex catalysts (such as iridium and ruthenium complexes) or natural / dye molecules with structures that are difficult to directionally modify (such as eosin Y, vitamin B compounds, and fluorescent orange-red), achieving conversion through a triplet energy transfer mechanism under light conditions. However, both of these systems have significant limitations: on the one hand, iridium and ruthenium are both noble metals, and their chloride raw materials are expensive, directly leading to increased costs for catalyst preparation and application, and the triplet energy of these noble metal complexes is difficult to precisely control; on the other hand, molecules such as eosin Y, vitamin B compounds, and fluorescent orange-red have complex structures, making it difficult to directionally introduce target functional groups at specific sites, resulting in fixed triplet energies that cannot be adapted to a wide range of substrate types. Therefore, there is an urgent need for a low-cost, highly stable, and mild photocatalytic olefin E→Z isomerization method to solve the problems of high catalyst cost and difficulty in directionally modifying existing catalysts. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a triphenylamine-mediated photocatalytic isomerization method for olefins E to Z.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a triphenylamine-mediated photocatalytic isomerization method for olefins from E to Z, comprising the following steps: mixing an E-type olefin, a triphenylamine-based photocatalyst, and an organic solvent under an inert gas atmosphere, then carrying out an isomerization reaction under light irradiation, and obtaining a Z-type olefin after separation and purification; The triphenylamine photocatalyst is selected from triphenylamine and / or 4-nitrotriphenylamine.

[0006] Furthermore, the E-type olefin includes one or more of E-stilbene, p-methyl-substituted E-stilbene, halogen-substituted E-stilbene, E-β-methylstyrene, cyano-substituted E-styrene, and hydroxy-substituted E-styrene.

[0007] Furthermore, the amount of the triphenylamine photocatalyst is 5% to 15% of the molar amount of the E-type olefin.

[0008] Furthermore, the organic solvent is selected from acetone and / or acetonitrile; based on the amount of E-type olefin used being 1 mmol, the amount of the organic solvent used is 5~25 mL.

[0009] Furthermore, the light source is an LED light source; the wavelength of the LED light source is 395nm~450nm.

[0010] Furthermore, the isomerization reaction is carried out at room temperature for 6 to 16 hours.

[0011] Furthermore, the inert gas is nitrogen.

[0012] Furthermore, the separation and purification method involves rotary evaporation concentration followed by column chromatography separation.

[0013] Compared with the prior art, the present invention has the following advantages and technical effects: This invention uses triphenylamine and 4-nitrotriphenylamine, triphenylamine compounds, as photocatalysts to catalyze the E-Z isomerization of olefins. Their molecular structures have a propeller configuration, which can drive the configuration inversion of olefins through triplet energy transfer without the participation of metals, thus achieving the low-cost, high-stability, and mild reaction conditions for the E→Z isomerization of olefins.

[0014] This invention uses triphenylamine or its derivatives as a metal-free photocatalyst, which is low in cost, highly stable, and easy to chemically modify, overcoming the cost and environmental problems of traditional metal catalysts. The reaction is carried out at room temperature with LEDs as the light source, eliminating the need for high temperature and high pressure, resulting in low energy consumption and environmental friendliness. It has a wide range of substrate applications, exhibiting good catalytic activity for alkenes with different substituents such as methyl, halogen, cyano, and hydroxyl groups, with product yields reaching up to 92%. The operation is simple, the reaction process is straightforward, and it is easy to scale up for production and application. Attached Figure Description

[0015] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a traditional application area for triphenylamine; Figure 2 This is a schematic diagram of the reaction process in which triphenylamine is used as a photocatalyst for the E→Z isomerization of olefins in this invention; Figure 3 The HOMO-LUMO energy level difference, electron cloud distribution from ground state to excited state, and structural formulas of triphenylamine, 4-methyltriphenylamine, 4-methoxytriphenylamine, and 4-nitrotriphenylamine; Figure 4The S1-S0 and T1-S0 energy differences of triphenylamine, 4-methyltriphenylamine, 4-methoxytriphenylamine, 4-nitrotriphenylamine, E-stilbene, and E-β-methylstyrene; Figure 5 S is the reaction system in Examples 1 and 7. n and T n State-electron coupling energy, the left figure is Example 1, and the right figure is Example 7; Figure 6 The energy change (a) of the 4-nitrotriphenylamine-catalyzed E-stilbene isomerization in Example 1, and the geometry and energy of the E-stilbene transition state (b). Figure 7 For product 2a in Example 1 1 H NMR spectrum; Figure 8 For product 2a in Example 1 13 C10 NMR spectrum. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] This invention provides a triphenylamine-mediated photocatalytic isomerization method for olefins E to Z, comprising the following steps: mixing E-type olefins, triphenylamine photocatalysts, and organic solvents under an inert gas atmosphere, and then carrying out an isomerization reaction under light irradiation, followed by separation and purification to obtain Z-type olefins; The triphenylamine photocatalyst is selected from triphenylamine (Cat 1) and / or 4-nitrotriphenylamine (Cat 4).

