Synthesis
Starting with substituted trifluoromethylbenzaldehyde, 5-(TRIFLUOROMETHYL)ISATIN was prepared via a cyclization reaction after the preparation of a key intermediate, hydroxylamine. The reaction formula is shown in the figure below: [Image of 345-32-4 synthesis] Sodium methoxide (28% methanol solution, 87 ml) cooled to -8°C was slowly added dropwise to 200 ml of methanol solution with stirring. After stirring at the same temperature for 2 hours, the reaction solution was poured into ice water, the precipitated crystals were collected by filtration, washed with water, and dried to obtain the azide. A solution of 14.4 g of the obtained azide in 120 mL of xylene was slowly added dropwise to 300 mL of boiling xylene. The mixture was then refluxed for 1 hour, cooled, and the precipitated crystals were collected by filtration and dried to obtain methyl 5-trifluoromethyl-indole-2-carboxylic acid. (mp 182-183 °C) To a methanol solution of methyl 5-trifluoromethyl-indole-2-carboxylic acid, 35 mL of 2N sodium hydroxide was added, and the mixture was heated under reflux for 2 hours. Next, methanol was distilled off under reduced pressure, and the residue was diluted with water and acidified with hydrochloric acid. The precipitated crystals were collected by filtration, washed with water, and dried to give 7.9 g of 5,7-difluoro-5-trifluoromethyl-indole-2-carboxylic acid. Under ice-cooled conditions, 5.6 g of ethyl N,N-dichlorocarbamate was added to an aqueous solution of 4.0 g of 5-trifluoromethyl-indole-2-carboxylic acid in acetic acid (84 ml acetic acid - 21 ml water). The mixture was stirred for 1 hour. Water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure, and the residue was dissolved in 60 ml of 50% methanol aqueous solution, heated to reflux for 1 hour, and stirred overnight at room temperature. Methanol was removed by distillation under reduced pressure, and water was added to the residue. The residue was extracted with ethyl acetate, and the organic layer was washed with saturated brine and dried over anhydrous magnesium sulfate. The solvent was concentrated under reduced pressure, and the residue was purified by silica gel column chromatography and recrystallized from ethyl acetate-n-hexane to give the title compound 5-(TRIFLUOROMETHYL)ISATIN.
