Method for synthesizing beta-lactam and bicyclo [2, 1, 1] compound through visible light catalysis

Abstract

The invention discloses a method for synthesizing beta-lactam and bicyclo [2, 1, 1] compounds through visible light catalysis, which comprises the following steps: in a nitrogen atmosphere, taking a diolefin substrate as a raw material, taking an LED lamp as a light source, carrying out cyclization reaction at 10-40 DEG C in the presence of a photosensitizer and a solvent, and separating and purifying the product through a thin layer chromatography to obtain the target product beta-lactam and bicyclo [2, 1, 1] compounds. 1] Compounds. According to the invention, triplet state energy transfer and free radical cyclization processes are carried out on a diolefin substrate at normal temperature, and beta-lactam and a bicyclo [2, 1, 1] compound are respectively constructed in parallel and cross cycloaddition modes. The method is mild in condition, good in atom economy and simple to operate, and has economic practicability and industrial production prospects.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and in particular relates to a method for synthesizing beta-lactam and bicyclic [2,1,1] compounds by using visible light catalysis. Background Art

[0002] In the field of medicinal chemistry research, β-lactams and bicyclic [2,1,1] compounds are two very important molecular structures. The former is the main skeleton of antibiotics, and the latter is the core structure of bioisosteres. The early synthesis methods of β-lactams mainly include Staudinger reaction, Minnich amidation reaction, Kinugasa reaction, CH bond activation reaction, free radical cyclization, etc.; the synthesis methods of bicyclic [2,1,1] compounds mainly include the ring-opening addition reaction of bicyclo [1,1,0] cyclobutane, intramolecular double bond cross-cycloaddition reaction, etc. These reactions have some limitations, such as the Staudinger reaction requires highly active enone precursors (A. Porcheddu, RSC Adv. 2016, 6, 38553), CH bond activation requires substrates with specific directing groups (Y. Tang, Angew. Chem., Int. Ed. 2017, 56, 6942), and carbene insertion reactions require expensive noble metal catalysts (MP Doyle, Chem. Sci. 2015, 6, 2196), etc. Photocatalysis is widely used in various organic synthesis methods due to its mild reaction conditions, good selectivity, and high atom economy. We envision the simultaneous construction of β-lactam and bicyclic [2,1,1] compounds under visible light. Therefore, it is necessary to develop a facile method to prepare functionalized β-lactam and bicyclic [2,1,1] compound skeletons. We describe a visible light-activated, inexpensive, and green catalytic system for the synthesis of β-lactam and bicyclic [2,1,1] compounds. Summary of the invention

[0003] The present invention provides a method for synthesizing β-lactam and bicyclic [2,1,1] compounds by visible light catalysis. The present invention uses cheap small molecule ketone as a photosensitizer and a visible light LED lamp as a light source to cause a diene substrate to undergo triplet energy transfer and free radical cyclization at room temperature, and constructs β-lactam and bicyclic [2,1,1] compounds respectively by parallel and cross cycloaddition. The present invention has mild conditions, good atom economy, simple operation, and has economical practicality and industrial production prospects.

[0004] The method for synthesizing β-lactam and bicyclic [2,1,1] compound catalyzed by visible light of the present invention adopts a one-step method to prepare the target product, which specifically comprises the following steps:

[0005] Under nitrogen protection, with diene substrate as raw material, benzophenone as photosensitizer, dry acetonitrile as solvent, visible light LED lamp as light source, cyclization reaction occurs between 10 ~ 40 ℃, and the reaction time is controlled at 6 ~ 18 h. Direct vacuum concentration, separation and purification of the product by thin layer chromatography, to obtain the target product β-lactam and bicyclic [2,1,1] compound.

[0006] The reaction route is as follows:

[0007]

[0008] Where R 1 is selected from aryl or substituted aryl, wherein the substituent includes alkyl, alkoxy, halogen, nitro, heteroatom, etc.; R 2 is selected from a hydrogen atom or a phenyl group.

