A method for the photochemical reduction-coupling of aryl alpha-keto esters to synthesize 2,3-diaryl tartaric esters

Abstract

This invention belongs to the field of catalytic synthesis technology for fine chemical products, and discloses a method for photochemical reductive coupling of aryl α-keto esters to synthesize 2,3-diaryl tartrate esters. The method includes the following steps: in an inert atmosphere, the substrate aryl α-keto ester, an electron-sacrificing reagent, a proton-sacrificing reagent, and an organic solvent are mixed, and a selective reductive coupling reaction is carried out under visible light irradiation. After the reaction, 2,3-diaryl tartrate esters are obtained by separation and purification. This invention achieves the reductive coupling of aryl α-keto esters through a hydrogen transfer strategy, avoiding the use of hazardous hydrogen gas, eliminating the formation of reduction products, providing mild reaction conditions, and achieving high reaction yields, thus showing great application potential.

Description

Technical Field

[0001] This invention relates to the field of catalytic synthesis technology for fine chemical products, specifically to a method for synthesizing 2,3-diaryl tartrate esters by photochemical reduction coupling of aryl α-keto esters. Background Technology

[0002] Tartaric acid and its derivatives are widely used in the pharmaceutical industry as antioxidants, anti-inflammatory agents, and antihypertensive agents, and in the food industry as acidifying agents. The core structure of these derivatives features two carbonyl groups, four hydroxyl groups, and two chiral centers. This unique arrangement endows them with multifunctional properties, including acting as proton donors / acceptors, hydrogen bond donors, and transition metal ligands. Therefore, tartaric acid and its derivatives are also highly valuable organic catalysts, chiral ligands, and chiral structural units in synthetic chemistry.

[0003] Traditional synthetic routes for the tartaric acid skeleton primarily rely on the catalytic oxidation of maleic acid or glucose using stoichiometric oxidants. Catalytic reductive coupling of α-keto esters via keto-keto radical coupling has emerged as a powerful and efficient strategy for synthesizing 2,3-disubstituted tartaric acid ester derivatives. Pioneering research has mainly utilized stoichiometric metal reducing agents, such as SmI₂, Mg, or TiCl₃, as single-electron donors, or reductive coupling under UV irradiation in the presence of a reducing agent. However, these methods suffer from significant drawbacks, including metal residues, harsh reaction conditions, and complex product mixtures.

[0004] In recent years, visible light-induced catalysis has attracted considerable attention due to its green and sustainable characteristics, and has become an important technique in organic synthesis. In the field of reductive carbonyl dimerization, chemists have developed proton-coupled electron transfer (PCET) strategies to overcome the high redox potentials of carbonyl compounds, achieving the conversion of alkane α-keto esters to tartaric acid derivatives. However, current methods have a very limited substrate applicability and cannot achieve photochemical reductive coupling of aryl α-keto esters. Since aryl α-keto esters can be directly excited by visible light and can form keto radicals in the presence of electron donors, we explored a method for the reductive coupling of aryl α-keto esters to 2,3-diaryl tartaric acid esters through keto radical dimerization in a photocatalyst-free system.

[0005] In summary, the study of reductive coupling reaction systems without photocatalysts is one of the important research contents in synthetic chemistry. Among them, the use of inexpensive electron and proton donors to complete the reductive coupling of aryl α-keto esters to obtain the corresponding 2,3-diaryl tartrate esters is also an urgent problem to be solved. Summary of the Invention

[0006] To address the technical problem that existing methods cannot achieve photo-driven reductive coupling of aryl α-keto esters, this invention provides a method for photochemical reductive coupling of aryl α-keto esters to synthesize 2,3-diaryl tartaric acid esters. This method can more gently and efficiently reduce aryl α-keto esters to synthesize 2,3-diaryl tartaric acid esters.

[0007] To achieve the above objectives, the present invention provides a method for synthesizing 2,3-diaryl tartrate by photochemical reduction coupling of aryl α-keto esters, comprising the following steps: in an inert atmosphere, mixing the substrate aryl α-keto ester, a proton sacrificial reagent, an electron sacrificial reagent and an organic solvent, and carrying out a selective reduction coupling reaction under visible light irradiation; after the reaction is completed, 2,3-diaryl tartrate is obtained by separation and purification.

