Green method for synthesizing 2-arylindole compound through catalyst-free light driving

Abstract

The invention relates to the technical field of 2-arylindole compounds, in particular to a green method for synthesizing a 2-arylindole compound through catalyst-free light driving. In the prior art, the conventional synthesis method of the 2-aryl indole compound has harsh reaction conditions, and generally, an expensive transition metal catalyst is also required to be added as a catalyst. In order to solve the technical problems, the invention provides the green catalyst-free light-driven synthesis method of the 2-arylindole compound, which comprises the following steps: by taking an indole compound and a diaryl iodonium salt compound as initial reaction raw materials, carrying out blue light irradiation reaction in a reaction solvent at room temperature, and after the reaction is finished, obtaining the 2-arylindole compound. According to the method, reaction raw materials are easy to obtain, reaction steps are simple, conditions are mild, the method is environmentally friendly, no catalyst or chemical additive needs to be added in the reaction process, and the method has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of 2-arylindole compounds, and specifically relates to a green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst. Background Art

[0002] As a class of core structural units, 2-arylindole compounds are widely present in anti-cancer drugs (such as Sunitinib), anti-inflammatory molecules, and organic light-emitting diode (OLED) materials. The research on their efficient and green synthesis methods has great strategic significance for the fields of medicine, health, and materials science. However, the current mainstream synthetic routes in the industry all have irreconcilable technical bottlenecks, seriously restricting the large-scale application and sustainable development of such compounds. Currently, industrial synthesis mainly relies on two types of methods: transition metal catalysis and metal-free oxidation.

[0003] Although the transition metal catalysis method using the traditional palladium / copper-catalyzed indole C-H arylation reaction (such as coupling with aryl halides) has been industrially applied, its inherent defects are significant:

[0004] (1) It is difficult to remove metal residues (palladium residue > 50 ppm, exceeding the ICH Q3D drug safety limit of ≤ 10 ppm);

[0005] (2) It requires expensive ligands (such as phosphine ligands) and inert gas protection;

[0006] (3) Poor regioselectivity control (C2 / C3 ratio is only 85:15, Org. Lett. 2019, 21, 8045), making it difficult to meet the requirements for high-purity drug intermediates.

[0007] To avoid metal contamination, metal-free methods represented by high-temperature indole-aryl Grignard reagent coupling (> 110 °C) or persulfate oxidation radical coupling (J. Org. Chem. 2020, 85, 1236) have been developed, but new problems have emerged:

[0008] (1) High-temperature conditions are likely to result in an E factor (waste mass / product mass) > 30, and persulfate oxidants will produce a large amount of sulfate by-products, violating the principles of green chemistry;

[0009] (2) Strong oxidation conditions are prone to side reactions, reducing the atom utilization rate.

[0010] Although the strategy of activating aryl iodides with photosensitizers developed in recent years (such as the Ru(bpy)3Cl2 system, Nat. Commun. 2023, 14, 3218) has partially improved selectivity, it still faces the following problems:

[0011] (1) Catalyst cost and recovery challenges: The unit price of ruthenium complexes is as high as $500 per gram, and it is difficult to separate and recover them from the products.

[0012] (2) Dependence on base additives: Strong bases such as DBU need to be added additionally to promote the formation of complexes (Org. Lett. 2023, 25, 1234), increasing the complexity of post-treatment.

[0013] Based on the above analysis, it can be seen that the existing technology system cannot simultaneously meet the following core requirements:

[0014] Metal-free residue: Avoid catalyst contamination to meet drug regulatory standards;

[0015] Room temperature operation: Reduce energy consumption and simplify process equipment;

[0016] High regioselectivity: Ensure exclusive arylation at the C2 position (>98:2);

[0017] Atom economy: Minimize the generation of by-products and achieve solvent recycling. Summary of the Invention

[0018] The problem in the existing technology is that for the conventional synthesis methods of 2-arylindole compounds in the existing technology, the reaction conditions are harsh, and expensive transition metal catalysts, phosphine ligands or strong bases such as DBU usually need to be added during the reaction process, which greatly affects the purity of the target product. To address the above technical problems, the present invention provides a green method for the catalyst-free photo-driven synthesis of 2-arylindole compounds, which uses indole compounds and diaryliodonium salt compounds as starting reaction materials, and performs a blue light irradiation reaction at room temperature in a reaction solvent. After the reaction is completed, 2-arylindole compounds are obtained.

