Dimethyl Sulfide → 3-Bromo-6-fluoro-2-hydroxybenzaldehyde

Ozone was conducted into a solution of 8.0 g (35 mmol) of 7-bromo-4-fluoro-2-methylbenzofuran at -78° C. until the colour became blue. Subsequently, argon was conducted through the solution which was then treated at -78° C. with 13 ml of dimethyl sulfide. After warming to room temperature the solution was concentrated in a vacuum and the residue was dissolved in 50 ml of ethanol. After the addition of 50 ml of 3% sodium hydrogen carbonate solution the mixture was stirred at 70° for 30 minutes. Subsequently, the mixture was poured on to 200 ml of ice-water, made acid with 10% HCl and extracted three times with 150 ml of diethyl ether. After drying over sodium sulfate concentration was carried out in a vacuum. The crude product obtained was purified by column chromatography on silica gel (dichloromethane/hexane 4:1). There were obtained 7.5 g (98%) of 3-bromo-6-fluoro-2-hydroxy-benzaldehyde as a pale yellow oil, which was used immediately in the next reaction.