A Schiff base aluminum compound and its preparation and application in hydroboration of alkynes

Abstract

The present invention discloses a Schiff base aluminum compound, its preparation method, and its application in the hydroboration of alkynes. The preparation method comprises the following steps: first, 2-aminopyridine and salicylaldehyde are condensed to form a Schiff base ligand, which is then reacted with an equal amount of diisobutylaluminum hydride to form an aluminum compound. The preparation method is simple, and the synthesized Schiff base aluminum compound exhibits significant efficacy in the hydroboration of alkynes. Only 5% of the catalyst is required, resulting in a fast reaction rate and high yield, in line with the concept of green chemistry.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic reactions of aluminum metal compounds, and in particular to a Schiff base aluminum compound, a preparation method thereof, and application thereof in alkyne hydroboration reactions. Background Art

[0002] Organoborane compounds are a versatile class of synthetic intermediates that can undergo a wide range of organic transformations. Hydroboration, the direct addition of BH bonds to various unsaturated bonds, is a powerful tool for preparing organoborane derivatives. Organoboron compounds generated by hydroboration are important organic intermediates in various chemical transformations and material syntheses. They can be further converted into a variety of compounds, holding significant significance in modern industrial chemistry and academic research. Organoboron compounds are key and versatile precursors in carbon-carbon and carbon-heteroatom bonding reactions, such as the Suzuki-Miyaura reaction and the Chan-Lam cross-coupling reaction.

[0003] Many natural products contain di- or tri-substituted olefin building blocks with specific configurations. Researchers are striving to explore more efficient pathways for the stereoselective synthesis of multifunctional olefin compounds with specific configurations. An important class of these compounds is olefin boranes, which possess unique reactivity and serve as crucial intermediates in organic synthesis. Hydroboration of alkynes is a highly effective method for preparing olefin boranes and polysubstituted olefins. Currently, transition-metal-catalyzed addition reactions of organic boronic acids to unsaturated bonds are the primary method for preparing olefin boranes. The catalysts used are primarily transition metal complexes such as Rh, Ru, Mo, and Ti. Hydroboration of alkynes using main-group metals as catalysts is relatively rare, particularly aluminum compounds. To date, no reports have been published on hydroboration of alkynes catalyzed by Schiff-base aluminum compounds. Summary of the Invention

[0004] Objectives of the Invention: To address the shortcomings of the prior art, the present invention provides a Schiff-base aluminum compound suitable for use in the hydroboration of alkynes. Another objective of the present invention is to provide a method for preparing the Schiff-base aluminum compound. Yet another objective of the present invention is to provide the use of the Schiff-base aluminum compound in the hydroboration of alkynes.

[0005] Technical solution: In order to achieve the above-mentioned purpose of the invention, the technical solution adopted by the present invention is:

[0006] A Schiff base aluminum compound: The specific structure is as follows

[0007]

[0008] A method for preparing a Schiff base aluminum compound comprises the following steps:

[0009] (1) Under nitrogen protection, 2, acetone, p-methylaminopyridine, salicylic aldehyde and hydrochloric acid are refluxed in a methanol solvent at a molar ratio of 1:1:0.001 for 4 hours. After the reaction is completed, water is added to precipitate yellow crystals, which are filtered, washed with a small amount of ice methanol and then dried to obtain a solid which is the Schiff base ligand.

[0010] (2) In anhydrous and oxygen-free environment, under nitrogen protection, in a Schlenk reaction flask, diisobutylaluminum hydride is slowly added dropwise to the toluene solution of the above-mentioned ligand at low temperature, with a molar ratio of 1:1. The mixture is stirred at room temperature overnight, allowed to stand and filtered, and then the toluene is concentrated and placed in a low-temperature refrigerator to obtain a large amount of crystals the next day, which are Schiff base aluminum compounds.

[0011] The reaction formula of the appeal method is as follows:

[0012]

[0013] Application of the Schiff base aluminum compound in alkyne hydroboration reaction.

[0014] The use of a Schiff base aluminum compound in catalyzing the hydroboration reaction of an alkyne with borane comprises the following steps:

[0015] Under anhydrous and oxygen-free conditions and under nitrogen protection in a glove box, a Schiff base aluminum compound was added to a Schlenk flask of approximately 10 ml, and then a corresponding proportion of borane was added and mixed evenly. Finally, alkyne was added, and then heated at 60°C for 10 hours. The reaction was then terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as an elution system to obtain a vinyl borane compound.