[0008] Furthermore, the general structural formula of the aryl α-keto ester is as follows: Among them, R 1 Selected from any one of alkyl, methoxy, methylthio, halogen substituents (fluorine, chlorine, bromine, iodine), ester, cyano, or trifluoromethoxy; R 2 It can be methyl or ethyl.

[0009] Furthermore, both the proton sacrificial reagent and the electron sacrificial reagent are ascorbic acid.

[0010] Furthermore, the amount of ascorbic acid used is 1-3 times the molar amount of aryl α-keto ester, preferably 2 times.

[0011] Furthermore, the organic solvent is ultra-dry methanol (water content ≤50ppm) or tetrahydrofuran. Even further, 5-10L of organic solvent is added for every 1mol of the substrate aryl α-keto ester.

[0012] Furthermore, the wavelength of the visible light is 440nm-445nm, and the light intensity is 50mW / cm²-100mW / cm².

[0013] Furthermore, the temperature of the reduction coupling reaction is 25℃-30℃, and the reaction time is 14h-17h.

[0014] Furthermore, the inert atmosphere is nitrogen or argon, preferably nitrogen.

[0015] Furthermore, the yield of the 2,3-diaryl tartrate ester is 84%-95%.

[0016] Furthermore, the reaction does not require the addition of a photocatalyst.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: (1) No photocatalyst is required, and environmentally friendly and sustainable visible light is used as the energy source; (2) The reaction conditions are mild, the electron sacrificial reagent is ascorbic acid, which is cheap and readily available, the reaction operation is simple, and it is suitable for large-scale production; (3) In addition, the cheap ascorbic acid is used as a proton sacrificial reagent (hydrogen source), avoiding the special requirements for equipment and safety when hydrogen is used as the hydrogen source.

[0018] In summary, this invention has the advantages of inexpensive and readily available reagents, mild reaction conditions, simple process operation, and high reaction yield, and is a promising method for the synthesis of 2,3-diaryl tartrate esters. Attached Figure Description

[0019] Figure 1 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 1; Figure 2 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 1; Figure 3 The hydrogen spectrum of meso-2,3-diaryl tartrate obtained in Example 1; Figure 4 The carbon spectrum of meso-2,3-diaryl tartrate obtained in Example 1; Figure 5 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 2; Figure 6 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 2; Figure 7 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 3; Figure 8 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 3; Figure 9 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 4; Figure 10 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 4; Figure 11 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 5; Figure 12 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 5; Figure 13 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 6; Figure 14 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 6; Figure 15 The fluorine spectrum of dl-2,3-diaryl tartrate obtained in Example 6; Figure 16 The hydrogen spectrum of dl-2,3-diaryl tartrate obtained in Example 7; Figure 17 The carbon spectrum of dl-2,3-diaryl tartrate obtained in Example 7; Figure 18 The fluorine spectrum of dl-2,3-diaryl tartrate obtained in Example 7; Figure 19 The reaction equation for the photochemical reduction coupling of aryl α-keto esters to synthesize 2,3-diaryl tartrate esters is shown in a preferred embodiment of the present invention. Detailed Implementation

[0020] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0021] According to one embodiment of the present invention, a technical solution for the photochemical reduction coupling of aryl α-keto esters to synthesize 2,3-diaryl tartrate esters is provided as follows: In an inert atmosphere, an electron-sacrificing reagent and an aryl α-keto ester are dissolved in an organic solvent, and a reductive coupling reaction of the aryl α-keto ester is carried out under blue light irradiation to generate the 2,3-diaryl tartrate product.

[0022] In some embodiments, the electron sacrificial agent is ascorbic acid, and the solvent is ultra-dry methanol or tetrahydrofuran.

[0023] In some embodiments, the amount of the electron sacrificial reagent is 1-3 times the molar amount of the aryl α-keto ester, preferably 2 times; the reaction time is 14-17 hours.

