A method for preparing a benzamide and its derivatives

Abstract

The present invention belongs to the technical field of organic synthesis, and provides a method for preparing benzamide and its derivatives, comprising the following steps: under photochemical catalysis, reacting 3-phenyl-1,4,2-dioxazol-5-one or its derivatives with pinacol borane to obtain benzamide and its derivatives. In the present invention, aryl dioxazolone is photochemically activated to remove CO2 to form a free radical, and a metal nitrene is constructed with the free radical through Fe(III) catalysis, and directly and selectively combines with the proton in pinacol borane to form an N-H bond, thereby obtaining benzamide or its derivatives. The raw materials are cheap and easily available, the synthesis is simple, the production cost can be effectively reduced, the yield and chemical selectivity can be improved, and it can be conveniently applied to the preparation of benzamide and its derivatives, having potential industrial application value.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic synthesis, and particularly relates to a method for preparing benzamide and its derivatives. Background Art

[0002] Benzamide and its derivatives have various applications in industry, mainly including the following aspects: 1. Pesticide raw materials: A variety of pesticide raw materials such as insecticides and herbicides can be derived through chemical synthesis. 2. Pharmaceutical intermediates: It can be used as a pharmaceutical intermediate for the production of various drugs, such as antibiotics, analgesics, and tumor drugs. 3. Important chemical intermediates. It can be used as a multi-purpose chemical intermediate to produce important chemical raw materials such as carboxylic acids and acyl chlorides, and can also be converted to synthesize natural heterocyclic compounds such as pyridine, imidazole, and pyridazine. 4. Important metal ligands, which are ligands of some important transition metals and are widely used in transition metal catalysts, photochemical catalyst ligands, etc. In short, benzamide has wide application value in industry and can meet the different needs of multiple industries.

[0003] Due to the various uses of such compounds, the research on the synthesis of benzamide and its derivatives has become a hot topic. Especially for the establishment of a simple and efficient method for synthesizing benzamide and its derivatives based on the structure of dioxazolone, the currently reported synthesis methods of benzamide and its derivatives mainly include the following several:

[0004] Using 1-phenylethane-1,2-diol as a raw material, under the catalysis of manganese oxide, using oxygen and ammonia as reaction gases, benzamide and its derivatives can be efficiently synthesized in a 1,4-dioxane solvent; this transformation uses inexpensive manganese oxide as an oxidant, with good selectivity, high conversion rate, and strong applicability. (Chem Volume 8, Issue 7, 14 July 2022, Pages 1906 - 1927)

[0005]

[0006] Using styrene as a raw material, under the catalysis of manganese oxide, using oxygen and ammonia as reaction gases, benzamide and its derivatives can be efficiently synthesized in tert-amyl alcohol solvent; this transformation uses inexpensive manganese oxide as an oxidant, with good selectivity, high conversion rate, and strong applicability. (JACSAu 2023, 3, 476 - 487)

[0007]

[0008] Using relatively inexpensive methyl benzoate as the raw material, sodium amide borane as the nitrogen source, and tetrahydrofuran as the solvent, the sodium benzoamide borane intermediate can be formed in a very short time at room temperature. After hydrolysis, benzoamide can be obtained. This method has strong substrate applicability and can react with a variety of substituted aromatic carboxylic acid esters. (Nature Communications volume 12, Article number: 5964 (2021));

[0009]

[0010] Using phenylacetic acid as the raw material, 1,2-dichloroethane as the solvent, and tert-butyl nitrite as the catalyst in 1 equiv., reacting with N-hydroxysuccinimide for two hours to obtain the intermediate active ester. Using ammonia as the nucleophile and reacting with this intermediate at room temperature for two hours, various benzamide derivatives can be synthesized. This method uses ammonia and inorganic acid esters, and can be directly obtained or purchased from some sections in industrial production. (Organic Letters 2023 25(19), 3402 - 3406)

[0011]

[0012] Using bromobenzene as the raw material and CuCN, with triethylamine as the base, reacting under different conditions. Reacting with 1.8 equiv. of CuCN and 1.6 equiv. of triethylamine in N-methylpyrrolidone and water with a volume ratio of 10:1 as the solvent at 170 °C for 18 - 28 h. Benzoamide was obtained. The reaction conditions are mild and the substrate range is wide. (Synlett 2023; 34(17): 1991 - 1996)

[0013]

[0014] Although such reactions can simply and efficiently synthesize benzamide and its derivatives with a wide range of substrate applicability, there are still several disadvantages: using strong alkaline substances causes environmental pollution to a certain extent; using strong oxidizing and reducing agents increases the danger of the reaction to a certain extent; and some use highly toxic raw materials or catalysts, which limits the application of the reaction. Summary of the Invention

[0015] The purpose of the embodiments of the present invention is to provide a method for preparing benzamide and its derivatives, aiming to solve the problems raised in the above background technology.