[0009] The selected photosensitizer is benzophenone, the solvent is dry acetonitrile, and the LED lamp is a Kessil brand 390 nm visible light lamp.

[0010] The molar ratio of the diene substrate to benzophenone is controlled to be 1:0.01 to 1:0.10.

[0011] The solvent was dry acetonitrile, and the substrate concentration was controlled at 0.05 M ~ 0.2 M.

[0012] The frequency of the 390 nm LED light is controlled from 10 to 40 W.

[0013] The structural formulas of the β-lactam and bicyclic [2,1,1] compounds prepared by the method of the present invention include the following:

[0014] β-Lactam:

[0015]

[0016] Bicyclic [2,1,1] compounds:

[0017]

[0018] In view of the problems existing in the prior art, the present invention adopts visible light catalysis to provide a method for preparing β-lactam and bicyclic [2,1,1] compounds with mild reaction conditions, high atom economy, safety and high efficiency. The present invention adopts a one-pot method, mild reaction conditions, simple operation, high yield, economical practicality and industrial production prospects. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further analyzed and explained below through specific embodiments.

[0020] 1. Condition screening

[0021] SM represents the remaining raw material; the yield is calculated by adding a quantitative internal standard 1,1,2,2-dichloroethane and calculating the NMR yield by comparing the characteristic peak areas of the NMR spectrum.

[0022]

[0023] Screening of photosensitizers confirmed that benzophenone had the best effect.

[0024]

[0025] After screening the reaction solvents, acetonitrile was confirmed to be the optimal solvent.

[0026]

[0027] Control experiments showed that the reaction requires a photosensitizer and is sensitive to oxygen and concentration.

[0028] (II) Preparation of diene substrates

[0029]

[0030] Step 1: Add hydroxylamine hydrochloride (1.2 equiv), sodium acetate (1.2 equiv), raw ketone (1.0 equiv, 60 mmol) to a dry 250 mL round-bottom flask, and add solvent methanol (0.5 M). Stir at room temperature for 2 h and monitor the reaction system using a TLC plate. After the reaction is completed, vacuum concentrate to remove the methanol solvent, then extract with ethyl acetate three times, wash the obtained organic phase with saturated brine, and then dry with anhydrous sodium sulfate. After filtration and vacuum concentration, the crude product solid is obtained, which is directly used in the next step without further purification.

[0031]

[0032] Step 2: Add ferrous acetate (5 mol%), potassium iodide (0.4 equiv), sodium dithionite (2 equiv), and the oxime prepared in the previous step (1.0 equiv, 30 mmol) to a dry 500 mL round-bottom flask, seal it with a rubber stopper, replace the gas with a double-row nitrogen tube three times, and insert a balloon filled with nitrogen. Then add the solvent 1,2-dichloroethane (0.2 M, 150 mL), acetic anhydride (2.1 equiv), and acetic acid (3.0 equiv) to the flask in sequence, place the flask in a 65°C reaction environment, react for about 2.5 h, and use a TLC plate to detect the reaction system during this period. After the reaction is completed, place the flask in a room temperature environment to cool to room temperature, slowly add saturated sodium bicarbonate solution to it, and shake while adding until no obvious bubbles are generated. The product was extracted with dichloromethane three times, and the obtained organic phase was washed with saturated brine, then dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo. The enamine product was separated by column chromatography, and the eluent was a mixture of petroleum ether and ethyl acetate in a volume ratio of 3:1.

[0033]

[0034] Step 3A: Add the enamine prepared in step 2 (1 equiv, 5 mmol) to a dry 100 mL round-bottom flask, seal it with a rubber stopper, replace the gas with a double-row nitrogen gas three times, and insert a balloon filled with nitrogen. Inject the solvent dichloromethane (0.2 M, 25 mL) into the flask and stir it at 0°C for 10 min. Then slowly add triethylamine (3 equiv) dropwise into it and stir it for 10 min after the addition. Extract methacryloyl chloride (2 equiv) and slowly add it dropwise into the flask. After the addition, place the flask at room temperature and react for about 20 h. During this period, the reaction system is detected by TLC plate. After the reaction is completed, water is added to quench it, and it is extracted three times with dichloromethane. The obtained organic phase is washed with saturated brine, dried with anhydrous sodium sulfate, filtered, concentrated in vacuo, and separated by column chromatography to obtain the target product. The eluent is a mixture of petroleum ether and ethyl acetate with a volume ratio of 15:1.