[0024] In some embodiments, the general structural formula of the aryl α-keto ester is as follows: R 1 Selected from any one of the following groups: alkyl, methoxy, methylthio, halogen (fluorine, chlorine, bromine, iodine), ester, cyano, trifluoromethoxy, R 2 It can be methyl or ethyl.

[0025] In some embodiments, the reaction is carried out in an inert atmosphere, and various inert gas atmospheres are applicable, not limited to a nitrogen atmosphere.

[0026] In some embodiments, the reduction reaction is performed using a sealable glass or quartz reactor.

[0027] The embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the invention. For those skilled in the art, other equivalent embodiments based on the present invention can be obtained without creative effort, and all such embodiments should be considered to fall within the protection scope of the present invention.

[0028] Unless otherwise specified, all raw materials used in the following examples are publicly available in the prior art, such as those that can be directly purchased or prepared according to publicly available methods. Methanol in the examples is a commercially available ultra-dry solvent; other reagents and solvents are commercially available products without further purification. All reactions were carried out under a nitrogen atmosphere. Nuclear magnetic resonance (NMR) spectra were measured using a Bruker Avance-400 spectrometer in the specified solvents: chemical shifts are reported in ppm. 1 The H spectrum was defined with the TMS resonance peak at 0.00 ppm or the CHCl3 resonance peak in CDCl3 at 7.26 ppm as a reference. 13 The C-ray spectroscopy spectrum was referenced with the CDCl3 resonance peak set at 77.00 ppm. Coupling constants were reported in Hertz (Hz), and peak splitting modes were labeled as: s (singleton), d (doublet), t (triplet), q (quartet), and m (multiplex). The diastereomer ratio (dl / meso value) was calculated based on the weight of the separated products and the coarse NMR spectrum; some products were separated into meso-type products.

[0029] This invention provides a photochemical system for the photoinduced reduction coupling of aryl α-keto esters to synthesize 2,3-diaryl tartrate esters; in the system, ascorbic acid is used as an electron sacrificial reagent and as a proton sacrificial reagent, and the efficient reduction coupling of aryl α-keto esters is 2,3-diaryl tartrate esters.

[0030] This method can be performed as follows: (1) First add solid reagents into the glass tube, such as ascorbic acid, solid aryl α-keto ester raw materials; (2) After protecting the atmosphere inside the tube with nitrogen, add the solvent methanol or THF under nitrogen conditions and seal it. (3) Irradiate with blue light with a wavelength of 440-445nm for 14-17 hours; (4) After the reaction is complete, the solvent is removed by vacuum distillation, and the product is obtained by column chromatography.

[0031] In the following embodiments: Total yield = weight of the purified product (mg) ÷ molecular weight of the product × 0.2 mmol.

[0032] Example 1: Reductive coupling of methyl benzoylformate Ascorbic acid (70.4 mg, 2.0 equiv.) and methyl benzoate (32.8 mg, 1.0 equiv.) were weighed separately and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. 1.5 mL of methanol was added using a syringe under nitrogen atmosphere. The reaction tube was sealed and irradiated with blue light (wavelength 440-445 nm) for 16 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 2,3-diaryl tartrate product 2, totaling 57.4 mg, with an overall yield of 87% (dl / meso = 3 / 1). The structural formula of product 2 is shown below: like Figure 1 The hydrogen spectrum of product dl-2 is shown below: 1 H NMR (400 MHz, Chloroform- d δ 7.24-7.22 (m, 2H), 7.17-7.13 (m, 4H), 7.09-7.07 (m, 4H), 5.11 (s, 2H), 3.85 (s, 6H). The chemical shifts (unit: ppm) 7.24-7.22 (m, 2H), 7.17-7.13 (m, 4H), and 7.09-7.07 (m, 4H) represent hydrogens in the benzene ring region of the structure, 5.11 (s, 2H) represents hydroxyl hydrogens, and 3.85 (s, 6H) represents methoxy hydrogens.

[0033] like Figure 2 The carbon spectrum of product dl-2 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 176.13(2C), 134.56(2C), 128.19(2C), 127.06(4C), 127.02(4C), 82.01(2C), 53.41(2C). Among them, the chemical shift (unit: ppm) is 176.13(2C) for the carbonyl carbon in the structure, 134.56(2C), 128.19(2C), 127.06(4C), 127.02(4C) for the carbon in the benzene ring, 82.01(2C) for the carbon attached to the hydroxyl group, and 53.41(2C) for the carbon with the methoxy group.