[0016] The embodiments of the present invention are implemented as follows. A preparation method of benzamide and its derivatives includes the following steps: In the presence of a solvent, under photocatalytic conditions with a wavelength range of 400 - 480 nm, using a ferric salt as a catalyst, reacting 3-phenyl-1,4,2-dioxazol-5-one with pinacol borane to obtain benzamide and its derivatives. The reaction formula is as follows:

[0017]

[0018] Preferably, in the above preparation method, the catalyst is one or more of ferric chloride, ferric bromide, ferric fluoride, iron(III) trifluoromethanesulfonate, and ferric sulfate.

[0019] Preferably, in the above preparation method, the photocatalytic light source selected for photocatalysis is blue light with an illumination intensity range of 5 - 18 W.

[0020] Preferably, in the above preparation method, the R1 group in benzamide and its derivatives is selected from hydrogen, halogen, substituted or unsubstituted C 1～10 alkyl, substituted or unsubstituted aryl, substituted or unsubstituted C 1～10 alkoxy, substituted or unsubstituted amino, carboxyl, ester group, acyl group, cyano group, nitro group, hydroxyl group, azide group.

[0021] Preferably, in the above preparation method, the molar ratio of 3-phenyl-1,4,2-dioxazol-5-one and its derivatives to pinacol borane is 1:2.

[0022] Preferably, in the above preparation method, the solvent is one or more of water, methanol, ethanol, acetonitrile, benzene, toluene, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, N,N-dimethylformamide, acetone, 1,2-dichloroethane, and dichloromethane.

[0023] Preferably, in the above preparation method, the reaction is carried out in air or an inert atmosphere, and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0024] Preferably, after the above preparation method is completed, the reaction solution is extracted with dichloromethane, washed with water multiple times using the organic phase and dried with anhydrous sodium sulfate. Finally, the organic phase is concentrated to obtain benzamide and its derivatives.

[0025] Preferably, the concentration is carried out by one of atmospheric distillation, vacuum distillation, and rotary evaporation.

[0026] Preferably, post-treatment can also be carried out by column chromatography purification. The column chromatography uses silica gel with 200 - 300 mesh as the separation resin, and the eluent is selected from at least one of petroleum ether, n-hexane, dichloromethane, water, acetonitrile, methanol, and ethyl acetate.

[0027] In the above method, the structural formula of benzamide and its derivatives is as follows:

[0028]

[0029] A method for preparing benzamide and its derivatives provided by an embodiment of the present invention reacts 3-phenyl-1,4,2-dioxazol-5-one or its derivative with pinacol borane (HBpin) under photochemical catalysis to obtain benzamide and its derivatives. In the present invention, aryl dioxazolone is photochemically activated to remove CO2 to form a free radical, and a metal nitrene is constructed with the free radical through Fe(III) catalysis, and directly and selectively combines with the proton in pinacol borane (HBpin) to form an N-H bond, thereby obtaining benzamide or its derivative. The raw materials are cheap and easily available, the synthesis is simple, the production cost can be effectively reduced, the yield and chemical selectivity can be improved, and it can be conveniently applied to the preparation of benzamide and its derivatives, having potential industrial application value. Description of the Drawings

[0030] Figure 1 1H NMR spectrum of compound 3a provided in Example 1 of the present invention; 1 H NMR spectrum;

[0031] Figure 2 13C NMR spectrum of compound 3a prepared in Example 1 of the present invention. 13 C NMR spectrum. Detailed Embodiments

[0032] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0033] The following describes the specific implementation of the present invention in detail with reference to specific embodiments.

