General procedure for the synthesis of 7-bromo-5-nitro-1H-indole from 7-bromo-5-nitroindole: 7-bromo-5-nitroindole (3 g, 12.34 mmol) was dissolved in ethanol (30 mL), DDQ (5.6 g, 24.69 mmol) and isopropanol (2 mL) were added. The reaction mixture was stirred at 80 °C for 48 hours. Upon completion of the reaction, the reaction mixture was concentrated under reduced pressure and the residue was partitioned between ethyl acetate and water. The organic layer was separated, washed with water, dried over anhydrous sodium sulfate, filtered and the filtrate concentrated under reduced pressure. The crude product was purified by fast chromatography using a hexane solution of 20% ethyl acetate as eluent to give the title compound (2.5 g, 84%) as a yellow solid.1H NMR (300 MHz, DMSO-d6): δ 12.13 (bs, 1H), 8.62 (d, J=1.8 Hz, 1H), 8.18 (d, J=1.8 Hz, 1H) , 7.67 (t, J=3.0Hz, 1H), 6.89 (m, 1H).ESI-MS m/z=241 (M+H)+.