[0019] The chemical structural general formula of the 2-arylindole compounds is represented as follows:

[0020]

[0021] In the above chemical structural general formula, R 1 is a substituent at any position on the benzene ring, and R 1 is selected from one of hydrogen, alkyl, alkoxy, halogen, and cyano; R 2 is alkyl; R 3 is one of acetyl and benzoyl; R 4 is a substituent at any position on the benzene ring, and R 4 is selected from one of hydrogen, alkyl, and halogen.

[0022] Preferably, the structural general formula of the indole compounds is represented as follows:

[0023]

[0024] In the above general chemical structure formula, R 1 is at any position on the benzene ring, and R 1 is selected from one of hydrogen, alkyl, alkoxy, halogen, and cyano; R 2 is alkyl; R 3 is one of acetyl and benzoyl.

[0025] Preferably, the general structure formula of the diaryliodonium salt compounds is represented as follows:

[0026]

[0027] R 4 is at any position on the benzene ring, and R 4 is selected from one of hydrogen, alkyl, and halogen.

[0028] Preferably, the reaction solvent includes one or more of 1,4-dioxane, tetrahydrofuran, acetonitrile, and 1,2-dichloroethane.

[0029] Preferably, the wavelength of the blue light irradiation is 456 nm.

[0030] Preferably, the time of the blue light irradiation reaction is 10 - 12 h.

[0031] Preferably, the molar ratio of the indole compound to the diaryliodonium salt compound is 2:3.

[0032] Preferably, the power of the blue light irradiation is 6 W, and the vertical distance between the light source and the upper surface of the reaction solvent is 5 - 10 cm.

[0033] Preferably, the dosage ratio among the indole compound, the diaryliodonium salt compound, and the reaction solvent is 0.2 mmol: 0.3 mmol: 2 mL.

[0034] The present invention has the following beneficial effects:

[0035] The present invention provides a green method for the catalyst-free photo-driven synthesis of 2-arylindole compounds, which has the following advantages compared with the prior art:

[0036] All catalysts are abandoned: By using indole (electron donor) and diaryliodonium salt (electron acceptor) to spontaneously form an EDA complex, the C2-arylation is directly initiated by blue light irradiation, that is, no additives such as bases (mainly used to assist in forming the EDA complex), ligands, etc. are required during the reaction process;

[0037] The selectivity bottleneck is broken through: By substituent design (R 3= acetyl group / benzoyl group), directing the aryl radical to attack the C2 position of indole compounds (the 3-position of the indole heterocycle is occupied by an acyl group, and arylation cannot occur on the benzene ring connected to the heterocycle, and the reaction can only occur at the 2-position of the heterocycle);

[0038] Realized room-temperature green synthesis: driven by blue light with a wavelength of 456 nm, and the by-product is only environmentally friendly aryl iodide;

[0039] The method of the present invention has easily available process raw materials, simple reaction steps, a wide substrate scope, and is easy to scale up. Description of the Drawings

[0040] Figure 1 is the 1 H NMR spectrum of compound 3a;

[0041] Figure 2 is the 13 C NMR spectrum of compound 3a;

[0042] Figure 3 is the 1 H NMR spectrum of compound 3b;

[0043] Figure 4 is the 13 C NMR spectrum of compound 3b;

[0044] Figure 5 is the 1 H NMR spectrum of compound 3c;

[0045] Figure 6 is the 13 C NMR spectrum of compound 3c;

[0046] Figure 7 is the 1 H NMR spectrum of compound 3d;

[0047] Figure 8 is the 13 C NMR spectrum of compound 3d;