[0035]

[0036] Step 3B: Add 2-phenylacrylic acid (2 equiv, 10 mmol) to a dry 50 mL round-bottom flask, replace the gas with a double-row nitrogen tube three times, and insert a nitrogen balloon for protection. Add solvent dichloromethane (0.5M) to the flask, place it at 0°C, add a drop (0.01~0.02 mL) of N,N-dimethylformamide, and stir for 5 min. Use a syringe to draw oxalyl chloride (1.2 equiv) and slowly add it to the flask. After the addition, place the flask at room temperature and stir for 2 h. After the reaction is completed, vacuum concentrate to remove excess oxalyl chloride, add 5 mL of dichloromethane to dissolve the product for use.

[0037] Step 3C: Take another dry 100 mL round-bottom flask, weigh the enamine prepared in step 2 (1 equiv, 5 mmol) and place it in the flask, seal it with a rubber stopper, replace the gas with a double-row nitrogen tube three times, and insert a balloon filled with nitrogen. Inject the solvent dichloromethane (0.2 M, 25 mL) into the flask and stir it at 0°C for 10 min. Then slowly add triethylamine (3 equiv) dropwise into it and stir it for 10 min after the addition. Draw 2-phenylacryloyl chloride solution with a syringe and slowly add it dropwise into the 100 mL flask and stir. After the addition, place the flask at room temperature and react for about 20 h. During this period, the reaction system is detected by TLC plate. After the reaction is completed, water is added to quench it, and the mixture is extracted three times with dichloromethane. The obtained organic phase is washed with an equal volume of saturated brine, dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo, and then separated by column chromatography to obtain the target product. The eluent is a mixture of petroleum ether and ethyl acetate in a volume ratio of 15:1.

[0038] The following specific diene substrates were prepared by the above reaction steps:

[0039]

[0040] Embodiment 1:

[0041]

[0042] Prepare a dry and clean 10 mL Schlenk tube, add a magnetic particle of appropriate size, weigh substrate 1a (0.2 mmol, 1 equiv) and benzophenone (0.0011 g), replace the gas with double-row nitrogen three times, add solvent acetonitrile (0.1 M) under nitrogen flow, seal it and place it under 390 nm LED light, react at 30°C for 12 h. After the reaction is completed, directly concentrate in vacuum. After dissolving the product with 1 mL of dichloromethane, the sample solution was evenly spread on a thin layer silica gel plate with a pointed dropper, and the sample was developed with a developing agent of petroleum ether:ethyl acetate in a volume ratio of 10:1. After the development, the product color band outline was lightly drawn with a pencil, and the two product bands were scraped off with a scraper. The silica gel particles of the bands were washed and filtered with dichloromethane, and then concentrated under reduced pressure to remove the solvent, and the target products β-lactam 2a and bicyclo [2,1,1] compound 3a were obtained. Both were colorless oily liquids with a yield of 73% for 2a and 4% for 3a.

[0043] 2a NMR data are as follows:

[0044] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.43-7.21 (m, 5H), 3.04 (m,1H), 2.55 (m, 1H), 2.50 (m, 1H), 2.49 (s, 3H), 2.22 (m, 1H), 1.10 (s, 3H).

[0045] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.57, 168.10, 134.84,128.64, 127.89, 126.04, 66.11, 61.01, 26.41, 26.33, 24.49, 13.00.

[0046] 3a NMR data are as follows:

[0047] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.41-7.23 (m, 5H), 2.73 (d,1H), 2.72 (d, 1H), 2.43 (d, 1H), 2.42 (d, 1H), 2.38 (s, 3H), 1.37 (s, 3H).

