5-Bromo-1H-indole-3-carboxylic acid

General procedure: In a dried two-necked test tube was charged with LiOtBu (160 mg, 2.00 mmol) and indole 1a (23.4 mg, 0.4 mmol). The reaction vessel was evacuated under high vacuum and the atmosphere was replace with a balloon of CO2. Then DMF (2 mL) was added and the mixture was stirred for 24 h at 100°C. Then the result mixture was cooled and carefully quenched with a solution of HCl (2 N) and extracted with EtOAc (5x). The combined organic layers were washed with water (2x), brine (1x) and dry over MgSO4. The dried organics were concentrated under reduce pressure and the residue was purified by preparative TLC (hexane:acetone = 1:1) to afford the desired product 2a (153.0 mg, 95percent) as a white solid.A flask was charged with 1-(5-bromo-1H-indol-3-yl)-2, 2, 2-trifluoroethanone (hb) (4.30 g, 14.72 mmol) and an aqueous solution of sodium hydroxide (180 mL, 20percent wt.) was added. This mixture was refluxed for 2h30 then carefully acidified to pH = 1 with an aqueous solution of 6M HCl. During this acidification, the carboxylic acid precipitated. The resulting suspension was filtered. The solid was washed with water and dissolved in a mixture of ethyl acetate/methanol (about 9/1). The organic layer was dried over anhydrous MgSOA flask was charged with 1-(5-bromo-lH-indol-3-yl)-2, 2, 2-trifluoroethanone (hb) (4.30 g, 14.72 mmol) and an aqueous solution of sodium hydroxide (180 mL, 20percent wt.) was added. This mixture was refluxed for 2h30 then carefully acidified to pH = 1 with an aqueous solution of 6M HCl. During this acidification, the carboxylic acid precipitated. The resulting suspension was filtered. The solid was washed with water and dissolved in a mixture of ethyl acetate/methanol (about 9/1). The organic layer was dried over anhydrous MgSO4 and evaporated under vacuum. The desired product (2b) (3.528 g, 14.7 mmol) was obtained as a beige solid. Yield: quant.1H NMR (300 MHz, DMSO-dGeneral procedure: 6 g of substituted indole-3-aldehydes (10a–b) was dissolved in 600 mL of acetone.To this KMnO