[0048] Figure 9 is the 1 H NMR spectrum of compound 3e;

[0049] Figure 10 is the 13 C NMR spectrum of compound 3e;

[0050] Figure 11 is the 1 H NMR spectrum of compound 3f;

[0051] Figure 12of compound 3f 13 C NMR spectrum;

[0052] Figure 13 of compound 3g 1 H NMR spectrum;

[0053] Figure 14 of compound 3g 13 C NMR spectrum;

[0054] Figure 15 of compound 3h 1 H NMR spectrum;

[0055] Figure 16 of compound 3h 13 C NMR spectrum;

[0056] Figure 17 of compound 3i 1 H NMR spectrum;

[0057] Figure 18 of compound 3i 13 C NMR spectrum;

[0058] Figure 19 of compound 3j 1 H NMR spectrum;

[0059] Figure 20 of compound 3j 13 C NMR spectrum. Detailed implementation mode

[0060] The present invention will be described in detail below with reference to the embodiments. However, it should be understood that the following embodiments are only examples of the implementation modes of the present invention, rather than limiting the scope of the present invention.

[0061] The optimal reaction process of 2-arylindole compounds (denoted as the standard reaction) is as follows:

[0062] 1-Methyl-3-acetylindole (CAS: 19012-02-03) (denoted as 1a) and diphenyliodonium trifluoromethanesulfonate (denoted as 2a), and the reaction product is denoted as 3a:

[0063]

[0064] In a clean and dry Schlenk reaction tube with a volume of 10 mL, substrate 1a (34.6 mg, 0.2 mmol), 2a (64.5 mg, 0.3 mmol) and 2 mL of acetonitrile were added in sequence. The reaction tube was purged with nitrogen three times, and then irradiated with an LED lamp with a power of 6 W and a wavelength of 456 nm (the illumination distance was 5 cm) at room temperature under nitrogen protection for 12 h. After the reaction was completed, 10 mL of water was added to the Schlenk reaction tube, and after stirring evenly, the reaction product was extracted three times with 10 mL of ethyl acetate. The organic phases were combined, concentrated, and then purified by silica gel (200 mesh) column chromatography using petroleum ether and ethyl acetate as eluents (the volume ratio of petroleum ether to ethyl acetate was 5:1) to obtain the target product with a yield of 69%.

[0065] Based on the standard reaction, certain specific process parameters were adjusted, and the yield of the target product obtained changed significantly. The adjustment of specific process parameters and the yield of the target product are shown in Table 1 and Continued Table 1 below.

[0066] Table 1

[0067] Experiment Number Single Process Parameter Adjustment Situation Yield 1 No Adjustment 69％ 2 LED Light Illumination Wavelength Changed to 390 nm 27％ 3 LED Light Illumination Wavelength Changed to 440 nm 51％ 4 Illumination Intensity Changed to 8 W 62％ 5 Illumination Intensity Changed to 10 W 54％

[0068] Continued Table 1

[0069] Experiment Number Single Process Parameter Adjustment Situation Yield 6 Reaction Solvent Changed to 1,4-Dioxane 35％ 7 Reaction Solvent Changed to Tetrahydrofuran 40％ 8 Reaction Solvent Changed to 1,2-Dichloroethane 46％ 9 Dosage of 2a Changed to 0.2 mmol 51％ 10 Dosage of 1a Changed to 0.1 mmol 62％ 11 Usage of Acetonitrile Changed to 0.2 mL 23％ 12 Usage of Acetonitrile Changed to 1 mL 40％ 13 Reaction Time Changed to 10 h 63％ 14 Reaction Time Changed to 24 h 67％ 15 No Illumination 0 16 <![CDATA[Additional addition of fac-Ir(ppy)3 photocatalyst (the addition amount is 0.3% of the molar amount of 1a)]]> 69％ 17 <![CDATA[Add an additional Ru(bpy)3·2PF6 photocatalyst (the addition amount is 0.3% of the molar amount of 1a)]]> 66％

[0070] Experiments 1-5 in Table 1 and Continued Table 1 investigated the effects of different light sources and intensities on the yield of the target product. It can be seen from the experimental data that blue light has a good promoting effect on this reaction, and the effect is the best when the wavelength is 456 nm. When using purple light, the yield drops significantly. When the illumination intensity is 6 W, the reaction requirements have been met, and further increasing the intensity easily leads to a rise in the system temperature, thus generating by-products.