[0048] Embodiment 2:

[0049]

[0050] 1b was used as the starting substrate to prepare the target products 2b and 3b, and the preparation method was the same as that in Example 1. Both were colorless oily liquids, and the yields of 2b and 3b were 83% and 5%, respectively.

[0051] 2b NMR data are as follows:

[0052] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.24 (m, 2H), 7.08 (m, 2H), 2.99 (m, 1H), 2.56 (m, 1H), 2.50 (m, 1H), 2.49 (s, 3H), 2.22 (m, 1H), 1,11(s, 3H).

[0053] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.44, 168.09, 163.54,161.09, 130.84, 127.88, 115.76, 115.54, 65.55, 61.06, 26.49, 26.35, 24.44,12.94.

[0054] 19 F NMR (376 MHz, Chloroform-d): δ (ppm) = -114.19.

[0055] 3b NMR data are as follows:

[0056] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.23 (m, 2H), 7.03 (m, 2H), 2.72 (d, 1H), 2.71 (d, 1H), 2.42 (d, 1H), 2.40 (d, 1H), 2.39 (s, 3H), 1,37(s, 3H).

[0057] 19 F NMR (376 MHz, Chloroform-d): δ (ppm) = -113.71.

[0058] Embodiment 3:

[0059]

[0060] 1c was used as the starting substrate to prepare the target products 2c and 3c. The preparation method was the same as that in Example 1, except that the photosensitizer was adjusted to 6 mol%. Both products were colorless oily liquids, and the yields of 2c and 3c were 79% and 10%, respectively.

[0061] 2c NMR data are as follows:

[0062] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.51 (d, 2H), 7.14 (d, 2H), 2.98 (m, 1H), 2.54 (m, 1H), 2.50 (m, 1H), 2.49 (s, 3H), 2.22 (m, 1H), 1,10(s, 3H).

[0063] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.15, 168.01, 134.04,131.81, 127.83, 122.04, 65.60, 61.12, 26.34, 26.28, 24.42, 12.97.

[0064] 3C NMR data are as follows:

[0065] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.48 (d, 2H), 7.12 (d, 2H), 2.71 (d, 1H), 2.70 (d, 1H), 2.41 (d, 1H), 2.40 (d, 1H), 2.38 (s, 3H), 1,37(s, 3H).

[0066] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 179.37, 169.35, 136.01,131.33, 129.27, 128.11, 67.94, 54.36, 49.59, 26.49, 25.86, 13.16.

[0067] Embodiment 4:

[0068]

[0069] 1d was used as the starting substrate to prepare the target products 2d and 3d. The preparation method was the same as that in Example 1, except that the TLC developing solvent was adjusted to a mixture of petroleum ether and ethyl acetate in a volume ratio of 4:1. Both products were light yellow oils with a yield of 31% for 2d and 19% for 3d.

[0070] The 2D NMR data are as follows:

[0071] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 8.26 (d, 2H), 7.44 (d, 2H), 3.06 (m, 1H), 2.60 (m, 1H), 2.54 (m, 1H), 2.53 (s, 3H), 2.31 (m, 1H), 1,13(s, 3H).

[0072] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 170.42, 167.99, 147.40,142.32, 127.10, 123.94, 65.30, 61.91, 54.40, 26.44, 24.38,13.03.

[0073] The 3D NMR data are as follows:

[0074] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 8.22 (d, 2H), 7.42 (d, 2H), 2.77 (d, 1H), 2.76 (d, 1H), 2.49 (d, 1H), 2.48 (d, 1H), 2.40 (s, 3H), 1,41(s, 3H).

[0075] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 178.78, 169.41, 147.36,144.09, 127.28, 123.52, 67.31, 58.77, 49.85, 26.38, 25.53,13.10.

