Boron tribromide → 2-Chloro-6-hydroxyquinoline-3-carbaldehyde

To a −78° C. mixture of 2-chloro-6-methoxyquinoline-3-carbaldehyde (4.64 g, 20.9 mmol) in dichloromethane (130 mL) was added boron tribromide (4.0 mL, 42 mmol). The mixture was allowed to warm to room temperature and stir for 4 hours. The reaction was neutralized by the careful addition of saturated aqueous sodium bicarbonate. The mixture was then extracted with 2-methyl tetrahydrofuran (3×). The combined organics were filtered, and the filtrate was washed with saturated aqueous sodium bicarbonate (3×) and once with brine. The organics were dried over sodium sulfate, filtered, and concentrated to a yellow solid. The solid was partially dissolved in 2-methyl tetrahydrofuran and filtered. The filtrate was concentrated to a solid and again partially dissolved in 2-methyl tetrahydrofuran, filtered, and concentrated. Purification by flash column chromatography (10-100% ethyl acetate/heptanes) gave the title compound (2.65 g, 61%) as a pale yellow solid. +ESI (M+H) 208.1; 1H NMR (400 MHz, CDCl3, δ): 10.54 (s, 1 H), 8.59 (s, 1 H), 7.98 (d, J=9.17 Hz, 1 H), 7.47 (dd, J=9.17, 2.73 Hz, 1 H), 7.25 (d, J=2.93 Hz, 1 H), 5.57 (br. s., 1 H).