Preparation method of bridged dithiopyrano [2, 3-b] indole compound

Abstract

The invention relates to the field of organic chemical synthesis, in particular to a preparation method of a bridged dithiopyrano [2, 3-b] indole compound. According to the method, the bridged bis-thiopyrano [2, 3-b] indole compound is simply and efficiently synthesized by taking indoline-2-thioketone and chromone 3-formaldehyde as initial raw materials and sodium bicarbonate and zinc chloride for concerted catalysis and taking dichloromethane as a solvent under the condition of heating reaction at 60 DEG C. The invention further discloses a preparation method of the bridged bis-thiopyrano [2, 3-b] indole compound. According to the method, the bridged bis-thiopyrano [2, 3-b] indole compound can be simply and efficiently prepared, raw materials are easy to obtain, operation is simple, Bronsted alkali and lewis acid are used for synergistic catalysis, the yield is excellent, inert gas protection is not needed in the preparation process, and the reaction condition is mild.

Description

Technical Field

[0001] The present invention relates to the field of organic chemical synthesis, and specifically to a preparation method of bridged bisthiopyrano[2,3-b]indole compounds. Background Art

[0002] As an important aromatic heterocyclic compound, indole's unique chemical properties and structure make it widely present in natural products and bioactive molecules. The indole skeleton occupies a core position in medicinal chemistry, and many drugs with antibacterial, anti-tumor, anti-inflammatory, and antiviral activities are based on the indole structure. However, a simple indole molecule has problems such as insufficient activity or low selectivity in some applications. To solve this problem, scientists have been committed to modifying the indole structure, and introducing sulfur-containing heterocycles has become an important strategy.

[0003] Due to their unique electronic effects, steric effects, and special interactions with biological targets, sulfur-containing heterocycles can effectively improve the pharmacological activities and physicochemical properties of indole compounds. The high polarizability and multiple valence states of sulfur atoms enable them to regulate the electronic distribution of molecules when combined with indole, enhancing their binding ability with biological macromolecules. In addition, the introduction of sulfur-containing heterocycles can also improve the metabolic stability and liposolubility of compounds, thereby improving pharmacokinetic properties. Such structural modifications not only expand the research field of indole chemistry but also provide important theoretical guidance and practical value for the development of new drugs and functional materials. Summary of the Invention

[0004] The present invention provides a synthesis method of bridged bisthiopyrano[2,3-b]indole compounds. This method realizes the simple and efficient synthesis of bridged bisthiopyrano[2,3-b]indole compounds under the conditions of using indoline-2-thione and chromone 3-carbaldehyde as starting materials, synergistically catalyzed by sodium bicarbonate and zinc chloride, using dichloromethane as a solvent, and heating the reaction at 60°C.

[0005] The technical solution of the present invention is specifically as follows:

[0006] A preparation method of bridged bisthiopyrano[2,3-b]indole compounds, and the structural formula III of the bridged bisthiopyrano[2,3-b]indole compounds is shown as follows:

[0007]

[0008] Wherein, R 1 is a substituent at different positions on the indole benzene ring, including methoxy, chlorine-based electron-withdrawing or electron-donating substituents, and R 2 is a different substitution on the indole N, including methyl or hydrogen-based substituents. R 3They are substituents at different positions on the chromone benzene ring, including methoxy, fluorine, chlorine or phenyl substituents, and are characterized in that the preparation method is as follows:

[0009]

[0010] The preparation steps of the target compound III include: dissolving compound I and compound II in dichloromethane, adding zinc chloride and sodium bicarbonate and stirring for reaction. After monitoring the reaction of compound I by thin layer chromatography and stopping the reaction, the reaction mixture is removed of the solvent under reduced pressure, and the target compound III is obtained by elution with silica gel column chromatography.

[0011] As a further improvement of the preparation method, the replacement of the dichloromethane solvent includes: 1,2-dichloroethane, chloroform, ethyl acetate, methanol, acetonitrile or tetrahydrofuran.

