General procedure for the synthesis of 4-bromo-3-chloro-N-methoxy-N-methylbenzamide as raw material for 4-bromo-3-chlorobenzaldehyde: 4-bromo-3-chloro-N-methoxy-N-methylbenzamide (1.80 g, 6.46 mmol) was dissolved in anhydrous tetrahydrofuran (32 mL) in a 10 mL single-necked round-bottomed flask under argon protection. The reaction system was cooled to -78 °C and 1M diisobutylaluminum hydride solution (8.4 mL, 8.40 mmol) was slowly added dropwise. The reaction temperature was maintained at -78 °C and the reaction mixture was stirred for 1 hour. Upon completion of the reaction, the reaction was quenched with 50 mL of water, followed by extraction of the aqueous layer with ethyl acetate (3 x 50 mL). The organic layers were combined and washed sequentially with 1N hydrochloric acid solution (30 mL), water (30 mL) and brine (30 mL). The organic layer was dried over anhydrous magnesium sulfate and concentrated under reduced pressure. The resulting product was dried under high vacuum to give a yellow solid 4-bromo-3-chlorobenzaldehyde (1.18 g, 84% yield). The structure of the product was confirmed by 1H NMR (300 MHz, DMSO-d6): δ 9.98 (s, 1H), 8.11 (d, 1H, J = 1.9 Hz), 8.02 (AB system, 1H, J = 8.2 Hz), 7.77 (dd, 1H, J = 1.9 Hz, 8.2 Hz).
