GENERAL METHOD: To a solution of 5-bromoindole (6.8 mmol) in anhydrous acetonitrile (6.0 mL) was slowly added chlorosulfonyl isocyanate (CSI) (0.63 mL, 7.25 mmol) dropwise at 0 °C, and the reaction mixture was kept stirring at 0 °C for 2 hours. Subsequently, anhydrous dimethylformamide (DMF) (1.3 mL, 170.0 mmol) was added dropwise and stirring was continued at 0 °C for 2 hours. Upon completion of the reaction, the mixture was poured into water and the resulting precipitate was collected by filtration. The precipitate was dried over anhydrous Na2SO4 and purified by column chromatography with the eluent being petroleum ether/ethyl acetate (40/60) or pure ethyl acetate to afford the target product 5-bromo-3-cyanoindole.