[0012] As a further improvement of the preparation method, the replacements of zinc chloride include: scandium trifluoromethanesulfonate, tin trifluoromethanesulfonate, indium trifluoromethanesulfonate, zinc trifluoromethanesulfonate, aluminum chloride or magnesium iodide.

[0013] As a further improvement of the preparation method, the replacements of sodium bicarbonate include: sodium carbonate, potassium carbonate, sodium methoxide, triethylamine, or DABCO.

[0014] As a further improvement of the preparation method, the molar ratio of compound I to compound II is I∶II = 2:1.

[0015] As a further improvement of the preparation method, the eluent used in the silica gel column chromatography is a mixed solvent of petroleum ether and dichloromethane, and the volume ratio V 石油醚 :V 二氯甲烷 = 5:1 to 1:3.

[0016] As a further improvement of the preparation method, the reaction temperature for preparing the target compound III is 25°C to 80°C.

[0017] As a further improvement of the preparation method, the reaction temperature for preparing the target compound III is 60°C.

[0018] The beneficial effects brought by the technical solutions provided in the embodiments of this application at least include the following

[0019] Beneficial effects:

[0020] The present invention uses indoline-2-thione and chromone-3-carbaldehyde as reactants, and uses zinc chloride and sodium bicarbonate for synergistic catalysis to simply and efficiently prepare bridged bisthiopyrano[2,3-b]indole compounds, and there is no need for inert gas protection during the preparation process, and the reaction conditions are mild. Description of the Drawings

[0021] Figure 11H NMR spectrum of Product Ⅲ-1 obtained in the embodiments of the present invention

[0022] Figure 2 13C NMR spectrum of Product Ⅲ-1 obtained in the embodiments of the present invention Detailed implementation manners

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0024] Example 1 The reaction formula of Example 1. The specific compounds I-1, II-1 and the structure of Product Ⅲ-1 used are as follows. Experiments show that the best organic solvent used in the present invention is dichloromethane, the highest yield of its reaction product is 98%, the best molar ratio of raw materials is Compound I-1:Compound II-1 = 2:1, and the best reaction concentration is 0.1M.

[0025]

[0026] The specific experimental procedure is as follows: Dissolve 65 mg (0.4 mmol, 2.0 equivalents) of Compound I-1 and 35 mg (0.2 mmol, 1.0 equivalent) of Compound II-1 in 2 mL of dichloromethane, add 3 mg of zinc chloride (0.02 mmol, 0.1 equivalent), 17 mg of sodium bicarbonate (0.2 mmol, 1.0 equivalent), and stir and react at 60 °C. Stop the reaction after monitoring the reaction of reactant I-1 by thin-layer chromatography. Rotate and evaporate the solvent dichloromethane from the reaction mixture under reduced pressure with a water pump. The residue is subjected to column chromatography on silica gel with 200-300 mesh, and the eluent (volume ratio V 石油醚 :V 二氯甲烷 = 5:1 to 1:1) to obtain 94 mg of the compound shown as Ⅲ-1. The product is identified by nuclear magnetic resonance (1H NMR, 13C NMR) and high-resolution mass spectrometry.

[0027] Product Ⅲ-1 is a yellow solid, with a yield of 98% and a melting point of 208-210 °C. 11H NMR (500 MHz, CDCl3) δ 11.64 (s, 1H), 7.81 (dd, J = 8.2, 1.6 Hz, 1H), 7.70 - 7.66 (m, 1H), 7.57 - 7.50 (m, 2H), 7.21 - 7.12 (m, 6H), 7.08 (d, J = 8.4 Hz, 1H), 6.92 (t, J = 7.6 Hz, 1H), 5.32 (d, J = 3.8 Hz, 1H), 5.22 (d, J = 1.4 Hz, 1H), 4.72 (dd, J = 3.9, 1.6 Hz, 1H), 3.50 (s, 3H), 3.43 (s, 3H). 13 13C NMR (125 MHz, CDCl3) δ 202.1, 162.7, 137.8, 137.6, 136.6, 133.1, 130.0, 129.3, 126.4, 126.2, 121.2, 121.1, 119.8, 119.6, 119.3, 118.1, 117.3, 116.9, 108.7, 107.6, 106.5, 48.0, 38.8, 35.2, 30.3, 30.1, (2C is merged with other peaks); ESI - HRMS m / z calcd for C 28 H 23 N2O2S2 [M + H] + 483.1195, found 483.1194.