[0016] In the above technical solution, the alkyne is selected from one of aromatic alkynes and aliphatic alkynes; the chemical structure of the aromatic aldehyde is

[0017]

[0018] Wherein R is hydrogen, halogen, methyl or trifluoromethyl.

[0019] The aliphatic alkyne is 1-ethynylcyclohexene or 1-heptyne.

[0020] The borane is pinacol borane.

[0021] The amount of the catalyst used is 5% of the molar number of the alkyne, the molar ratio of borane to alkyne is 1:1, the reaction temperature is 60° C., and the reaction time is 10 hours.

[0022] The above reaction formula is as follows:

[0023]

[0024] Wherein, R1 and R2 are derived from the selected alkyne.

[0025] Beneficial effects: Compared with the prior art, the present invention has the following advantages

[0026] 1) This invention is the first to use a Schiff base compound to catalyze the reaction of alkynes with pinacol borane to synthesize boronic acid alkenes. This is also the first time that Schiff base compounds have been applied to catalysis. Their extremely high catalytic activity, simple structure, and ease of synthesis not only enrich the preparation of boronic acid alkenes through the hydroboration reaction of alkynes with boranes, but also provide a new solution and expand the application of Schiff base compounds.

[0027] 2) The Schiff base aluminum compound of the present invention can catalyze the hydroboration of alkynes and boranes with high activity under mild conditions, requiring only 5% of the molar amount of the substrate. Compared to several catalysts reported in the literature, the reaction is very fast, achieving nearly 100% conversion. The mild reaction conditions and simple, controllable reaction are highly consistent with the concept of green chemistry. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1

[0030] 1) Preparation of Schiff base ligands

[0031] Under nitrogen protection, add 100 mL of anhydrous methanol to a 250 mL round-bottom flask, then add 40 mmol of 2-aminopyridine, 40 mmol of salicylaldehyde and 0.04 mmol of hydrochloric acid, and reflux at 70 ° C for 4 hours. After the reaction is completed, water should be added to precipitate yellow crystals. Filter with a Buchner funnel, wash with a small amount of ice methanol and then dry. The obtained solid is the Schiff base ligand. 1 HNMR (400MHz, CDCl3) δ13.8 (s, 1H), 9.50 (s, 1H), 8.24 (d, J = 6.0Hz, 1H), 7.1 4(d,J=6.0Hz,1H),7.10–7.00(m,3H),6.99–9.94(m,1H),6.74–6.51(m,2H). 13 C NMR (101MHz, CDCl3) δ165.0,162.5,157.5,148.7,137.7,133.7,133.5,122.0,120.4,118.9,117.4.

[0032] 2) Preparation of Schiff base aluminum compounds

[0033] Under anhydrous and oxygen-free conditions and nitrogen protection, 6.69 mmol of diisobutylaluminum hydride was slowly added dropwise to a 6.67 mmol toluene solution of the Schiff base ligand in a Schlenk reaction flask at low temperature. After stirring overnight at room temperature, the mixture was allowed to stand and filtered. The toluene was then concentrated and placed in a low-temperature refrigerator. The next day, a large amount of crystals was obtained, which is the Schiff base aluminum compound. The yield was 67%. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ8.00(dd,J=5.1,1.8Hz,1H),7.44(s,1H),7.22(dd,J=7.5,1.7Hz,1H),7.12(td,J=7.7,1.8H z,1H),6.90–6.76(m,2H),6.65–6.48(m,2H),4.39(s,2H),3.37(s,1H),0.94(p,J=10.8,9.0Hz,6H),-0.10(s,2H). 13 CNMR (101MHz, CDCl3) δ167.7,166.9,155.0,148.7,138.5,138.0,136.2,122.4,122.3,118.7,117.2,115.4,27.2,24.2,22.3,21.2.

[0034] Example 2: Synthesis of alkenyl borate esters from phenylacetylene and pinacol borane catalyzed by a Schiff base aluminum compound.

[0035] Under anhydrous and oxygen-free conditions and nitrogen atmosphere in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of phenylacetylene was added. After heating at 60°C for 10 hours, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl₃. The calculated H₄ yield was 99%. The product's NMR data were as follows: 1 H NMR(400MHz,Chloroform-d)δ7.57–7.45(m,2H),7.22–7.15(m,1H),7.04(td,J=7.7, 1.2Hz, 1H), 6.96 (ddd, J=10.6, 8.2, 1.2Hz, 1H), 6.17 (d, J=18.6Hz, 1H), 1.24 (s, 12H). 13 C NMR (101MHz, CDCl3) δ148.48,136.45,127.85,127.53,126.01,82.28,23.78.

