General procedure for the synthesis of 5-bromo-2-difluoromethylpyridine from 5-bromo-2-pyridinecarboxaldehyde: To a cooled solution of 5-bromopyridine-2-carboxaldehyde (A) (7.0 g, 38 mmol) in dichloromethane (300 mL) was slowly added diethylaminosulfur trifluoride (DAST, 10.8 mL, 83 mmol) at -78 °C. The reaction mixture was gradually warmed to room temperature over a period of 6 h. The reaction was subsequently quenched by the slow addition of water. The reaction mixture was washed with saturated aqueous sodium bicarbonate solution and dried with anhydrous sodium sulfate. Concentration and purification by silica gel column chromatography (dichloromethane as eluent) afforded 5-bromo-2-difluoromethylpyridine (B) as brown crystals (5.3 g, 67% yield).1H NMR (300 MHz, CDCl3) δ 8.8 (s, 1H), 8.0 (d, 1H), 7.6 (d, 1H), 6.6 (t, 1H).
