a) General procedure for the synthesis of 2,3-difluoro-6-methoxybenzaldehyde: A 2 M solution of diisopropylaminolithium THF/n-heptane (171 mL, 341 mmol) was diluted with dry THF (250 mL) under nitrogen protection and cooled to -75°C. A solution of 3,4-difluoroanisole (46.8 g, 325 mmol) in anhydrous THF (100 mL) was added slowly dropwise and stirred for 1 hour keeping the temperature at -75 °C. Subsequently, dry N,N-dimethylformamide (27.6 mL, 358 mmol) was added slowly and stirring was continued at -70 °C for 10 min. After the reaction was completed, acetic acid (30 mL) and water (400 mL) were added and warmed to 10 °C. The reaction mixture was extracted with ether (2 x 300 mL). The organic phases were combined and washed sequentially with water (250 mL), 0.2N aqueous hydrochloric acid (400 mL) and brine (2 x 250 mL), dried with anhydrous magnesium sulfate, and the solvent was concentrated under reduced pressure to give a red to orange oil, which was allowed to stand and crystallized. Purification by recrystallization from ether/petroleum ether (40-60 °C) afforded the target product 2,3-difluoro-6-methoxybenzaldehyde (53.0 g, 95% yield).1H NMR (300 MHz, CDCl3) δ: 10.40 (1H, s, CHO), 7.37 (1H, q, ArH), 6.71 (1H, m, ArH), 3.93 ( 3H, s, OCH3).