[0036] Example 3: Synthesis of alkenyl borate esters from p-fluorophenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0037] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of p-fluorophenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.50–7.42(m,2H),7.35(d,J=18.4Hz,1H),7.02(t,J=8.6Hz,2H),6.07(d,J=18.4Hz,1H),1.31(s,12H). 13 C NMR (101MHz, CDCl3) δ163.36,160.89,147.14,132.70,127.73,127.64,114.64,114.43,82.37,23.78.

[0038] Example 4: Synthesis of alkenyl borate esters from p-methylphenylacetylene and pinacol borane catalyzed by a Schiff base aluminum compound.

[0039] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of p-methylphenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.39–7.20(m,4H),7.05(d,J=7.9Hz,3H),6.03(d,J=18.5Hz,1H),2.25(s,3H),1.22(s,12H). 13 CNMR (101MHz, CDCl3) δ149.52,138.97,134.84,129.32,127.05,83.29,24.84,21.35.

[0040] Example 5: Synthesis of alkenyl borate esters from p-methyloxyphenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0041] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of p-methoxyphenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.46–7.40(m,2H),7.35(d,J=18.4Hz,1H),6.86(d,J=8.8Hz,2H),6.01(d,J=18.4Hz,1H),3.81(s,3H),1.31(s,12H). 13 C NMR (101MHz, CDCl3) δ160.31,149.08,130.43,128.48,113.99,83.22,55.28,24.82.

[0042] Example 6: Synthesis of alkenyl borate esters from m-fluorophenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0043] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of m-fluorophenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.26(d,J=18.4Hz,1H),7.22–7.12(m,3H),7.09(d,J=10.0Hz,1H),6.89(t,J=7.6Hz,1H),6.08(d,J=18.4Hz,1H),1.22(s,12H). 13 C NMR (101MHz, CDCl3) δ163.28,160.84,147.04,147.02,138.89,138.82,129. 03,128.95,121.98,121.95,114.74,114.53,112.36,112.14,82.45,23.77.

[0044] Example 7: Synthesis of alkenyl borate esters from m-methylphenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0045] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of m-methylphenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR(400MHz, CDCl3)δ7.29(d,J=18.4Hz,1H),7.23–7.18(m,2H),7.16–7.09(m, 1H),7.01(d,J=7.4Hz,1H),6.07(d,J=18.4Hz,1H),2.25(s,3H),1.22(s,12H). 13 C NMR (101MHz, CDCl3) δ148.65,137.04,136.45,128.67,127.42,126.75,123.21,82.26,23.79,20.35.

[0046] Example 8: Synthesis of alkenyl borate esters from m-trifluoromethylphenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0047] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of m-trifluoromethylphenylacetylene was added. After heating at 60°C for 10 hours, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.62(d,J=2.1Hz,1H),7.55(d,J=7.7Hz,1H),7.43(d,J=7.7Hz,1H),7.38–7.27(m,2H),6.15(d,J=18.4Hz,1H),1.22(s,12H). 13 C NMR (101MHz, CDCl3) δ146.63,137.26,130.53,130.21,129.89,129.57,128. 98,128.96,128.05,124.39,124.27,122.71,121.69,118.98,82.53,23.75.

[0048] Example 9: Synthesis of alkenyl borate esters from m-o-fluorophenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0049] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of o-fluorophenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.56–7.41(m,2H),7.19(s,1H),7.04(td,J=7.7,1.2Hz, 1H), 6.96 (ddd, J=10.6, 8.2, 1.2Hz, 1H), 6.17 (d, J=18.6Hz, 1H), 1.24 (s, 12H). 13 C NMR (101MHz, CDCl3) δ160.95,158.45,140.32,140.28,129.18,129.10,126. 40,126.37,124.44,124.32,123.09,123.05,114.91,114.69,82.43,23.79.

[0050] Example 10: Synthesis of alkenyl borate esters from o-methylphenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0051] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of o-methylphenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.65(d,J=18.3Hz,1H),7.56(dd,J=6.6,2.5Hz,1H),7.22–7.11(m,3H),6.09(d,J=18.2Hz,1H),2.43(s,3H),1.32(s,12H). 13C NMR (101MHz, CDCl3) δ146.11,135.69,135.27,129.37,127.54,125.08,124.76,82.27,23.80,18.79.