[0034] like Figure 3The hydrogen spectrum of product meso-2 is shown below: 1 ¹H NMR (400 MHz, Chloroform-d) δ 7.29–7.25 (m, 4H), 7.24–7.20 (m, 2H), 7.19–7.14 (m, 4H), 4.21 (s, 2H), 3.73 (s, 6H). Chemical shifts (in ppm): 7.29–7.25 (m, 4H), 7.24–7.20 (m, 2H), and 7.19–7.14 (m, 4H) represent hydrogens in the benzene ring region of the structure; 4.21 (s, 2H) represents a hydroxyl hydrogen; and 3.73 (s, 6H) represents a methoxy hydrogen.

[0035] like Figure 4 The carbon spectrum of the product meso-2 is shown below: 13 C NMR (101 MHz, Chloroform-d) δ 172.53 (2C), 135.65 (2C), 128.42 (2C), 127.93 (4C), 127.06 (4C), 83.10 (2C), 53.16 (2C). Among them, the chemical shift (unit: ppm) is 172.53 (2C) for the carbonyl carbon in the structure, 135.65 (2C), 128.42 (2C), 127.93 (4C), 127.06 (4C) for the carbon in the benzene ring, 83.10 (2C) for the carbon attached to the hydroxyl group, and 53.16 (2C) for the carbon with the methoxy group.

[0036] Example 2: Reductive coupling of ethyl 4-methoxybenzoylcarbamate Ascorbic acid (70.4 mg, 2.0 equiv.) and ethyl 4-methoxybenzoylformate (41.6 mg, 1.0 equiv.) were weighed separately and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. Under nitrogen conditions, 1.5 mL of methanol was injected using a syringe, and the reaction tube was sealed. The tube was then irradiated with blue light (wavelength 440-445 nm) for 16 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 75.2 mg of 2,3-diaryl tartrate product 3. The overall yield was 90% (dl / meso = 1.3 / 1). The structural formula of product 3 is shown below: like Figure 5 The hydrogen spectrum of product 3 is shown below: 1 H NMR (400 MHz, Chloroform- d ) δ 7.02 (d, J=8.9 Hz, 4H), 6.69 (d, J = 8.9 Hz, 4H), 4.98 (s, 2H), 4.35-4.26 (m, 4H), 3.76(s, 6H), 1.29 (t, J = 7.1 Hz, 6H). The chemical shift (unit: ppm) is 7.02 (d, J = 8.9 Hz, 4H), 6.69 (d, J = 8.9 Hz, 4H) is the hydrogen in the benzene ring region of the structure, 4.98 (s, 2H) is the hydroxyl hydrogen, 4.35-4.26 (m, 4H) is the methylene oxy group peak, 3.76 (s, 6H) is the methoxy hydrogen, and 1.29 (t, J = 7.1 Hz, 6H) is the methyl hydrogen.

[0037] like Figure 6 The carbon spectrum of product 3 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 175.69 (2C),159.36 (2C), 128.56 (4C), 127.13 (2C), 112.31 (4C), 81.84 (2C), 62.59 (2C), 55.13 (2C), 13.92 (2C). Among them, the chemical shift (unit: ppm) is 175.69 (2C) for the carbonyl carbon in the structure, 159.36 (2C), 128.56 (4C), 127.13 (2C), 112.31 (4C) for the carbon in the benzene ring region, 81.84 (2C) for the carbon attached to the hydroxyl group, 62.59 (2C) for the methyleneoxy peak, 55.13 (2C) for the methoxy carbon, and 13.92 (2C) for the methyl carbon.

