4-Bromo-1H-indole-7-carboxylic acid (5.5 g, 22.91 mmol) was used as a starting material and dissolved with EDC (6.59 g, 34.4 mmol) and HOBt (5.26 g, 34.4 mmol) in a solvent mixture of THF (150 mL) and DCM (180 mL). The reaction mixture was stirred at room temperature for 1 h to activate the carboxyl groups. Subsequently, NH3 gas was passed into the reaction system for about 15 minutes and stirring was continued overnight at room temperature to complete the amidation reaction. Upon completion of the reaction, the reaction mixture was diluted by addition of water and extracted with DCM. The organic phases were combined, washed with brine, dried over anhydrous sodium sulfate and concentrated to give the crude product. The crude product was suspended in ether and filtered to give 4-bromo-1H-indole-7-carboxamide (5.3 g, 97% yield) as a white solid. The structure of the product was confirmed by 1H NMR (DMSO-d6): δ 11.40 (br, 1H), 8.08 (br, 1H), 7.29-7.57 (d, J = 7.6 Hz, 1H), 7.43-7.42 (m, 2H), 7.28-7.26 (d, J = 7.6 Hz, 1H), 6.43-6.42 (m, 1H).