[0028] The methods used in the examples for preparing other compounds (Compound III - 2 to Compound III - 13) of the present invention are the same as those in Example 1, and the reaction conditions are as follows: Compound I (0.4 mmol) and Compound II (0.2 mmol) are dissolved in 2 mL of dichloromethane, 3 mg of zinc chloride (0.02 mmol, 0.1 equivalent) and 17 mg of sodium bicarbonate (0.2 mmol, 1.0 equivalent) are added, and the reaction is stirred at 60 °C. The reaction is stopped after monitoring the completion of the reaction of Reactant I by thin - layer chromatography. The reaction mixture is rotary - evaporated under reduced pressure with a water pump to remove the solvent dichloromethane. The residue is subjected to column chromatography on silica gel with 200 - 300 mesh, and the eluent (volume ratio V 石油醚 :V 二氯甲烷 = 5:1 to 1:2) to obtain the compound shown in III.

[0029] The structures and data characterizations of the obtained products are as follows:

[0030]

[0031] Product III - 2 is a yellow solid, with a yield of 99%, melting point: 205 - 207 °C. 1HNMR(500MHz,CDCl3)δ11.68(s,1H),7.87(d,J=7.41Hz,1H),7.53(td,J=8.6,7.2,1.6Hz,1H),7.12-6.99(m,7H),6.95(t,J=7.6Hz,1H),5.95(d,J=3.5Hz,1H),5.80(s,1H),4.77(dd,J=3.3,1.7Hz,1H),3.51(s,3H),3.45(s,3H); 13 C NMR(125MHz,CDCl3)δ202.0,162.9,139.2,139.0,136.8,134.3,131.2,129.2,124.3,124.2,123.3,123.2,121.5,121.4,121.0,120.8,119.5,119.4,117.9,108.5,107.5,107.3,107.3,47.4,38.6,35.2,30.7,30.5;ESI-HRMS m / z calcd forC 28 H 21 Cl2N2O2S2[M+H] + 551.0416,found 551.0418.

[0032] The product Ⅲ-3 is a yellow solid with a yield of 97%, melting point: 188 - 190 °C. 1 H NMR(500MHz,CDCl3)δ11.64(s,1H),7.82(d,J=7.6Hz,1H),7.53(t,J=7.4Hz,1H),7.14(d,J=2.4Hz,1H),7.08(d,J=8.3Hz,1H),7.04(t,J=8.4Hz,2H),6.99(d,J=2.4Hz,1H),6.93(t,J=7.5Hz,1H),6.82-6.76(m,2H),5.26(d,J=3.8Hz,1H),5.16(s,1H),4.71(dd,J=3.9,1.7Hz,1H),3.93(s,3H),3.88(s,3H),3.46(s,3H),3.39(s,3H); 13CNMR(125MHz, CDCl3) δ 202.1, 162.7, 154.4, 154.3, 136.6, 133.4, 133.0, 133.0, 130.4, 129.4, 126.8, 126.7, 119.4, 118.2, 110.4, 110.3, 109.4, 107.2, 106.0, 100.4, 99.8, 56.2, 56.1, 48.2, 39.0, 35.3, 30.6, 30.4, (2C is merged with other peaks); ESI-HRMS m / z calcd for C 30 H 27 N2O4S2 [M+H] + 543.1407, found 543.1409.

