To a solution of o-vanillin (11; 4.0 g, 0.026 mol) in acetic acid (80 mL) was added sodium acetate (2.37 g, 0.029 mol) at 0 °C, followed by slow dropwise addition of bromine (1.49 mL, 0.029 mol). The reaction mixture was stirred at room temperature for 30 min. After completion of the reaction, water (100 mL) was added and the aqueous phase was extracted with dichloromethane (3 x 80 mL). The organic phases were combined, washed sequentially with water (100 mL) and brine (50 mL), dried over anhydrous magnesium sulfate, and concentrated under reduced pressure to remove the solvent. The crude product was purified by fast column chromatography (petroleum ether:ethyl acetate = 19:1) to afford 5-bromo-2-hydroxy-3-methoxybenzaldehyde (26; 6.0 g, 98%) as a yellow solid with a melting point of 119-123 °C (literature value 19: 122-124 °C).1H NMR (400 MHz, CDCl3/TMS): δ = 3.92 (3H, s, OCH3), 7.18 (1H, d, J = 2.4 Hz, 4-H), 7.31 (1H, d, J = 2.4 Hz, 6-H), 9.86 (1H, s, CHO), 11.00 (1H, s, OH).13C NMR (100 MHz, CDCl3): δ = 56.3 (OCH3), 111.1 (C-5), 120.8 (C-6), 121.3 (C-1), 126.1 (C-4), 149.3 (C-2), 150.9 (C-3), 195.4 (CHO).The 1H NMR and 13C NMR data are in agreement with the literature values19.