[0019] Traditional applications of triphenylamine are seen in... Figure 1 The process of using triphenylamine as a photocatalyst for the E→Z isomerization of olefins in this invention is described below. Figure 2It can be seen that the traditional application fields of triphenylamine include solar cells, metal-organic framework materials, organic covalent materials, and chromophore polymers, but there are no reports on the application of triphenylamine in the field of photocatalysts. This invention uses triphenylamine as a photocatalyst to drive olefin configuration inversion through triplet energy transfer, realizing the low-cost, high-stability, and mild reaction conditions of olefin E→Z isomerization.

[0020] The reaction mechanism of triphenylamine-mediated photocatalytic isomerization of olefins E to Z in this invention is as follows: (1) Photoexcitation process: Triphenylamine photocatalysts are excited to the singlet excited state (S1) under light irradiation, and then transformed into the triplet excited state (T1) through intersystem crossing (ISC). (2) Energy transfer process: The photocatalyst in the triplet excited state transfers energy to the E-olefin through triplet energy transfer, causing the E-olefin to transition from the ground state (S0) to the triplet state (T1), while the photocatalyst returns to the ground state; (3) Isomerization process: E-type olefins in the triplet state undergo configuration inversion to form Z-type olefins, and then return from the triplet state to the ground state (S0).

[0021] In a preferred embodiment, the E-type olefin includes one or more of E-stilbene, p-methyl-substituted E-stilbene, halogen-substituted E-stilbene, E-β-methylstyrene, cyano-substituted E-styrene, and hydroxy-substituted E-styrene; the halogen-substituted E-stilbene is selected from E-4-bromostilbene, and the cyano-substituted E-styrene is selected from E-cinnamonitrile.

[0022] In a preferred embodiment, when the E-olefin is E-stilbene, p-methyl-substituted E-stilbene, or halogen-substituted E-stilbene, the triphenylamine photocatalyst is selected from 4-nitrotriphenylamine; when the E-olefin is E-β-methylstyrene, cyano-substituted E-styrene, or hydroxyl-substituted E-styrene, the triphenylamine photocatalyst is selected from triphenylamine.

[0023] In a preferred embodiment, the amount of the triphenylamine photocatalyst is 5% to 15% of the molar amount of the E-type olefin, more preferably 5% to 10%, and even more preferably 10%. When the amount of the triphenylamine photocatalyst is within the above range, the yield of the Z-type product increases with the increase of the amount of photocatalyst. Further increasing the amount of photocatalyst from 10% does not significantly improve the yield of the Z-type product. Therefore, the amount of the triphenylamine photocatalyst is preferably 10%.

[0024] In a preferred embodiment, the organic solvent is selected from acetone and / or acetonitrile, and more preferably acetone.

[0025] In a preferred embodiment, based on an E-type olefin dosage of 1 mmol, the amount of organic solvent used is 5-25 mL, more preferably 10 mL.

[0026] In a preferred embodiment, the light source is an LED light source; the wavelength of the LED light source is 395nm~450nm, more preferably 450nm.

[0027] In a preferred embodiment, the isomerization reaction is carried out at room temperature for 6 to 16 hours, more preferably 12 hours.

[0028] In a preferred embodiment, the inert gas is nitrogen; the reaction system further includes a step of purging with nitrogen for 5 to 15 minutes before the isomerization reaction to remove air; the nitrogen purging time is further preferably 10 minutes.

[0029] In a preferred embodiment, the separation and purification method is to concentrate by rotary evaporation followed by column chromatography separation.

[0030] In this embodiment of the invention, room temperature refers to "25±2℃".

[0031] Unless otherwise specified, all raw materials used in the embodiments of this invention were purchased through commercial channels.