[0033] Product Ⅲ-4 is a yellow solid, yield 80%, melting point: 218 - 220 °C. 1 H NMR(500MHz, CDCl3) δ 11.53(s, 1H), 7.79(dd, J = 8.2, 1.6Hz, 1H), 7.61(d, J = 1.8Hz, 1H), 7.57 - 7.53(m, 1H), 7.48 - 7.46(m, 1H), 7.12 - 7.05(m, 5H), 6.99 - 6.94(m, 1H), 5.23(d, J = 3.9Hz, 1H), 5.13(d, J = 1.5Hz, 1H), 4.69(dd, J = 3.9, 1.6Hz, 1H), 3.49(s, 3H), 3.43(s, 3H); 13 C NMR(125MHz, CDCl3) δ 201.7, 162.8, 136.9, 136.3, 136.1, 134.7, 131.7, 129.2, 127.3, 127.2, 125.9, 125.7, 121.4, 121.3, 119.5, 119.5, 118.0, 117.0, 116.6, 109.7, 109.7, 107.2, 106.2, 47.9, 38.7, 35.0, 30.7, 30.5; ESI-HRMS m / z calcd for C 28 H 21 Cl2N2O2S2 [M+H] + 551.0416, found 551.0417.

[0034] Product Ⅲ-5 is a yellow solid, yield 93%, melting point: 193 - 195 °C. 11H NMR (500 MHz, CDCl3) δ 11.55 (s, 1H), 7.80 (d, J = 8.0 Hz, 1H), 7.57 - 7.52 (m, 2H), 7.41 (d, J = 8.4 Hz, 1H), 7.19 - 7.15 (m, 2H), 7.15 - 7.09 (m, 2H), 7.07 (d, J = 8.4 Hz, 1H), 6.95 (t, J = 7.6 Hz, 1H), 5.25 (d, J = 3.8 Hz, 1H), 5.15 (d, J = 1.5 Hz, 1H), 4.69 (dd, J = 3.9, 1.6 Hz, 1H), 3.46 (s, 3H), 3.40 (s, 3H); 13 13C NMR (125 MHz, CDCl3) δ 201.7, 162.8, 138.2, 138.1, 136.9, 133.8, 130.8, 129.2, 127.4, 127.4, 124.9, 124.8, 120.5, 120.3, 119.5, 118.0, 117.7, 109.0, 109.0, 107.8, 106.7, 47.8, 38.6, 35.0, 30.6, 30.4, (2C is merged with other peaks); ESI - HRMS m / z calcd for C 28 H 21 Cl2N2O2S2 [M + H] + 551.0416, found 551.0417.

[0035] The product Ⅲ - 6 is a yellow solid, with a yield of 95%, melting point: 193 - 195 °C. 1 1H NMR (500 MHz, CDCl3) δ 11.56 (s, 1H), 7.78 (dd, J = 8.2, 1.7 Hz, 1H), 7.56 - 7.50 (m, 2H), 7.38 (dd, J = 7.8, 1.2 Hz, 1H), 7.09 - 7.03 (m, 4H), 7.00 (t, J = 7.8 Hz, 1H), 6.95 - 6.91 (m, 1H), 5.24 (d, J = 3.8 Hz, 1H), 5.14 (d, J = 1.6 Hz, 1H), 4.69 (dd, J = 3.9, 1.6 Hz, 1H), 3.87 (s, 3H), 3.81 (s, 3H); 1313C NMR (125 MHz, CDCl3) δ 201.7, 162.8, 136.9, 135.3, 133.2, 133.1, 132.3, 129.3, 129.2, 129.2, 123.1, 123.1, 120.7, 120.6, 119.5, 119.5, 118.0, 116.6, 116.5, 116.0, 115.6, 107.9, 106.8, 47.8, 38.7, 35.0, 33.8, 33.6; ESI-HRMS m / z calcd for C 28 H 21 Cl2N2O2S2 [M+H] + 551.0416, found 551.0416.

[0036] Product Ⅲ-7 is a yellow solid, yield 85%, melting point: 210 - 212 °C. 1 1H NMR (500 MHz, (CD3)2SO) δ 11.08 (s, 1H), 10.89 (s, 1H), 10.83 (s, 1H), 7.67 (dd, J = 7.9, 1.8 Hz, 1H), 7.65 - 7.62 (m, 1H), 7.52 (d, J = 7.3 Hz, 1H), 7.50 - 7.46 (m, 1H), 7.17 - 7.14 (m, 2H), 7.03 - 6.93 (m, 6H), 5.29 (d, J = 1.6 Hz, 1H), 5.22 (d, J = 3.8 Hz, 1H), 4.81 (dd, J = 3.8, 1.7 Hz, 1H); 13 13C NMR (125 MHz, (CD3)2SO)) δ 198.6, 157.2, 136.6, 136.2, 134.4, 131.0, 129.9, 127.3, 126.6, 126.2, 122.9, 120.6, 120.4, 119.6, 118.9, 118.7, 117.3, 117.2, 117.1, 110.3, 110.2, 108.6, 107.2, 50.8, 36.5, 33.8; ESI-HRMS m / z calcd for C 26 H 18 N2O2S2Na [M+Na] + 477.0702, found 477.0704.

