Vinylmagnesium bromide (177 mL of 1.0 M THF solution, 0.177 mol) was added slowly and dropwise to a solution of 4-bromo-1-chloro-2-nitrobenzene (14 g, 0.059 mol) dissolved in 400 mL of THF at -40 °C. The reaction mixture was stirred continuously at -40°C for 2 hours. Upon completion of the reaction, the reaction was quenched by the addition of aqueous NH4Cl, followed by extraction with ether. The organic phases were combined, dried with anhydrous Na2SO4 and concentrated under reduced pressure to remove the solvent. The crude product was purified by silica gel column chromatography to afford the target compound 7-chloro-4-bromoindole (6 g, 44% yield).1H NMR (CDCl3, 400 MHz) δ: 8.5 (s, 1H), 7.31-7.29 (m, 1H), 7.26-7.22 (m, 1H), 7.07-7.05 (m, 1H), 6.65-6.63 ( m, 1H).