[0034] A method for preparing benzamide and its derivatives, the steps are as follows:

[0035] In the presence of a solvent, under photochemical catalysis in a wavelength range of 400-480 nm, using a ferric salt as a catalyst, reacting 3-phenyl-1,4,2-dioxazol-5-one and its derivative with pinacol borane to obtain benzamide and its derivatives, and the reaction formula is as follows:

[0036]

[0037] Among them, the R1 group in benzamide and its derivatives is selected from hydrogen, halogen, substituted or unsubstituted C 1～10 alkyl, substituted or unsubstituted aryl, substituted or unsubstituted C1～10 One of an alkoxy group, a substituted or unsubstituted amino group, a carboxyl group, an ester group, an acyl group, a cyano group, a nitro group, a hydroxyl group, and an azide group.

[0038] According to the present invention, the catalyst is one or more of iron chloride, iron bromide, iron fluoride, iron trifluoromethanesulfonate, and iron sulfate. It should be understood that in the reaction of the present invention, the common point of the above catalysts is that they are all trivalent iron salt catalysts. In the present invention, aryl dioxazolone is photochemically activated to remove CO2 to form radicals, and metal nitrenes are constructed with radicals through Fe(III) catalysis, and directly and selectively combine with protons in pinacol borane (HBpin) to form N-H bonds, thereby obtaining benzamide or its derivatives. Therefore, as long as the types of the above catalysts are selected, the above reaction of the present application can be achieved. Although only the embodiments of individual catalyst types are given in the specific embodiments of the present invention, those skilled in the art should understand that the embodiments are only used to explain the preferred implementation schemes given by the present invention and are not used to limit the present invention. Under the inspiration given by the embodiments, those skilled in the art can also obtain the present invention according to other catalysts given by the present invention.

[0039] According to the present invention, the light intensity range of the light source selected for photochemical catalysis is 5 - 18 W.

[0040] According to the present invention, the molar ratio of 3-phenyl-1,4,2-dioxazol-5-one and its derivatives to pinacol borane is 1:2. It should be understood that in the reaction of the present invention, the molar ratio of 3-phenyl-1,4,2-dioxazol-5-one and its derivatives to pinacol borane being 1:2 only refers to the theoretical molar ratio of 3-phenyl-1,4,2-dioxazol-5-one and its derivatives to pinacol borane required in the reaction of the present invention, and does not mean that the feeding amounts during the reaction operation must be in the molar ratio of 3-phenyl-1,4,2-dioxazol-5-one and its derivatives to pinacol borane of 1:2.

[0041] According to the present invention, the solvent is one or more of water, methanol, ethanol, acetonitrile, benzene, toluene, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, N,N-dimethylformamide, acetone, 1,2-dichloroethane, and dichloromethane. It should be understood that in the reaction of the present invention, the above solvents are only used to dissolve 3-phenyl-1,4,2-dioxazol-5-one and its derivatives and pinacol borane, and the solvents themselves do not participate in the reaction. Therefore, as long as a solvent that can dissolve 3-phenyl-1,4,2-dioxazol-5-one and its derivatives and pinacol borane is selected, the above reaction of the present application can be achieved. Although only the example using 1,2-dichloroethane as the solvent is given in the following specific examples of the present invention, those skilled in the art should understand that the examples are only used to explain the preferred embodiments given by the present invention and are not used to limit the present invention. Under the inspiration of the examples, those skilled in the art can also use other solvents given by the present invention to obtain the present invention.

[0042] After the reaction of the present invention is completed, the reaction solution is extracted with dichloromethane, the organic phase is washed with water multiple times and dried with anhydrous sodium sulfate, and finally the organic phase is concentrated to obtain benzamide and its derivatives.

[0043] The structural formulas of the benzamide and its derivatives prepared in the following examples of the present invention are as follows:

[0044]

[0045] To further understand the present invention, the preparation method of the α-hydroxy-β-dicarbonyl derivative provided by the present invention will be described in detail below in conjunction with examples. The protection scope of the present invention is not limited by the following examples.

[0046] Example 1

[0047] A preparation method of a benzamide and its derivative (Compound 3a), the structure and preparation method are as follows:

[0048] Method 1:

[0049]

[0050] The specific steps are as follows: Weigh 3-(p-tolyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), and iron(III) bromide (0.02 mmol) into a 25 mL photoreaction tube, add a magnetic stir bar, and after displacing the air with high-purity nitrogen three times, add 1,2-dichloroethane (3 mL) to the flask under nitrogen protection. At room temperature, irradiate with 18 W blue LED light for 16 hours. Monitor the reaction by TLC. After the reaction is completed, cool the flask to room temperature, add 10 mL of saturated brine to the system, stir to quench the reaction; extract with dichloromethane (10 mL × 3), combine the organic phases, remove the solvent using a rotary evaporator to obtain the crude product; load the crude product onto silica gel, and perform column chromatography purification using a mobile phase of petroleum ether:ethyl acetate = 1:1 (volume ratio) to obtain 4-methylbenzamide as a white solid with an isolated yield of 84%.

