Methyl 1H-indole-6-carboxylate (1.00 g, 5.71 mmol) was dissolved in anhydrous DMF (10 mL) under nitrogen atmosphere. A solution of N-bromosuccinimide (NBS, 1.04 g, 5.84 mmol) in anhydrous DMF (10 mL) was added slowly dropwise at -60 °C over 20 min. The reaction mixture was stirred at -60 °C, followed by a slow warming to room temperature over 3 hours. Upon completion of the reaction, it was extracted with ethyl acetate (100 mL) and water (20 mL, repeated three times). The organic layers were combined and the solvent was removed by vacuum concentration. The residue was purified by silica gel column chromatography with the eluents being petroleum ether and ethyl acetate (the proportion of ethyl acetate was increased in a gradient from 0%) to give methyl 3-bromoindole-6-carboxylate (1.41 g, 98% yield). The product was characterized by 1H NMR (600 MHz, CD3OD): δ 8.15 (s, 1H), 7.80 (d, J = 6.0 Hz, 1H), 7.50 (m, 2H), 3.94 (s, 3H).
