To a solution of tert-butyl 4-bromo-3-methylphenyl(5-cyano-6-methoxypyridin-2-yl)carbamate (2.85 g, 6.81 mmol) in carbon tetrachloride (50 mL) was added N-bromosuccinimide (0.909 g, 5.11 mmol) and azobisisobutyronitrile (0.042 g, 0.26 mmol). The mixture was refluxed under nitrogen at 95° C. for two hours. The reaction was cooled to room temperature, water was added and the mixture was extracted with dichloromethane. The organic layer was washed with water and brine, and dried on anhydrous sodium sulfate. The solvent was removed under reduced pressure to give crude tert-butyl 4-bromo-3-(bromomethyl)phenyl(5-cyano-6-methoxypyridin-2-yl)carbamate (4.12 g). The product was used in the next step without further purification.
