General procedure for the synthesis of 3-fluoro-4-bromobenzaldehyde from 4-bromo-3-fluorobenzyl alcohol: Manganese dioxide (18.7 g, 210 mmol) was added to a solution of 4-bromo-3-fluorobenzyl alcohol (4.3 g, 21 mmol) in chloroform (50 mL), and the reaction mixture was stirred at 37 °C overnight. The progress of the reaction was monitored by thin layer chromatography (TLC) until the raw material was completely consumed. Upon completion of the reaction, the mixture was filtered and the filtrate was concentrated under reduced pressure to afford the target product 3-fluoro-4-bromobenzaldehyde (2.3 g, 55% yield).
