General procedure for the synthesis of 6-bromo-3-chloroisoquinoline from 6-bromo-1,3-dichloroisoquinoline: a mixture of 6-bromo-1,3-dichloroisoquinoline (1.8 g, 6.5 mmol), red phosphorus (0.48 g, 15.5 mmol), and hydriodic acid (3 ml, 48%) in acetic acid (20 ml) was heated and refluxed for 8 hours. After completion of the reaction, it was filtered while hot and the filtrate was concentrated under reduced pressure. The concentrated residue was alkalized by addition of sodium hydroxide solution and subsequently extracted with ethyl acetate (200 mL). The organic phase was washed with saturated saline, dried over anhydrous magnesium sulfate, filtered and concentrated. The concentrate was purified by silica gel fast column chromatography to afford 6-bromo-3-chloroisoquinoline (0.81 g, 50% yield) using 30% ethyl acetate/hexane as eluent. Mass spectrum (DCI/NH3) m/e 244 (M+H)+.