[0071] Experiments 6-8 investigated the effects of different reaction solvents on the yield of the target product. The test comparison results showed that acetonitrile had the best reaction effect as the reaction solvent.

[0072] Experiments 9 and 10 investigated the effects of the molar ratio of reaction raw materials on the yield of the target product. When the molar ratio of the amounts of 1a and 2a was 2:3, the best yield of the target product obtained was 69%. A decrease in the amount of raw material 2a would lead to incomplete reaction, and an excessive amount would generate other by-products, both of which would reduce the yield of the target product.

[0073] Experimental groups 11-12 investigated the effects of the amount of reaction solvent on the yield of the target product. Decreasing and increasing the volume of acetonitrile both led to a decrease in the yield of the target product. An excessive or too low amount of solvent would have a certain impact on the diffusion of reactant molecules in the system and the absorption of light, etc., thereby reducing the yield of the target product.

[0074] In Experiment Groups 13 - 14, the influence of reaction time was investigated. The results showed that a reaction time of 12 h was sufficient. Even if the reaction time was extended, the yield could not be increased, and it might even decrease the yield of the target product due to the formation of by-products.

[0075] In Experiment Groups 15 - 17, the influence of light was investigated. When there was no light irradiation, the reaction could not proceed, indicating that light irradiation was essential. Additionally, even when a photocatalyst was added, the reaction yield did not increase, indicating that this reaction did not require any catalyst and could occur with only light irradiation.

[0076] The reaction processes of Examples 1 - 10 are represented by chemical reaction equations:

[0077]

[0078] The reaction process is as follows:

[0079] In a clean and dry Schlenk reaction tube with a volume of 10 mL, substrate 1 (34.6 mg, 0.2 mmol), substrate 2 (64.5 mg, 0.3 mmol), and 2 mL of acetonitrile were successively added. The reaction tube was purged with nitrogen three times, and then irradiated with an LED lamp with a power of 6 W and a wavelength of 456 nm (the light irradiation distance was 5 cm) at room temperature under nitrogen protection for 12 h. After the reaction was completed, 10 mL of water was added to the Schlenk reaction tube, and after stirring evenly, the reaction product was extracted three times with 10 mL of ethyl acetate. The organic phases were combined, concentrated, and then purified by silica gel (200 mesh) column chromatography using petroleum ether and ethyl acetate as the eluent (the volume ratio of petroleum ether to ethyl acetate was 5:1) to obtain the target product.

[0080] The target product obtained in Example 1 was designated as Product 3a (the same as the product obtained in the standard experiment), and the yield was 69%. The structural formula is as follows:

[0081]

[0082] The characterization data of Product 3a are as follows:

[0083] 1 H NMR (400 MHz, CDCl3) δ 8.52 - 8.49 (m, 1H), 7.58 - 7.54 (m, 3H), 7.45 - 7.41 (m, 2H), 7.38 - 7.33 (m, 3H), 3.51 (s, 3H), 1.97 (s, 3H).

[0084] 1313C NMR (101 MHz, CDCl3) δ 194.6, 146.4, 136.6, 132.2, 130.2, 129.6, 128.8, 126.6, 123.4, 122.8, 122.8, 115.9, 109.4, 30.8, 30.2.