[0038] Example 3: Reductive coupling of methyl 4-methylthiobenzoylcarbamate Ascorbic acid (70.4 mg, 2.0 equiv.) and methyl 4-methylthiobenzoylformate (42.0 mg, 1.0 equiv.) were weighed separately and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. Under nitrogen conditions, 1.5 mL of methanol was injected using a syringe, and the reaction tube was sealed. The tube was then irradiated with blue light (wavelength 440-445 nm) for 16 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 77.6 mg of 2,3-diaryl tartrate product 4. The overall yield was 92% (dl / meso = 2 / 1). The structural formula of product 4 is shown below: like Figure 7 The hydrogen spectrum of product 4 is shown below: 1 H NMR (400 MHz, Chloroform- d δ 7.03 (s, 8H), 5.00 (s, 2H), 3.84 (s, 6H), 2.43 (s, 6H). Wherein the chemical shifts (unit: ppm) 7.03 (s, 8H) are hydrogens in the benzene ring region of the structure, 5.00 (s, 2H) are hydroxyl hydrogens, 3.84 (s, 6H) are methoxy hydrogens, and 2.43 (s, 6H) are thiomethyl hydrogens.

[0039] like Figure 8 The carbon spectrum of product 4 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 175.83 (2C),138.80 (2C), 131.32 (2C), 127.56 (4C), 124.80 (4C), 81.84 (2C), 53.45 (2C),15.40 (2C). Among them, the chemical shift (unit: ppm) is 175.83 (2C) for carbonyl carbon in the structure, 138.80 (2C), 131.32 (2C), 127.56 (4C), 124.80 (4C) for carbon in the benzene ring, 81.84 (2C) for carbon attached to hydroxyl group, 53.45 (2C) for carbon with methoxy group, and 15.40 (2C) for carbon with thiomethyl group.

[0040] Example 4: Reductive Coupling of Methyl 4-Iodobenzoylcarbamate Ascorbic acid (70.4 mg, 2.0 equiv.) and methyl 4-iodobenzoylformate (57.9 mg, 1.0 equiv.) were weighed separately and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. Under nitrogen conditions, 1.5 mL of methanol was injected using a syringe, and the reaction tube was sealed. The tube was then irradiated with blue light (wavelength 440-445 nm) for 16 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 104.6 mg of 2,3-diaryl tartrate product 5. The overall yield was 90% (dl / meso = 1.4 / 1). The structural formula of product 5 is shown below: like Figure 9 The hydrogen spectrum of product 5 is shown below: 1 H NMR (400 MHz, Chloroform- d ) δ 7.50 (d,J =8.6 Hz, 4H), 6.86 (d, J = 8.6 Hz, 4H), 4.97 (s, 2H), 3.84 (s, 6H). The chemical shift (unit: ppm) is 7.50 (d, J = 8.6 Hz, 4H), 6.86 (d, J = 8.6 Hz, 4H) is the hydrogen in the benzene ring region of the structure, 4.97 (s, 2H) is the hydroxyl hydrogen, and 3.84 (s, 6H) is the methoxy hydrogen.

[0041] like Figure 10 The carbon spectrum of product 5 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 175.21(2C), 136.33 (4C), 134.30 (2C), 129.04 (4C), 94.80 (2C), 81.60 (2C), 53.65(2C). Among them, the chemical shift (unit: ppm) is 175.21 (2C) for the carbonyl carbon in the structure, 136.33 (4C), 134.30 (2C), 129.04 (4C) for the carbon in the benzene ring region, 94.80 (2C) for the carbon attached to iodine, 81.60 (2C) for the carbon attached to the hydroxyl group, and 53.65 (2C) for the carbon attached to the methoxy group.

[0042] Example 5: Reductive coupling of ethyl 4-cyanobenzoylcarbamate Ascorbic acid (70.4 mg, 2.0 equiv.) and ethyl 4-cyanobenzoylcarbamate (40.6 mg, 1.0 equiv.) were weighed and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. Under nitrogen conditions, 1.5 mL of methanol was injected using a syringe, and the reaction tube was sealed. The tube was then irradiated with blue light (wavelength 440-445 nm) for 16 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 74.2 mg of 2,3-diaryl tartrate product 6. The overall yield was 91% (dl / meso = 1.4 / 1). The structural formula of product 6 is shown below: like Figure 11 The hydrogen spectrum of product 6 is shown below: 1 H NMR (400 MHz, Chloroform- d ) δ 7.45 (d, J =8.5 Hz, 4H), 7.29 (d, J= 8.5 Hz, 4H), 5.08 (s, 2H), 4.38-4.30 (m, 4H), 1.30(t, J = 7.1 Hz, 6H). The chemical shift (unit: ppm) is 7.45 (d, J = 8.5 Hz, 4H), 7.29 (d, J =8.5 Hz, 4H) represents the hydrogen in the benzene ring region of the structure, 5.08 (s, 2H) represents the hydroxyl hydrogen, 4.38-4.30 (m, 4H) represents the methyleneoxy peak, and 1.30 (t, J = 7.1 Hz, 6H) is methyl hydrogen.