[0076] Embodiment 5:

[0077]

[0078] 1e was used as the starting substrate to prepare the target products 2e and 3e, and the preparation method was the same as that in Example 1. The product was a colorless oil, and the yield of 2e was 79%, and that of 3e was 0%.

[0079] 2e NMR data are as follows:

[0080] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.18 (m, 2H), 6.91 (m, 2H), 3.79 (s, 3H), 2.99 (m, 1H), 2.52 (m, 1H), 2.48 (s, 1H), 2.46 (s, 3H), 2.18(m, 1H), 1.10(s, 3H).

[0081] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.75, 168.11, 159.20,127.34, 126.94, 114.06, 65.93, 60.88, 55.28, 26.41, 26.31,24.46, 12.96.

[0082] Embodiment 6:

[0083]

[0084] 1f was used as the starting substrate to prepare the target products 2f and 3f, and the preparation method was the same as that in Example 1. The product was a light green oil, and the yield of 2f was 43% and that of 3f was 1%.

[0085] The 2f NMR data are as follows:

[0086] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.62-7.57 (m, 4H), 7.44 (t,2H), 7.37-7.32 (m, 3H), 3.07 (m, 1H), 2.57 (m, 1H), 2.53 (m, 1H), 2.51 (s,3H), 2.24 (m, 1H), 1.14 (s, 3H).

[0087] 13C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.54, 168.15, 140.76,140.46, 133.83, 128.83, 127.50, 127.40, 127.10, 126.53, 65.99, 61.18, 26.43,26.41, 24.51, 13.08.

[0088] The 3f NMR data are as follows:

[0089] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.82-7.33 (m, 9H), 2.76 (d,1H), 2.75 (d, 1H), 2.45 (d, 1H), 2.44 (d, 1H), 2.41 (s, 3H), 1.39 (s, 3H).

[0090] Embodiment 7:

[0091]

[0092] 1g was used as the starting substrate to prepare the target products 2g and 3g, and the preparation method was the same as that in Example 1. The product was a colorless oil, and the yield of 2g was 73%, and that of 3g was 4%.

[0093] 2g NMR data are as follows:

[0094] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.90-7.80 (m, 3H), 7.76 (d,1H), 7.53-7.46 (m, 2H), 7.35 (dd, 1H), 3.21 (m, 1H), 2.62 (m, 1H), 2.55 (m,1H), 2.54 (s, 3H), 2.27 (m, 1H), 1.13 (s, 3H).

[0095] 13C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.60, 168.13, 133.19,132.80, 132.29, 128.52, 128.11, 127.64, 126.48, 126.39, 125.77, 123.33,66.23, 61.30, 26.46, 26.13, 24.51, 13.07.

[0096] 3g NMR data are as follows:

[0097] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.94-7.37 (m, 7H), 2.81 (d,1H), 2.80 (d, 1H), 2.49 (d, 1H), 2.48 (d, 1H), 2.40 (s, 3H), 1.40 (s, 3H).

[0098] Embodiment 8:

[0099]

[0100] 1h was used as the starting substrate to prepare the target products 2h and 3h, and the preparation method was the same as that in Example 1. The product was a colorless oil, and the yield of 2h was 42% and that of 3h was 14%.

[0101] 2h NMR data are as follows:

[0102] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.24-7.16 (m, 3H), 7.10-7.04 (m, 1H), 2.95-2.80 (m, 2H), 2.75-2.60 (m, 2H), 2.48 (s, 3H), 2.03 (m,1H), 1.85 (q, 1H), 1.79 (m, 1H), 1.05 (s, 3H).

[0103] 13C NMR (100 MHz, Chloroform-d): δ (ppm) = 171.74, 167.79, 133.19,139.31, 130.24, 128.43, 127.68, 126.64, 124.91, 64.46, 60.16, 36.04, 31.87,27.95, 27.39, 24.37, 13.15.

[0104] Embodiment 9:

[0105]

[0106] 1i was used as the starting substrate to prepare the target products 2i and 3i, and the preparation method was the same as that in Example 1. The product 2i was a yellow-green solid, and 3i was a white solid, with a yield of 49% for 2i and 27% for 3i.

