General procedure for the synthesis of 2-bromo-4,5-difluorobenzaldehyde from (2-bromo-4,5-difluorophenyl)methanol: (2-bromo-4,5-difluorophenyl)methanol (1.23 g, 5.50 mmol), triethylamine (1.39 g, 13.75 mmol) and dimethylsulfoxide (1.72 g, 22.00 mmol) were dissolved in dichloromethane (25 mL) in dichloromethane (25 mL) and cooled to 0°C. Subsequently, sulfur trioxide-pyridine complex (1.32 g, 8.25 mmol) was added in batches. The reaction mixture was stirred at 0 °C for 1 h. Triethylamine (1.39 g, 13.75 mmol), dimethyl sulfoxide (1.72 g, 22.00 mmol) and sulfur trioxide-pyridine complex (1.32 g, 8.25 mmol) were added again. After continued stirring at 0 °C for 30 min, the reaction solution was diluted with dichloromethane (50 mL) and washed sequentially with saturated sodium bicarbonate solution and saturated sodium thiosulfate solution. The organic phase was dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. Purification by fast column chromatography (RediSep fast column, 230-400 mesh silica gel, eluent 10-30% ethyl acetate in hexane solution) afforded 2-bromo-4,5-difluorobenzaldehyde (0.47 g, 39% yield).1H NMR (300 MHz, CDCl3) δ 10.23 (s, 1H), 7.77 (m, 1H), 7.52 (m, 1H).
