General procedure: To a solution of 1-chloro-6-methoxyisoquinoline (1.93 g, 10 mmol) in anhydrous dichloromethane (30 mL) was added boron tribromide (30 mL, 30 mmol) slowly and dropwise at -78 °C. The reaction was carried out at room temperature with continuous stirring for 16 hours. The reaction system was gradually warmed to room temperature and stirred continuously for 16 hours. Upon completion of the reaction, the mixture was recooled to -78 °C and the reaction was quenched with methanol (1 mL). The solvent was removed by concentration under reduced pressure and the residue was washed twice with water to afford 1.4 g of the target product 1-chloro-6-hydroxyisoquinoline as a white solid. The structure of the product was confirmed by 1H NMR (400 MHz, CDCl3): δ 8.26 (d, J = 9.0 Hz, 1H), 8.16 (d, J = 5.6 Hz, 1H), 7.43 (d, J = 5.9 Hz, 1H), 7.27 (d, J = 2.4 Hz, 1H), 7.12 (d, J = 2.2 Hz, 1H).