[0032] Example 1 The isomerization method for E-stilbene involves the following steps: In a clean photocatalytic reaction flask, 36.0 mg (0.2 mmol) of E-stilbene and 4-nitrotriphenylamine (Cat 4, 10 mol%) were added, followed by the addition of 2 mL of acetone via syringe to obtain the reaction mixture. The reaction mixture was purged with nitrogen for 10 min to remove air, and the reaction flask was sealed and placed under a 450 nm LED light source at room temperature for 12 h. After the reaction was completed, the reaction solution was concentrated by rotary evaporation, and the crude product was separated by column chromatography to obtain Z-stilbene (2a) with a yield of 91%.

[0033] Characterization of Z-stilbene: 1 H NMR (400 MHz, CDCl3) δ 7.16~7.12 (m, 10H), 6.51 (s, 2H); 13 C NMR (101 MHz, CDCl3) δ 137.29, 130.30, 128.93, 128.26, 127.14.

[0034] Comparative Example 1 The isomerization method for E-stilbene differs from that in Example 1 only in that 4-nitrotriphenylamine is replaced with 4-methyltriphenylamine (Cat 2, 10 mol%), otherwise it is the same as in Example 1.

[0035] Comparative Example 2 The isomerization method for E-stilbene differs from that in Example 1 only in that 4-nitrotriphenylamine is replaced with 4-methoxytriphenylamine (Cat 3, 10 mol%), otherwise it is the same as in Example 1.

[0036] Example 2 The isomerization method for E-stilbene differs from that in Example 1 only in that acetone is replaced with an equal volume of acetonitrile; otherwise, it is the same as in Example 1.

[0037] Example 3 The isomerization method for E-stilbene differs from that in Example 1 only in that the amount of 4-nitrotriphenylamine used is 5 mol%, otherwise it is the same as in Example 1.

[0038] Example 4 The isomerization method for E-stilbene differs from that in Example 1 only in that the amount of 4-nitrotriphenylamine used is 15 mol%, otherwise it is the same as in Example 1.

[0039] Example 5 The isomerization method for E-stilbene differs from that in Example 1 only in that it is reacted at room temperature for 12 hours under a 395nm LED light source; otherwise, it is the same as in Example 1.

[0040] The yields of the products in Comparative Examples 1-2 and Examples 2-5 are shown in Table 1.

[0041] Table 1 As shown in Table 1, the yield of Z-stilbene was significantly higher when using 4-nitrotriphenylamine as a catalyst than when using other triphenylamine derivatives; the yield was higher with acetone as a solvent than with acetonitrile; the yield increased with a catalyst dosage of 5 mol% to 10 mol%, but there was no significant increase in yield when the catalyst dosage was further increased to 15 mol%; the yield was higher with 450 nm LED light source than with 395 nm LED light source.

[0042] Example 6 The isomerization method for p-methyl-substituted E-stilbene involves the following steps: In a clean photocatalytic reaction flask, 38.9 mg (0.2 mmol) of p-methyl-substituted E-stilbene and 4-nitrotriphenylamine (Cat 4, 10 mol%) were added, followed by the addition of 2 mL of acetone via syringe to obtain the reaction mixture. The reaction mixture was purged with nitrogen for 10 min to remove air, and the reaction flask was sealed and placed under a 450 nm LED light source at room temperature for 12 h. After the reaction was completed, the reaction solution was concentrated by rotary evaporation, and the crude product was separated by column chromatography to obtain p-methyl-substituted Z-stilbene (2b) with a yield of 89%.

[0043] Characterization of p-methyl-substituted Z-stilbene: 1 H NMR (400 MHz, CDCl3) δ 7.16~7.14 (m, 4H), 7.03~7.01 (m, 4H), 6.50 (s, 2H), 2.30 (s, 6H); 13 C NMR (101 MHz, CDCl3) δ 136.77, 134.57, 129.58, 128.95, 128.82.

[0044] Example 7 The isomerization method for E-β-methylstyrene involves the following steps: In a clean photocatalytic reaction flask, 23.6 mg (0.2 mmol) of E-β-methylstyrene and triphenylamine (Cat1, 10 mol%) were added, followed by the addition of 2 mL of acetone via syringe to obtain the reaction mixture. The reaction mixture was purged with nitrogen for 10 min and then sealed. The mixture was placed under a 450 nm LED light source and reacted at room temperature for 12 h. After the reaction was completed, the reaction solution was concentrated by rotary evaporation, and the crude product was separated by column chromatography to obtain Z-β-methylstyrene (2c), with a yield of 39%.

