General procedure for the synthesis of 3-bromo-5-chloro-1H-indazole from 5-chloro-1H-indazole: 5-chloro-1H-indazole (2.5 g, 16.1 mmol) was dissolved in dichloromethane (150 mL) and N-bromosuccinimide (2.9 g, 16.6 mmol) was added. The reaction mixture was stirred at room temperature for 1 hour. Upon completion of the reaction, the solvent was removed by concentration under reduced pressure and the residue was dissolved in ethyl acetate (100 mL) and washed sequentially with water (50 mL) and saturated saline (50 mL). The organic phase was dried with anhydrous sodium sulfate, filtered and concentrated under reduced pressure to afford 3-bromo-5-chloro-1H-indazole (3.7 g, 94% yield) as a brown solid. The product was confirmed by 1H NMR (DMSO-d6, 400MHz): δ 13.63 (s, 1H), 7.67-7.59 (m, 2H), 7.49-7.44 (m, 1H).TLC analytical conditions: 50% ethyl acetate/heptane (Rf = 0.43).
