Vinylmagnesium bromide (300 mL of a 1.0 M THF solution, 300 mmol) was slowly added dropwise to a solution of 4-bromo-1-fluoro-2-nitrobenzene (22 g, 100 mmol) in anhydrous THF (700 mL) at -40 °C. The reaction temperature was maintained at -40 °C and after 1 h, the reaction was quenched with saturated aqueous NH4Cl solution. Subsequently, the reaction mixture was extracted with EtOAc (ethyl acetate). The organic layers were combined, dried with anhydrous Na2SO4, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography, eluting with appropriate proportions of eluents to afford the target compound 4-bromo-7-fluoro-1H-indole (5 g, 23.3% yield). The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz): δ 6.56-6.58 (m, 1H), 6.72-6.79 (m, 1H), 7.06-7.17 (m, 1H), 7.20-7.24 (m, 1H), 8.45 (s, 1H).