[0037] Product Ⅲ-8 is a yellow solid, yield 98%, melting point: 213 - 215 °C. 11H NMR (500 MHz, CDCl3) δ 11.70 (s, 1H), 7.69 - 7.64 (m, 1H), 7.54 - 7.50 (m, 1H), 7.41 (t, J = 8.4 Hz, 1H), 7.19 - 7.09 (m, 6H), 6.67 (d, J = 8.3 Hz, 1H), 6.47 (d, J = 8.2 Hz, 1H), 5.30 (d, J = 1.3 Hz, 1H), 5.23 (d, J = 3.6 Hz, 1H), 4.98 (dd, J = 3.7, 1.6 Hz, 1H), 3.79 (s, 3H), 3.49 (s, 3H), 3.40 (s, 3H); 13 13C NMR (125 MHz, CDCl3) δ 202.4, 164.0, 159.9, 137.9, 137.6, 136.0, 133.1, 130.8, 126.5, 120.9, 120.8, 119.6, 119.5, 117.3, 116.9, 111.6, 110.7, 108.6, 108.6, 108.4, 106.8, 101.9, 56.2, 52.8, 37.3, 35.2, 30.4, 30.2, (1C is merged with other peaks); ESI-HRMS m / z calcd for C 29 H 25 N2O3S2 [M + H] + 513.1301, found 513.1301.

[0038] Product Ⅲ-9 is a yellow solid, with a yield of 97%, melting point: 204 - 206 °C. 1 1H NMR (500 MHz, CDCl3) δ 11.74 (s, 1H), 7.74 (d, J = 8.7 Hz, 1H), 7.68 - 7.64 (m, 1H), 7.57 - 7.50 (m, 1H), 7.21 - 7.11 (m, 6H), 7.08 (d, J = 2.1 Hz, 1H), 6.91 (dd, J = 8.5, 2.1 Hz, 1H), 5.25 (d, J = 3.8 Hz, 1H), 5.19 (d, J = 1.7 Hz, 1H), 4.64 (dd, J = 4.0, 1.8 Hz, 1H), 3.50 (s, 3H), 3.44 (s, 3H); 13CNMR(125MHz,CDCl3)δ201.4,163.4,142.5,137.8,137.7,133.1,130.3,129.9,126.3,126.2,121.3,121.2,120.1,119.9,119.7,119.4,117.3,116.9,116.8,108.8,108.8,107.4,106.4,48.3,38.8,35.1,30.5,30.3;ESI-HRMS m / z calcd for C 28 H 22 ClN2O2S2[M+H] + 517.0806,found 517.0807.

[0039] Product Ⅲ-10 is a yellow solid, with a yield of 98%, melting point: 200 - 202 °C. 1 H NMR(500MHz,CDCl3)δ11.34(s,1H),7.66(dd,J=7.8,2.0Hz,1H),7.55(dd,J=5.8,2.3Hz,1H),7.48(dd,J=8.6,2.7Hz,1H),7.32 - 7.27(m,1H),7.21 - 7.12(m,6H),7.04(dd,J=9.2,4.5Hz,1H),5.30(d,J=3.9Hz,1H)5.20(s,1H),4.62(dd,J=3.9,1.7Hz,1H),3.51(s,3H),3.44(s,3H); 13 C NMR(125MHz,CDCl3)δ201.3(d,J=2.6Hz),159.0,155.1(d,J=238.5Hz),137.8,137.7,133.1,129.9,126.4,126.2,124.4(d,J=23.4Hz),121.3,121.2,120.8(d,J=7.4Hz),119.9,119.7,117.7(d,J=6.0Hz),117.4,117.0,114.3(d,J=23.2Hz),108.8,108.8,107.4,106.3,48.3,38.6,35.1,30.5,30.3; 19 F NMR(376MHz,CDCl3)δ - 122.8(m,1F);ESI-HRMS m / z calcd for C 28 H 22 FN2O2S2[M+H] + 501.1101,found 501.1101.

