Step B: Synthesis of 2,6-difluoro-4-methylbenzaldehyde
To a solution of 1,3-difluoro-5-methylbenzene (10.2 g, 80 mmol) in anhydrous ether (80 mL), n-butyllithium (2.5 M hexane solution, 48 mL, 120 mmol) was slowly added at -50 °C, and the addition time was controlled to be within 20 minutes. The reaction temperature was maintained at -50 °C and stirring was continued for 1.5 hours. Subsequently, N,N-dimethylformamide (14.6 g, 200 mmol) was added dropwise over 20 min at the same temperature. After the dropwise addition, the temperature was kept constant and stirring was continued for 1.5 hours. After completion of the reaction, the reaction mixture was slowly poured into 1N aqueous sulfuric acid solution (300 mL) and extracted with ether three times. The organic layers were combined, washed with saturated brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure to afford the target product 2,6-difluoro-4-methylbenzaldehyde (11.2 g, 90% yield).
1H-NMR (500 MHz, CDCl3): δ 10.25 (s, 1H), 6.75 (d, 2H, J = 9.9Hz), 2.39 (s, 3H).