[0045] Characterization of Z-β-methylstyrene: 1 H NMR (400 MHz, CDCl3) δ 7.35~7.28 (m, 4H), 7.23~7.19 (m, 1H), 6.45~6.42 (d, J=12Hz, 1H), 5.83~5.75 (m, 1H), 1.91~1.89 (d, J=8Hz, 3H); 13 C NMR (101MHz, CDCl3) δ 137.64, 129.88, 128.87, 128.16, 126.84, 126.45, 14.69.

[0046] Figure 3 The HOMO-LUMO energy level differences, electron cloud distributions from the ground state to the excited state, and structural formulas of triphenylamine, 4-methyltriphenylamine, 4-methoxytriphenylamine, and 4-nitrotriphenylamine are presented. Figure 3It can be seen that the E values ​​of triphenylamine (Cat 1), 4-methyltriphenylamine (Cat 2), 4-methoxytriphenylamine (Cat 3), and 4-nitrotriphenylamine (Cat 4) are... （HOMO-LUMO） The values ​​were 4.91 eV, 4.85 eV, 4.74 eV, and 3.71 eV, respectively, with 4-nitrotriphenylamine having an EV of 4-nitrotriphenylamine. （HOMO-LUMO） The lowest value indicates that it is most easily photoexcited to reach the excited state. Therefore, this invention selects 4-nitrotriphenylamine as the photocatalyst for diarylolefins.

[0047] Figure 4 The S1-S0 and T1-S0 energy differences are for triphenylamine, 4-methyltriphenylamine, 4-methoxytriphenylamine, 4-nitrotriphenylamine, E-stilbene, and E-β-methylstyrene. Figure 4 As can be seen, triphenylamine has the highest triplet energy, and therefore it can activate a wider range of substrates through energy transfer. Therefore, this invention selects triphenylamine as a photocatalyst for arylalkyl olefins.

[0048] Figure 5 S is the reaction system in Examples 1 and 7. n and T n Electron coupling energy, the left figure is Example 1, and the right figure is Example 7. From Figure 5 It can be seen that 4-nitrotriphenylamine can successfully transfer energy to stilbene, and triphenylamine can also effectively activate methylstyrene.

[0049] Figure 6 The energy change (a) and the geometry and energy of the E-stilbene transition state catalyzed by 4-nitrotriphenylamine in Example 1 are shown in Figure 1. Figure 6 It can be seen that triphenylamine can activate olefins through energy transfer, thereby promoting the conversion of trans-olefins to cis-olefins.

[0050] Figure 7 For product 2a in Example 1 1 H NMR spectrum. Figure 8 For product 2a in Example 1 13 C10 NMR spectrum. From Figure 7 and Figure 8 It can be seen that Z-stilbene was successfully synthesized in Example 1.

[0051] Example 8 Substrate suitability test: The isomerization method for E-olefins differs from that in Example 1 only in that E-stilbene is replaced with equimolar amounts of E-4-bromostilbene or E-cinnamonitrile, while the rest is the same as in Example 1.

[0052] The results of the isomerization reactions of different substituted olefins in Example 8 are shown in Table 2.

[0053] Table 2 The results in Table 2 show that the method of the present invention has good compatibility with olefin substrates containing different functional groups, and exhibits excellent catalytic activity, especially for stilbene substrates.

[0054] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A triphenylamine-mediated photocatalytic isomerization method for olefins E to Z, characterized in that, Includes the following steps: Under an inert gas atmosphere, E-type olefins, triphenylamine photocatalysts, and organic solvents are mixed and then subjected to an isomerization reaction under light irradiation. After separation and purification, Z-type olefins are obtained. The triphenylamine photocatalyst is selected from triphenylamine and / or 4-nitrotriphenylamine.

2. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The E-type olefins include one or more of E-stilbene, p-methyl-substituted E-stilbene, halogen-substituted E-stilbene, E-β-methylstyrene, cyano-substituted E-styrene, and hydroxyl-substituted E-styrene.

3. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The amount of the triphenylamine photocatalyst used is 5% to 15% of the molar amount of the E-type olefin.

4. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The organic solvent is selected from acetone and / or acetonitrile; the amount of organic solvent used is 5 to 25 mL, based on 1 mmol of E-type olefin.

5. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The light source is an LED light source; the wavelength of the LED light source is 395nm~450nm.

6. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The isomerization reaction is carried out at room temperature for 6 to 16 hours.

7. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The inert gas is nitrogen.

8. The triphenylamine-mediated photocatalytic isomerization method for olefins E to Z according to claim 1, characterized in that, The separation and purification method is to concentrate by rotary evaporation followed by column chromatography separation.

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