[0085] The target product obtained in Example 2 was designated as Product 3b, with a yield of 76%, and its structural formula is as follows:

[0086]

[0087] The characterization data of Product 3b are as follows:

[0088] 1 1H NMR (400 MHz, CDCl3) δ 8.53 - 8.49 (m, 1H), 7.59 - 7.52 (m, 3H), 7.46 - 7.42 (m, 2H), 7.40 - 7.31 (m, 3H), 5.64 - 5.53 (m, 1H), 5.00 - 4.92 (m, 2H), 3.98 - 3.94 (m, 2H), 2.40 (q, J = 7.3 Hz, 2H), 1.93 (s, 3H).

[0089] 13 13C NMR (101 MHz, CDCl3) 194.7, 146.0, 135.7, 133.8, 132.2, 130.4, 129.7, 128.8, 126.9, 123.3, 122.9, 122.8, 117.7, 116.2, 109.8, 43.6, 34.0, 30.2.

[0090] The target product obtained in Example 3 was designated as Product 3c, with a yield of 70%, and its structural formula is as follows:

[0091]

[0092] The characterization data of Product 3c are as follows:

[0093] 1 1H NMR (400 MHz, CDCl3) δ 8.37 (d, J = 8.3 Hz, 1H), 7.55 - 7.53 (m, 3H), 7.43 - 7.41 (m, 2H), 7.18 - 7.16 (m, 2H), 5.64 - 5.54 (m, 1H), 5.00 - 4.92 (m, 2H), 3.92 (dd, J = 8.8, 6.7 Hz, 2H), 2.53 (s, 3H), 2.39 (q, J = 7.4 Hz, 2H), 1.91 (s, 3H).

[0094] 1313C NMR (101 MHz, CDCl3) δ 194.7, 145.6, 136.0, 133.9, 133.3, 132.3, 130.4, 129.6, 128.7, 124.6, 124.4, 122.6, 117.6, 116.1, 109.7, 43.4, 34.0, 30.1, 21.9。

[0095] The target product obtained in Example 4 is denoted as Product 3d, and the yield is 57%. The structural formula is as follows:

[0096]

[0097] The characterization data of Product 3d are as follows:

[0098] 1 1H NMR (400 MHz, CDCl3) δ 8.43 (d, J = 8.6 Hz, 1H), 7.57 - 7.55 (m, 3H), 7.44 - 7.42 (m, 2H), 7.36 (s, 1H), 7.28 (dd, J = 8.6, 1.8 Hz, 1H), 5.61 - 5.51 (m, 1H), 5.00 - 4.91 (m, 2H), 3.91 (t, J = 7.7 Hz, 2H), 2.38 (q, J = 7.4 Hz, 2H), 1.89 (s, 3H).

[0099] 13 13C NMR (101 MHz, CDCl3) δ 194.6, 146.6, 136.2, 133.4, 131.6, 130.3, 129.9, 129.2, 128.9, 125.4, 124.0, 123.3, 118.0, 116.1, 109.8, 43.6, 33.9, 30.1.

[0100] The target product obtained in Example 5 is denoted as Product 3e, and the yield is 68%. The structural formula is as follows:

[0101]

[0102] The characterization data of Product 3e are as follows:

[0103] 1 1H NMR (400 MHz, CDCl3) δ 8.59 (d, J = 8.3 Hz, 1H), 7.71 (s, 1H), 7.60 - 7.54 (m, 4H), 7.45 - 7.43 (m, 2H), 5.60 - 5.50 (m, 1H), 5.01 - 4.92 (m, 2H), 3.99 (t, J = 7.6 Hz, 2H), 2.39 (q, J = 7.4 Hz, 2H), 1.91 (s, 3H).

[0104] 13 C NMR (101 MHz, CDCl3) δ 194.5, 148.9, 134.8, 133.0, 131.0, 130.3, 130.1 (2C), 129.1, 125.6, 123.9, 120.1, 118.4, 116.5, 114.6, 106.0, 43.9, 34.0, 30.2.

[0105] The target product obtained in Example 6 was designated as Product 3f, with a yield of 78%, and its structural formula is as follows:

[0106]

[0107] The characterization data of Product 3f are as follows:

[0108] 1 H NMR (400 MHz, CDCl3) δ 8.63 (s, 1H), 7.60 - 7.54 (m, 3H), 7.48 - 7.34 (m, 4H), 5.60 - 5.50 (m, 1H), 5.01 - 4.90 (m, 2H), 3.92 - 3.89 (m, 2H), 2.39 - 2.34 (m, 2H), 1.88 (s, 3H).