[0040] Product Ⅲ-11 is a yellow solid with a yield of 88% and a melting point of 199-201 °C. 1 H NMR (500 MHz, CDCl3) δ 13.41 (s, 1H), 8.48 (d, J = 8.4 Hz, 1H), 7.79 (d, J = 8.1 Hz, 1H), 7.72 (d, J = 8.9 Hz, 1H), 7.70 - 7.64 (m, 2H), 7.58 - 7.51 (m, 2H), 7.30 (d, J = 8.9 Hz, 1H), 7.21 - 7.11 (m, 6H), 5.39 (d, J = 3.8 Hz, 1H), 5.27 (d, J = 1.6 Hz, 1H), 4.79 (dd, J = 3.9, 1.6 Hz, 1H), 3.51 (s, 3H), 3.44 (s, 3H); 13 C NMR (125 MHz, CDCl3) δ 201.8, 163.1, 137.7, 137.6, 137.2, 133.1, 130.4, 130.2, 127.5, 126.3, 126.3, 126.2, 125.6, 124.7, 123.5, 121.1, 121.0, 119.7, 119.6, 118.8, 117.3, 116.9, 111.5, 108.6, 108.6, 107.7, 106.5, 48.1, 38.5, 35.2, 30.4, 30.2; ESI-HRMS m / z calcd for C 32 H 25 N2O2S2 [M + H] + 533.1352, found 533.1353.

[0041] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and without departing from the spirit or basic characteristics of the present invention, the present invention can be implemented in other specific forms. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention.

[0042] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a bridged dithiopyrano[2,3-b]indole compound. The structural formula III of the bridged dithiopyrano[2,3-b]indole compound is as follows: in, R 1 are substituents at different positions on the indole benzene ring, including methoxy, chlorine-type electron-withdrawing or electron-donating substituents, R 2 is a different substitution on the indole N, including a methyl or hydrogen substituent; R 3 The chromone is a substituent at different positions on the benzene ring, including a methoxy, fluorine, chlorine or phenyl substituent, characterized in that the preparation method is as follows: The preparation steps of the target compound III include: dissolving compound I and compound II in dichloromethane, adding zinc chloride and sodium bicarbonate and stirring the reaction, stopping the reaction after the reaction of compound I is completed by thin layer monitoring, removing the solvent from the reaction mixture under reduced pressure, and eluting by silica gel column chromatography to obtain the target compound III.

2. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to claim 1, characterized in that: The dichloromethane solvent replacement includes: 1,2-dichloroethane, chloroform, ethyl acetate, methanol, acetonitrile or tetrahydrofuran.

3. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to claim 1, characterized in that: The zinc chloride substitutes include scandium trifluoromethanesulfonate, tin trifluoromethanesulfonate, indium trifluoromethanesulfonate, zinc trifluoromethanesulfonate, aluminum chloride or magnesium iodide.

4. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to claim 1, characterized in that: The sodium bicarbonate substitutes include: sodium carbonate, potassium carbonate, sodium methoxide, triethylamine, or DABCO.

5. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to claim 1, characterized in that: The molar ratio of the compound I to the compound II is I:II=2:

1.

6. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to claim 1, characterized in that: The eluent used for the silica gel column chromatography is a mixed solvent of petroleum ether and dichloromethane, and the volume ratio is V 石油醚 :V 二氯甲烷 =5:1~1:

3.

7. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to any one of claims 1 to 6, characterized in that: The reaction temperature for preparing the target compound III is 25°C to 80°C.

8. The method for preparing a bridged dithiopyrano[2,3-b]indole compound according to claim 7, characterized in that: The reaction temperature for preparing the target compound III is 60°C.

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