[0051] Structure identification of compound 3a:

[0052] Nuclear magnetic resonance data:

[0053] 1 H NMR (500 MHz, Chloroform-d) δ 7.71 (d, J = 8.1 Hz, 2H), 7.24 (d, J = 7.9 Hz, 2H), 5.98 (s, 2H), 2.40 (s, 3H).

[0054] 13 C NMR (126 MHz, Chloroform-d) δ 169.41, 142.53, 130.51, 129.27, 127.38, 21.46.

[0055] For compound 3a 1 the H NMR 13 and C NMR are as Figure 1 , as Figure 2 shown. The analysis results indicate that the obtained target product is correct.

[0056] Example 2

[0057] A preparation method of a benzamide and its derivative (compound 3c), and its structure and preparation method are as follows:

[0058]

[0059] The specific steps are as follows: 3-(p-chlorophenyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube. A magnetic stir bar was added, and after replacing the gas three times with high-purity nitrogen, 1,2-dichloroethane (3 mL) was added to the flask under nitrogen protection. At room temperature, it was irradiated with 18 W LED blue light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring; it was extracted with dichloromethane (10 mL×3), the organic phases were combined, and the solvent was removed by a rotary evaporator to obtain the crude product; the crude product was loaded on silica gel, and column chromatography purification was carried out using a eluent with a volume ratio of petroleum ether:ethyl acetate = 1:1 to obtain 4-chlorobenzamide, a white solid, with a separation yield of 93%.

[0060] Structure identification of compound 3c:

[0061] Nuclear magnetic resonance data:

[0062] 1 H NMR(500MHz,Chloroform-d)δ7.75(d,J=8.5Hz,2H),7.43(d,J=8.5Hz,2H),5.96(s,2H).

[0063] 13 C NMR(126MHz,Chloroform-d)δ168.22,138.37,131.72,128.92,128.79.

[0064] For compound 3c 1 the H NMR 13 and C NMR data analysis results indicate that the obtained target product is correct.

[0065] Example 3

[0066] A preparation method of a benzamide and its derivative (compound 3k), and its structure and preparation method are as follows:

[0067]

[0068] The specific steps are as follows: 3-(m-tolyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacolborane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube with a magnetic stirrer. After purging with high-purity nitrogen three times, 1,2-dichloroethane (3 mL) was added to the flask under nitrogen protection. At room temperature, the reaction was carried out under 18W LED blue light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring. The mixture was extracted with dichloromethane (10 mL × 3), and the organic phases were combined. The solvent was removed by rotary evaporation to obtain the crude product. The crude product was loaded on silica gel, and column chromatography purification was carried out using a solvent mixture of petroleum ether:ethyl acetate = 1:1 (v / v) to obtain 3-methylbenzamide as a white solid with a separation yield of 72%.

[0069] Structure identification of compound 3k:

[0070] Nuclear magnetic resonance data:

[0071] 1 H NMR (500 MHz, Chloroform-d) δ 7.67 (s, 1H), 7.61 (s, 1H), 7.36 (s, 2H), 5.93 (d, J = 152.1 Hz, 2H), 2.43 (s, 3H).

[0072] 13 C NMR (126 MHz, Chloroform-d) δ 169.51, 138.53, 133.30, 132.75, 128.49, 128.13, 124.28, 21.32.

[0073] For compound 3k 1 the 13 analysis results of H NMR and

[0074] Example 4

[0075] A preparation method of a benzamide and its derivative (compound 3t), the structure and preparation method are as follows:

[0076]

[0077] The specific steps are as follows: 3-(o-Trifluoromethylphenyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube. A magnetic stir bar was added, and the tube was purged with high-purity nitrogen three times. Then, under nitrogen protection, 1,2-dichloroethane (3 mL) was added to the flask. At room temperature, the reaction was carried out under 18 W LED blue light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring. The mixture was extracted with dichloromethane (10 mL×3), and the organic phases were combined. The solvent was removed using a rotary evaporator to obtain the crude product. The crude product was loaded onto silica gel, and column chromatography purification was carried out using a mobile phase of petroleum ether:ethyl acetate = 1:1 (v / v) to obtain 2-trifluoromethylbenzamide as a white solid with a separation yield of 75%.