[0109] 13 C NMR (101 MHz, CDCl3) δ 194.3, 147.4, 134.6, 133.3, 131.3, 130.၂, 130.၁, 129.၀, 127.၂, 126.၉, 126.၄, 124.၂, 118.၂, 115.၆, 11၁.၃, 43.၈, 33.၉, 3၀.၀.

[0110] The target product obtained in Example 7 was designated as Product 3g, with a yield of 71%, and its structural formula is as follows:

[0111]

[0112] The characterization data of Product 3g are as follows:

[0113] 1 H NMR (400 MHz, CDCl3) δ 8.31 (s, 1H), 7.54 - 7.51 (m, 3H), 7.42 - 7.40 (m, 2H), 7.၂၄ (s, 1H), 7.၁၄ (d, J = ၈.၄ Hz, 1H), 5.၆၁ - 5.၅၁ (m, 1H), 4.၉၆ - 4.၈၉ (m, 2H), 3.၉၁ (t, J = ၇.၇ Hz, 2H), 2.၅၀ (s, 3H), 2.၃၆ (q, J = ၇.၄ Hz, 2H), 1.၈၉ (s, 3H).

[0114] 13 C NMR (101 MHz, CDCl3) δ 194.8, 146.1, 134.0, 133.8, 132.4, 132.3, 130.4, 129.6, 128.7, 127.1, 124.8, 122.6, 117.6, 115.8, 109.4, 43.6, 34.0, 30.1, 21.6.

[0115] The target product obtained in Example 8 is designated as Product 3h, and the yield is 51%. The structural formula is as follows:

[0116]

[0117] The characterization data of Product 3h are as follows:

[0118] 1 H NMR (400 MHz, CDCl3) δ 8.00 (d, J = 7.9 Hz, 1H), 7.54 - 7.45 (m, 4H), 7.34 (d, J = 7.9 Hz, 1H), 7.30 - 7.24 (m, 6H + overlapped with CDCl3), 7.12 (t, J = 7.6 Hz, 2H), 5.61 - 5.51 (m, 1H), 4.96 - 4.91 (m, 2H), 4.18 - 4.14 (m, 2H), 2.41 (q, J = 7.4 Hz, 2H).

[0119] 13 C NMR (101 MHz, CDCl3) δ 193.0, 146.1, 140.1, 136.2, 133.7, 130.9, 130.9, 130.9, 129.2, 128.7, 128.0, 127.8, 127.5, 123.2, 122.2, 122.0, 117.6, 115.1, 110.2, 43.6, 33.9.

[0120] The target product obtained in Example 9 is designated as Product 3i, and the yield is 58%. The structural formula is as follows:

[0121]

[0122] The characterization data of Product 3i are as follows:

[0123] 11H NMR (400 MHz, CDCl3) δ δ 8.53 - 8.48 (m, 1H), 7.38 - 7.30 (m, 7H), 5.65 - 5.54 (m, 1H), 5.00 - 4.93 (m, 2H), 3.98 - 3.94 (m, 2H), 2.48 (s, 3H), 2.43 - 2.36 (m, 2H), 1.94 (s, 3H).

[0124] 13 13C NMR (101 MHz, CDCl3) δ 194.9, 146.4, 139.8, 135.7, 133.9, 130.2, 129.5, 129.0, 126.9, 123.2, 122.9, 122.7, 117.6, 116.2, 109.7, 43.5, 34.1, 30.2, 21.5.