[0107] 2i NMR data are as follows:

[0108] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.83-7.70 (m, 3H), 7.65 (d,1H), 7.45 (t, 2H), 7.22-7.14 (m, 5H), 7.14-7.08 (dd, 1H), 3.38 (m, 1H), 2.94-2.76 (m, 3H), 2.57 (s, 3H).

[0109] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 169.68, 168.25, 133.37,132.94, 132.77, 132.10, 128.57, 128.18, 127.79, 127.61, 126.72, 126.48,126.38, 126.28, 123.68, 68.76, 67.94, 27.82, 26.80, 24.74.

[0110] 3i NMR data are as follows:

[0111] 1H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.89-7.80 (m, 3H), 7.76 (d,1H), 7.52-7.41 (m, 5H), 7.40-7.30 (m, 3H), 3.26 (d, 1H), 3.25 (d, 1H), 2.89 (d, 1H), 2.87 (d, 1H), 2.44 (s, 3H).

[0112] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 177.52, 169.36, 134.37,134.16, 132.99, 132.94, 128.70, 128.07, 128.02, 127.90, 127.88, 127.01,126.42, 126.38, 124.97, 124.56, 67.91, 56.35, 54.12, 26.01.

[0113] Embodiment 10:

[0114]

[0115] 1j was used as the starting substrate for the reaction to prepare the target products 2j and 3j, and the preparation method was the same as that in Example 1. The product 2j was a colorless oil, and 3j was a white solid, with a yield of 42% for 2j and 26% for 3j.

[0116] 2j NMR data are as follows:

[0117] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.29-7.08 (m, 10H), 3.22(m, 1H), 2.87-2.78 (m, 2H), 2.73 (m, 1H), 2.55 (s, 3H).

[0118] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 169.67, 168.18, 134.53,133.28, 132.77, 128.51, 128.34, 127.94, 127.77, 126.80, 126.52, 68.74, 67.82,27.44, 26.93, 24.71.

[0119] 3j NMR data are as follows:

[0120] 1 H NMR (400 MHz, Chloroform-d): δ (ppm) = 7.46-7.27 (m, 10H), 3.17(d, 1H), 3.16 (d, 1H), 2.81 (d, 1H), 2.80 (d, 1H), 2.42 (s, 3H).

[0121] 13 C NMR (100 MHz, Chloroform-d): δ (ppm) = 177.49, 169.36, 136.62,134.38, 128.67, 128.27, 128.22, 128.03, 126.99, 126.38, 67.69, 56.28, 53.94,26.04.

[0122] The above description is only a general embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment according to the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for synthesizing β-lactam and bicyclic [2,1,1] compounds using visible light catalysis, characterized in that: In a nitrogen atmosphere, a diene substrate is used as a raw material, in the presence of a photosensitizer and a solvent, and an LED lamp is used as a light source to cause a cyclization reaction, and the product is separated and purified by thin layer chromatography to obtain the target product β-lactam and bicyclic [2,1,1] compound; The reaction route is as follows: ； Where R 1 is selected from aryl or substituted aryl; R 2 is selected from a hydrogen atom or a phenyl group.

2. The method according to claim 1, characterized in that: The photosensitizer is selected from one of thioxanthone and benzophenone.

3. The method according to claim 2, characterized in that: The photosensitizer is benzophenone.

4. The method according to claim 1, characterized in that: The solvent is selected from one of dry ethyl acetate, dichloroethane and acetonitrile.

5. The method according to claim 4, characterized in that: The solvent is acetonitrile.

6. The method according to claim 1, characterized in that: The wavelength of the light source is 390 nm, and the frequency is controlled to be 10 ~ 40 W.

7. The method according to claim 1, characterized in that: The molar ratio of diene substrate to photosensitizer is controlled to be 1:0.01 to 1:0.

10.

8. The method according to claim 1, characterized in that: The reaction temperature is 10 ~ 40℃.

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