Step 3. Preparation of 2-bromo-6-(difluoromethyl)pyridine
To a solution of 6-bromopyridine-2-carbaldehyde (2.10 g, 11.29 mmol) in dichloromethane (20 mL) was slowly added diethylamino sulfur trifluoride (1.94 mL, 14.68 mmol) at 0 °C. The reaction mixture was gradually warmed to room temperature and stirred continuously for 18 hours. Upon completion of the reaction, the mixture was carefully poured into pre-cooled saturated sodium bicarbonate solution (300 mL). Extraction was carried out with ethyl acetate (2 x 120 mL) and the organic phases were combined. Subsequently, the organic phase was washed sequentially with saturated sodium bicarbonate solution (80 mL) and brine (2 x 50 mL), dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated under reduced pressure to afford 2-bromo-6-(difluoromethyl)pyridine as a brown oil (2.17 g, 89% yield). The product was characterized by 1H NMR (300 MHz, CDCl3): δ 7.75-7.70 (m, 1H), 7.65-7.60 (m, 2H), 6.60 (t, J = 55.1 Hz, 1H).