[0125] The target product obtained in Example 10 was designated as Product 3j, with a yield of 64%, and its structural formula is as follows:

[0126]

[0127] The characterization data of Product 3j are as follows:

[0128] 1 1H NMR (400 MHz, CDCl3) δ 8.48 - 8.44 (m, 1H), 7.71 - 7.68 (m, 2H), 7.40 - 7.22 (m, 5H), 5.63 - 5.53 (m, 1H), 5.01 - 4.92 (m, 2H), 3.98 - 3.95 (m, 2H), 2.43 - 2.37 (m, 2H), 2.00 (s, 3H).

[0129] 13 13C NMR (101 MHz, CDCl3) δ 194.6, 144.2, 133.6, 132.1, 132.0, 126.7, 124.2, 123.5, 122.9 (2C), 117.9, 116.4, 109.9, 43.6, 34.0, 30.4.

[0130] Experimental studies have shown that when the chemical structural formula of Substrate 1 in Example 1 is replaced with:

[0131]

[0132] When R 1 = COOH or NO2 or SO3H, R 2 = Boc or acetyl or Cbz, R 3When R is = COOH or NO2, according to the reaction conditions of Example 1, the reaction cannot proceed and the yield of the product is 0. Boc represents tert-butoxycarbonyl, acetyl represents acetyl, and Cbz represents benzyloxycarbonyl.

[0133] Experimental studies have shown that when the chemical structural formula of Substrate 2 in Example 1 is replaced with:

[0134]

[0135] When R 4 is = COOH or NO2 or SO3H, according to the reaction conditions of Example 1, the reaction cannot proceed and the yield of the product is 0.

[0136] Inspired by the ideal embodiments of the present invention described above, through the above description, relevant staff can make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst, characterized in that, Using indole compounds and diaryliodonium salt compounds as starting reaction materials, a blue light irradiation reaction is carried out at room temperature in a reaction solvent. After the reaction is completed, 2-arylindole compounds are obtained. The chemical structural general formula of the 2-arylindole compounds is represented as follows: In the above general chemical structure formula, R 1 is a substituent at any position on the benzene ring, and R 1 is selected from one of hydrogen, alkyl, alkoxy, halogen, and cyano; R 2 is alkyl; R 3 is selected from one of acetyl and benzoyl; R 4 is a substituent at any position on the benzene ring, and R 4 is selected from one of hydrogen, alkyl, and halogen.

2. A green method for the catalyst-free photo-driven synthesis of 2-arylindole compounds according to claim 1, characterized in that, The structural general formula of the indole compounds is represented as follows: In the above general formula of chemical structure, R 1 is at any position on the benzene ring, and R 1 is selected from one of hydrogen, alkyl, alkoxy, halogen, and cyano; R 2 is alkyl; R 3 is one of acetyl and benzoyl.

3. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst, characterized in that, The structural general formula of the diaryliodonium salt compounds is represented as follows: R 4 The substituent is at any position on the benzene ring, R 4 is selected from one of hydrogen, alkyl, and halogen.

4. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst according to claim 3, characterized in that, The diaryliodonium salt compounds are diaryliodonium trifluoromethanesulfonates.

5. A green method for the catalyst-free photocatalytic synthesis of 2-arylindole compounds according to claim 1, characterized in that, The reaction solvent includes one or more of 1,4-dioxane, tetrahydrofuran, acetonitrile, and 1,2-dichloroethane.

6. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst according to claim 1, characterized in that, The wavelength of the blue light irradiation is 456 nm.

7. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst according to claim 1, characterized in that, The time of the blue light irradiation reaction is 10 - 12 h.

8. A green method for the catalyst-free photo-driven synthesis of 2-arylindole compounds according to claim 1, characterized in that, The molar ratio of the indole compounds to the diaryliodonium salt compounds is 2:

3.

9. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst, characterized in that, The power of the blue light irradiation is 6 W, and the vertical distance between the light source and the upper surface of the reaction solvent is 5 - 10 cm.

10. A green method for the photocatalytic synthesis of 2-arylindole compounds without a catalyst according to claim 1, characterized in that, The dosage ratio of the indole compounds, the diaryliodonium salt compounds, and the reaction solvent is 0.2 mmol:0.3 mmol:2 mL.

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