[0052] Example 11: Synthesis of alkenyl borate esters from o-trifluoromethylphenylacetylene and pinacol borane catalyzed by Schiff base aluminum compounds.

[0053] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of o-trifluoromethylphenylacetylene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.71–7.61(m,2H),7.56(d,J=7.9Hz,1H),7.44(t,J=7.6Hz,1H),7.30(t,J=7.7Hz,1H),6.08(d,J=18.0Hz,1H),1.24(s,12H). 13 C NMR (101MHz, CDCl3) δ143.72,135.94,130.84,127.16,126.48,124.74,124.68,124.56,121.84,82.53,23.78.

[0054] Example 12: Synthesis of alkenyl borate esters from m-ethynylcyclohexene and pinacol borane catalyzed by a Schiff base aluminum compound.

[0055] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of 1-ethynylcyclohexene was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ7.02(d,J=18.2Hz,1H),5.96(d,J=2.3Hz,1H),5.43(d,J= 18.3Hz, 1H), 2.15 (d, J=4.6Hz, 4H), 1.62 (dd, J=29.4, 9.5Hz, 4H), 1.27 (s, 12H).13 C NMR (101MHz, CDCl3) δ152.22,136.15,133.24,82.00,25.16,23.75,22.74,21.40,21.33.

[0056] Example 12: Synthesis of alkenyl borate esters from m-1-heptyne and pinacol borane catalyzed by a Schiff base aluminum compound.

[0057] Under anhydrous and oxygen-free conditions and nitrogen protection in a glove box, 0.05 mmol of the catalyst was added to a 10 ml Schlenk reaction flask. 1.0 mmol of pinacol borane was then added and mixed thoroughly. Finally, 1.0 mmol of 1-heptyne was added. After heating at 60°C for 10 h, the reaction was terminated by exposing to air. The crude product was purified by column chromatography using petroleum ether / ethyl acetate as the eluent to obtain the product. The product was sampled and dissolved in CDCl3. The NMR data of the product are as follows: 1 H NMR (400MHz, CDCl3) δ6.73-6.66 (m, 1H), 5.51-5.46 (d,, J = 18.01Hz, 1H), 2.22-2. 17(q,2H),1.48-1.43(br,4H),1.31(s,12H),1.28-1.23(m,4H),0.95-0.92(s,3H) 13 C NMR (101MHz, CDCl3) δ154.59,82.77,35.73,31.64,28.83,28.11,24.64,22.50,13.96.

Claims

1. A Schiff base aluminum compound having the following structure.

2. A method for preparing the Schiff base aluminum compound according to claim 1, characterized in that: The steps include: (1) Under nitrogen protection, 2-aminopyridine, salicylaldehyde and hydrochloric acid were refluxed in anhydrous methanol solvent at a molar ratio of 1:1:0.001 for 4 hours. After the reaction, water was added to precipitate yellow crystals, which were filtered, washed with a small amount of ice methanol and then dried to obtain a solid Schiff base ligand; (2) Under anhydrous and oxygen-free conditions and under nitrogen protection, diisobutylaluminum chloride is slowly added dropwise to the toluene solution of the above-mentioned ligand in a Schlenk reaction flask at low temperature, with a molar ratio of 1:

1. The mixture is stirred at room temperature overnight, allowed to stand and filtered, and then the toluene is concentrated and placed in a low-temperature refrigerator to obtain a large amount of crystals the next day, which are Schiff base aluminum compounds.

3. Use of the Schiff base aluminum compound according to claim 1 in the hydroboration reaction of alkynes.

4. The use according to claim 3, characterized in that: The alkyne is selected from one of aromatic alkynes and aliphatic alkynes; and the borane is pinacol borane.

5. The use according to claim 4, characterized in that: The chemical structure of the aromatic alkyne is In the formula, R is hydrogen, halogen, methyl, or trifluoromethyl.

6. The use according to claim 4, characterized in that: The aliphatic alkyne is 1-ethynylcyclohexene or 1-heptyne.

7. The use according to claim 3, characterized in that: The molar ratio of Schiff base aluminum compound: alkyne: borane is 0.05:1:1, and the hydroboration reaction temperature is 60° C. and the reaction time is 10 h.

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