[0078] Structure identification of compound 3t:

[0079] Nuclear magnetic resonance data:

[0080] 1 H NMR(500MHz,Chloroform-d)δ7.71(d,J=8.0Hz,1H),7.61(s,1H),7.60(s,1H),7.58-7.54(m,1H),5.97(d,J=147.5Hz,2H).

[0081] 13 C NMR(126MHz,Chloroform-d)δ169.75,134.98,132.06,130.12,128.61,127.23(q, 2 J CF3 =32.0Hz),126.39(q, 3 J CF3 =4.6Hz),123.53(q, 1 J CF3 =272.2Hz).

[0082] For compound 3t, 1 the analysis results of 13 1H NMR and 13C NMR data indicate that the obtained target product is correct.

[0083] Example 5

[0084] A preparation method of a benzamide and its derivative (compound 3p), the structure and preparation method are as follows:

[0085]

[0086] The specific steps are as follows: 3-(o-methylphenyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube. A magnetic stir bar was added, and the tube was purged with high-purity nitrogen three times. Then, under nitrogen protection, 1,2-dichloroethane (3 mL) was added to the flask. At room temperature, the reaction was carried out under 18 W blue LED light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring. The mixture was extracted with dichloromethane (10 mL × 3), and the organic phases were combined. The solvent was removed using a rotary evaporator to obtain the crude product. The crude product was loaded onto silica gel, and column chromatography purification was carried out using a eluent with a volume ratio of petroleum ether:ethyl acetate = 1:1 to obtain 2-methylbenzamide, a white solid, with a separation yield of 60%.

[0087] Structure identification of compound 3p:

[0088] Nuclear magnetic resonance data:

[0089] 1 H NMR (500 MHz, Chloroform-d) δ 7.47 - 7.45 (m, 1H), 7.34 (td, J = 7.5, 1.5 Hz, 1H), 7.25 - 7.20 (m, 2H), 5.69 - 5.63 (m, 2H), 2.51 (s, 3H).

[0090] 13 C NMR (126 MHz, DMSO-d6) δ 170.94, 137.02, 135.02, 130.36, 129.06, 126.92, 125.85, 19.48.

[0091] For compound 3p 1 the H NMR 13 and C NMR data analysis results indicate that the obtained target product is correct.

[0092] Example 6

[0093] A preparation method of a benzamide and its derivative (compound 3m), and its structure and preparation method are as follows:

[0094]

[0095] The specific steps are as follows: 3-(m-chlorophenyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube. A magnetic stir bar was added, and the tube was purged with high-purity nitrogen three times. Then, under nitrogen protection, 1,2-dichloroethane (3 mL) was added to the flask. At room temperature, the reaction was carried out under 18 W blue LED light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring. The mixture was extracted with dichloromethane (10 mL × 3), and the organic phases were combined. The solvent was removed using a rotary evaporator to obtain the crude product. The crude product was loaded onto silica gel, and column chromatography purification was carried out using a mobile phase of petroleum ether:ethyl acetate = 1:1 (v / v) to obtain 3-chlorobenzamide as a white solid with a separation yield of 74%.

[0096] Structure identification of compound 3m:

[0097] Nuclear magnetic resonance data:

[0098] 1 H NMR (500 MHz, Chloroform-d) δ 7.81 (s, 1H), 7.68 (d, J = 7.7 Hz, 1H), 7.51 (d, J = 7.9 Hz, 1H), 7.40 (t, J = 7.9 Hz, 1H), 6.04 - 5.82 (m, 2H).

[0099] 13 C NMR (126 MHz, Chloroform-d) δ 167.87, 135.13, 134.88, 132.05, 129.96, 127.74, 125.39.

[0100] For compound 3m 1 the H NMR 13 and C NMR data analysis results indicate that the obtained target product is correct.

[0101] Example 7

[0102] A preparation method of a benzamide and its derivative (compound 3o), the structure and preparation method are as follows:

[0103]

[0104] The specific steps are as follows: 3-(m-methoxyphenyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube. A magnetic stir bar was added, and the tube was purged with high-purity nitrogen three times. Then, under nitrogen protection, 1,2-dichloroethane (3 mL) was added to the flask. At room temperature, the reaction was carried out under 18 W LED blue light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring. The mixture was extracted with dichloromethane (10 mL × 3), and the organic phases were combined. The solvent was removed using a rotary evaporator to obtain the crude product. The crude product was loaded onto silica gel, and column chromatography purification was carried out using a eluent with a volume ratio of petroleum ether:ethyl acetate = 1:1 to obtain 3-methoxybenzamide as a white solid with a separation yield of 75%.

