6-METHYLINDOLE-3-CARBOXALDEHYDE

1. Synthesis of indole derivatives; 1) Synthesis of 3-cyanoindole derivatives; Nine objective compounds were prepared by (1) formylation of 3-position of the corresponding indole using phosphorus oxychloride in the presence of dimethylformamide (Vilsmeier method), (2) cyanation by dehydrating reaction with hydroxylamine in sodium formate and formic acid, (3) coupling with ethyl 4-fluorobenzoate in the presence of potassium fluoride on almina and 18-crown-6-ether in dimethyl sulfoxide and then, (4) hydrolysis with lithium hydroxide in total 4 steps in that order (the following Table 2). In addition, XO-CH172 and XO-CH183 (R is a 2-methyl group or a 5-methoxy group, respectively) were prepared from the step (2) using the corresponding aldehydes purchased.; 1) Synthesis of XO-CH200; XO-CH180 Under an argon atmosphere, 6-methylindole (1.004 g, 7. 62 mmol) was dissolved in dimethylformamide (10 mL), and to the solution was added phosphorus oxychloride (2 mL) under ice-cooling. The mixture was stirred for 1.5 hours at room temperature. To the reaction mixture was added dropwise an aqueous sodium hydroxide solution (5g/15mL) under ice-cooling. The mixture was heated for reflux for 1.5 hours. To the reaction mixture was added water under ice-cooling, and the mixture was adjusted to pH3 with concentrated hydrochloric acid. The solid was collected by filtration and dried at 60°C under reduced pressure to give XO-CH180 as a pale brown solid (1.14 g, 94percent yield).General procedure: The Vilsmeier-Haack reagent was prepared by adding POClGeneral procedure: A 50 mL round bottom flask equipped with a magnetic stirring bar was charged with substituted indole 1 (1.0 mmol, 1.0 equiv), HMTA (2.0 mmol, 0.2803 g, 2.0 equiv), activated carbon (0.1 g) and DMF (2 mL). Then IGeneral procedure: A 50 mL round-bottomed flask equipped with a magnetic stirringbar was charged with the appropriate indole 1 (0.5 mmol, 1.0 equiv), 37percent aq HCHO (0.5 mmol, 0.0406 g, 1.0 equiv), 25percent aqNH3 (1.0 mmol, 0.0681 g, 2.0 equiv), FeCl3 (0.01 mmol, 0.0016 g, 2 molpercent), and DMF (2 mL). The flask was fitted with a reflux condenser, and the mixture was stirred at 130 °C under open air.When the reaction was complete (TLC), the mixture was cooledto r.t., diluted with sat. aq NaCl (10 mL) and 0.5 M aq HCl (2 mL), and extracted with EtOAc (3 x 7 mL). The organic layers werecombined, washed with sat. aq NaHCO3 (10 mL) and sat. aq NaCl(10 mL), dried (Na2SO4), and concentrated under reduced pressure.The residue was purified by flash column chromatography(silica gel, hexane–EtOAc).1. Synthesis of indole derivatives; 1) Synthesis of 3-cyanoindole derivatives; [Show Image] Nine objective compounds were prepared by (1) formylation of 3-position of the corresponding indole using phosphorus oxychloride in the presence of dimethylformamide (Vilsmeier method), (2) cyanation by dehydrating reaction with hydroxylamine in sodium formate and formic acid, (3) coupling with ethyl 4-fluorobenzoate in the presence of potassium fluoride on almina and 18-crown-6-ether in dimethyl sulfoxide and then, (4) hydrolysis with lithium hydroxide in total 4 steps in that order (the following Table 2). In addition, XO-CH172 and XO-CH183 (R is a 2-methyl group or a 5-methoxy group, respectively) were prepared from the step (2) using the corresponding aldehydes purchased.; 1) Synthesis of XO-CH200; XO-CH180 Under an argon atmosphere, 6-methylindole (1.004 g, 7. 62 mmol) was dissolved in dimethylformamide (10 mL), and to the solution was added phosphorus oxychloride (2 mL) under ice-cooling. The mixture was stirred for 1.5 hours at room temperature. To the reaction mixture was added dropwise an aqueous sodium hydroxide solution (5g/15mL) under ice-cooling. The mixture was heated for reflux for 1.5 hours. To the reaction mixture was added water under ice-cooling, and the mixture was adjusted to pH3 with concentrated hydrochloric acid. The solid was collected by filtration and dried at 60C under reduced pressure to give XO-CH180 as a pale brown solid (1.14 g, 94% yield).Add 30 mL of N, N-dimethylformamide (DMF) to a 250 mL three-necked flask, cool to below 0 C, and slowly add phosphorus oxychloride (6.30 mL, 67 mmol). After the addition is complete, let stand at room temperature and continue to stir. After 30 min, 25 mL of 6-methyl-1H-indole (II-3, 8.00 g, 61 mmol) in DMF was added dropwise in an ice bath. The temperature was controlled below 10 C. After the addition was completed, the temperature was raised to 35 C and stirred for 1 h.The reaction was monitored by TLC. After the reaction was completed, the