[0043] like Figure 12 The carbon spectrum of product 6 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 173.61(2C), 139.72(2C), 130.94(4C), 127.92(4C), 118.35(2C), 112.43(2C), 81.33(2C), 63.53(2C), 13.85(2C). Among them, the chemical shift (unit: ppm) is 173.61(2C) for the carbonyl carbon in the structure, 139.72(2C), 130.94(4C), and 127.92(4C) for the carbon in the benzene ring region, 118.35(2C) for the cyano carbon, 112.43(2C) for the carbon attached to the cyano group, 81.33(2C) for the carbon attached to the hydroxyl group, 63.53(2C) for the methyleneoxy peak, and 13.85(2C) for the methyl carbon.

[0044] Example 6: Reductive Coupling of Methyl 4-Cyanobenzoylcarbamate Ascorbic acid (70.4 mg, 2.0 equiv.) and methyl 4-cyanobenzoylformate (49.6 mg, 1.0 equiv.) were weighed separately and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. Under nitrogen conditions, 1.5 mL of methanol was injected using a syringe, and the reaction tube was sealed. The tube was then irradiated with blue light (wavelength 440-445 nm) for 16 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 85.7 mg of 2,3-diaryl tartrate product 7. The overall yield was 86% (dl / meso = 1.7 / 1). The structural formula of product 7 is shown below: like Figure 13 The hydrogen spectrum of product 7 is shown below: 1H NMR (400 MHz, Chloroform- d ) δ 7.13 (d, J =8.9 Hz, 4H), 6.99 (d, J = 8.9 Hz, 4H), 5.08 (s, 2H), 3.87 (s, 6H). The chemical shift (unit: ppm) is 7.13 (d, J = 8.9 Hz, 4H), 6.99 (d, J = 8.9 Hz, 4H) is the hydrogen in the benzene ring region of the structure, 5.08 (s, 2H) is the hydroxyl hydrogen, and 3.87 (s, 6H) is the methyl hydrogen.

[0045] like Figure 14 The carbon spectrum of product 7 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 175.20(2C), 149.29 (2C), 133.05 (2C), 128.63 (4C), 121.62 (2C), 119.40 (4C), 81.45(2C), 53.70 (2C). Among them, the chemical shift (unit: ppm) is the carbonyl carbon in the structure at 175.20 (2C), 149.29 (2C), 133.05 (2C), 128.63 (4C), 121.62 (2C), 119.40 (4C) is the carbon in the benzene ring and the trifluoromethoxy carbon, 81.45 (2C) is the carbon attached to the hydroxyl group, and 53.70 (2C) is the methoxy carbon.

[0046] like Figure 15 The fluorine spectrum of product 7 is shown below: 19 F NMR (376 MHz, ) δ -57.93 (s, 6F). Example 7: Reductive coupling of ethyl 3-fluoro-4-methoxybenzoylcarbamate Ascorbic acid (70.4 mg, 2.0 equiv.) and ethyl 3-fluoro-4-methoxybenzoylcarbamate (48.4 mg, 1.0 equiv.) were weighed separately and added to a 10 mL capped glass tube. The air in the reaction tube was then replaced with nitrogen. Under nitrogen conditions, 1.5 mL of methanol was injected using a syringe, and the reaction tube was sealed. The tube was then irradiated with blue light (wavelength 440-445 nm) for 17 h. After the reaction was stopped, the reaction solution was evaporated to dryness and separated by column chromatography to obtain 25.4 mg of 2,3-diaryl tartrate product 8, with an overall yield of 56%. The structural formula of product 8 is shown below: like Figure 16 The proton NMR spectrum of product 8 is shown below: 1 H NMR (400 MHz, Chloroform- d ) δ 6.97-6.86(m, 4H), 6.75 (t, J = 8.6 Hz, 2H), 4.96 (s, 2H), 4.31 (qd, J = 7.1, 2.0 Hz, 4H),3.84 (s, 6H), 1.29 (t, J = 7.1 Hz, 6H). Chemical shifts (unit: ppm) are 6.97-6.86 (m, 4H), 6.75 (t, J = 8.6 Hz, 2H) represents the hydrogen in the benzene ring region of the structure, 4.96 (s, 2H) represents the hydroxyl hydrogen, and 4.31 (qd, J =7.1, 2.0 Hz, 4H) is methylene hydrogen, 3.84 (s, 6H) is methoxy hydrogen, 1.29 (t, J = 7.1 Hz, 6H) is methyl hydrogen.