[0105] Structure identification of compound 3o:

[0106] Nuclear magnetic resonance data:

[0107] 1 H NMR(500MHz,Chloroform-d)δ7.41-7.40(m,1H),7.36-7.32(m,2H),7.07(dt,J=7.2,2.3Hz,1H),6.10-5.92(m,2H),3.85(s,1H).

[0108] 13 C NMR(126MHz,Chloroform-d)δ169.22,159.88,134.83,129.60,119.16,118.27,112.61,55.45.

[0109] For compound 3o 1 the analysis results of 13 1H NMR and

[0110] Example 8

[0111] A preparation method of a benzamide and its derivative (compound 3r), the structure and preparation method are as follows:

[0112]

[0113] The specific steps are as follows: 3-(o-chlorophenyl)-1,4,2-dioxazol-5-one (0.2 mmol), pinacol borane (0.4 mmol), iron(III) bromide (0.02 mmol) were placed in a 25 mL photoreaction tube. A magnetic stir bar was added, and the tube was purged with high-purity nitrogen three times. Then, under nitrogen protection, 1,2-dichloroethane (3 mL) was added to the flask. At room temperature, the reaction was carried out under 18 W LED blue light for 16 hours. The reaction was monitored by TLC. After the reaction was completed, the flask was cooled to room temperature, 10 mL of saturated brine was added to the system, and the reaction was quenched by stirring. The mixture was extracted with dichloromethane (10 mL × 3), and the organic phases were combined. The solvent was removed using a rotary evaporator to obtain the crude product. The crude product was loaded onto silica gel, and column chromatography purification was carried out using a eluent with a volume ratio of petroleum ether:ethyl acetate = 1:1 to obtain 2-chlorobenzamide, a white solid, with a separation yield of 68%.

[0114] Structure identification of compound 3r:

[0115] Nuclear magnetic resonance data:

[0116] 1 H NMR (500 MHz, DMSO-d6) δ 7.84 (s, 1H), 7.55 (s, 1H), 7.48 - 7.46 (m, 1H), 7.44 - 7.40 (m, 2H), 7.38 - 7.35 (m, 1H).

[0117] 13 C NMR (126 MHz, DMSO-d6) δ 168.05, 137.09, 130.45, 129.56, 129.52, 128.59, 126.92.

[0118] For compound 3r 1 H NMR, 13 The analysis results of 13C NMR data indicate that the obtained target product is correct.

[0119] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. However, such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing benzamide and its derivatives, characterized in that, The steps are as follows: in the presence of a solvent, under photochemical catalysis with a wavelength range of 400 - 480 nm, using iron bromide as a catalyst, reacting 3-phenyl-1,4,2-dioxazol-5-one and its derivatives with pinacol borane to obtain benzamide and its derivatives. The reaction formula is as follows: Among them, the R1 group is selected from one of hydrogen, halogen, C 1～10 alkyl, C 1～10 alkoxy, and nitro.

2. The preparation method of the benzamide and its derivatives according to claim 1, characterized in that, The light intensity range of the light source selected for the photochemical catalysis is 5 - 18 W.

3. The preparation method of the benzamide and its derivatives according to claim 1, characterized in that, The molar ratio of the 3-phenyl-1,4,2-dioxazol-5-one and its derivatives to pinacol borane is 1:

2.

4. The preparation method of the benzamide and its derivatives according to claim 1, characterized in that, The solvent is one or more of water, methanol, ethanol, acetonitrile, benzene, toluene, tetrahydrofuran, ethyl acetate, dimethyl sulfoxide, N,N-dimethylformamide, acetone, 1,2-dichloroethane, and dichloromethane.

5. The preparation method of the benzamide and its derivatives according to claim 1, characterized in that, The reaction is carried out in air or an inert atmosphere, and the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

6. The preparation method of the benzamide and its derivatives according to claim 1, characterized in that, After the reaction is completed, the reaction solution is extracted with dichloromethane, washed with water several times using the organic phase and dried with anhydrous sodium sulfate. Finally, the organic phase is concentrated to obtain benzamide and its derivatives.

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