reaction was quenched by adding 60 g of crushed ice under ice cooling, and then slowly added dropwise.1mol/L NaOH solution, adjust pH=89, and control the temperature in the dropping process to not exceed 40C. After the addition is completed, the mixture is heated to reflux for 1 hour.Stirring was carried out, cooled to room temperature, 55 mL of water was added dropwise, filtered, and the filter cake was washed with water until neutral. After drying, 8.67 g of a yellow solid was obtained.III-3, 89.38%.General procedure: The Vilsmeier-Haack reagent was prepared by adding POCl3 (60 mmol, 6 mL) dropwise to ice-cold dry DMF (30 mL) whilst stirring. The mixture was then stirred for 10-15 min at 0 C. Compound 3b or 3e (10 mmol) was added as a solution in DMF (5 mL) to the above Vilsmeier-Haack reagent. The stirred mixture was then heated at 35 C for 1 h. After cooling, ice water (6 mL) and a 30% aqueous solution of NaOH (13 mL) were added successively, and the mixture was heated at reflux for 20 min and allowed to cool. The mixture was extracted with CH2Cl2 (20 mL*3). The extracts were dried over Na2SO4, evaporated under reduced pressure to remove the solvent, and the crude product was purified by flash column chromatography using 15-25% acetone/petroleum ether (60-90 C) as eluent to give the corresponding intermediate compound 4b or 4e, respectively.6-Methyl indole-3-carboxaldehyde Phosphorus oxychoride (3.2 ml, 34.3 mmol) was added dropwise to dimethyl formamide (26 ml) over ten minutes at ~5 C. To this solution was added a dimethyl formamide (32 ml) solution of 6-methylindole (3.307 g, 25.2 mmol) over 10 minutes. The mixture was slowly warmed to ambient temperature, then heated to 50 C. for four hours. The mixture was cooled to ambient temperature, then poured onto ice (500 g). The aqueous solution was left to stand for 16 hours. Sodium hydroxide (6.0 g) was dissolved in water (22 ml) and added dropwise to the brown solution. The resultant yellow precipitate was boiled and filtered hot. It was left to cool to room temperature, then to 5 C. The precipitate was filtered off and washed with water (800 ml), dried at the pump, then further dried in vacuo at 50 C. for 16 hours to yield a yellow solid.General procedure: A method for synthesizing compound III-1 wherein R1, R2 and R3 are simultaneously hydrogen in the formula III, the method comprising the steps of:(1) Add to a 50 mL round bottom flask1.0mmol indole(In the formula I, R1, R2, and R3 are both hydrogen) and1.0 mmol (0.140 g) of hexamethylenetetramine, then 2 mL of N, N-dimethylformamide (DMF), stirred in a magnetic stirrer to dissolve the solid, followed by the addition of 0.05 mmol (0.012 g) of crystalline trichloride Aluminum, connected to a reflux condenser, heated at 120 ° C, the reaction progress was monitored by TLC, and the reaction was cooled to room temperature after 1 h to prepare a suspension;(2) The suspension prepared in the step (1) is suction filtered with a funnel padded with diatomaceous earth.The filter cake was washed well with ethyl acetate, suction filtered, and the above operation was repeated until the filtrate had no product, and all the filtrates were combined.Dilute with 15 mL of saturated saline solution, disperse and separate the layers, and the aqueous layer was further extracted with ethyl acetate three times.Each time 10 mL, the ethyl acetate layer was combined and washed with 10 mL of 2 mol/L diluted hydrochloric acid.Wash with 10 mL of saturated sodium bicarbonate solution, and finally wash with 10 mL of saturated brine.The washed ethyl acetate layer was dried over anhydrous sodium sulfate, and after drying, the desiccant was filtered off.Then use a rotary evaporator to recover the solvent to concentrate the product, and finally, The residue is subjected to silica gel column chromatography using a mixture of n-hexane-ethyl acetate (V/V = 2:1) as an eluent to obtain a purified product.The mass of the compound III-indole-3-carbaldehyde is 0.137g, The product yield was 94percent.General procedure: A mixture of compound 1 (500 mg, 2.72 mmol), piperidine (0.027 mL) and glacial acetic acid (0.10 mL) was stirred in toluene (30 mL) at 45 C for 0.5 h, then 6-chloro-1H-indole-3-carbaldehyde (486 mg, 2.72 mmol) was added. Upon completion of the reaction, the mixture was evaporated under reduced pressure and cooled to room temperature, the residue was extracted with chloroform (3 * 20 mL), and the combined organic phase was dried over anhydrous sodium sulfate and further purified by silica gel column chromatography (eluent, chlorlform/acetone, 8/1, V/V) to give compound 2b (657.23 mg) as yellow solid.