[0047] like Figure 17 The carbon spectrum of product 8 is shown below: 13 C NMR (101 MHz, Chloroform- d ) δ 174.68(2C), 151.12 (d, J = 244.4 Hz, 2C), 147.43 (d, J = 10.1 Hz, 2C), 127.89 (d, J = 7.1Hz, 2C), 123.23 (d, J = 4.1 Hz, 2C), 115.54 (d, J = 21.2 Hz, 2C), 111.60 (d, J =2.1 Hz, 2C), 81.25 (d, J = 2.1 Hz, 2C), 62.91 (2C), 56.06 (2C), 13.86 (2C). The chemical shift (unit: ppm) at 174.68 (2C) represents the carbonyl carbon in the structure, and at 151.12 (d, J = 244.4 Hz, 2C), 147.43 (d, J= 10.1 Hz, 2C), 127.89 (d, J = 7.1 Hz, 2C), 123.23 (d, J = 4.1 Hz, 2C), 115.54 (d, J = 21.2 Hz, 2C), 111.60 (d, J = 2.1 Hz, 2C) is carbon in the benzene ring region, 81.25 (d, J = 2.1 Hz, 2C) is the carbon linked to the hydroxyl group, 62.91 (2C) is the methyleneoxy peak, 56.06 (2C) is the methoxy carbon, and 13.86 (2C) is the methyl carbon.

[0048] like Figure 18 The fluorine spectrum of product 8 is shown below: 19 F NMR (376 MHz, Chloroform- d ) δ -136.19 (s,2F). The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A method for synthesizing 2,3-diaryl tartrate esters by photochemical reduction coupling of aryl α-keto esters, characterized in that, Includes the following steps: In an inert atmosphere, the substrate aryl α-keto ester, electron sacrificial reagent, proton sacrificial reagent and organic solvent are mixed and subjected to selective reductive coupling reaction under visible light irradiation. After the reaction is completed, 2,3-diaryl tartrate is obtained by separation and purification.

2. The method according to claim 1, characterized in that, The general structural formula of the aryl α-keto ester is shown below: Among them, R 1 Selected from any one of alkyl, methoxy, methylthio, halogen substituents, ester, cyano, or trifluoromethoxy; R 2 It can be methyl or ethyl.

3. The method according to claim 1, characterized in that, Both the electron sacrificial reagent and the proton sacrificial reagent are ascorbic acid.

4. The method according to claim 3, characterized in that, The amount of ascorbic acid used is 1-3 times the molar amount of aryl α-keto ester.

5. The method according to claim 1, characterized in that, The organic solvent is ultra-dry methanol or tetrahydrofuran.

6. The method according to claim 1, characterized in that, The wavelength of the visible light is 440nm-445nm, and the light intensity is 50mW / cm²-100mW / cm².

7. The method according to claim 1, characterized in that, The reductive coupling reaction is carried out at a temperature of 25℃-30℃ for 14h-17h.

8. The method according to claim 1, characterized in that, The inert atmosphere is nitrogen or argon.

9. The method according to claim 1, characterized in that, The yield of the 2,3-diaryl tartrate ester was 84%-95%.

10. The method according to claim 1, characterized in that, The reaction does not require the addition of a photocatalyst.

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