General procedure for the synthesis of 3,4-difluoro-2-hydroxybenzaldehyde from 2-hydroxy-3,4-difluorobenzyl alcohol: To a stirred solution of 2-hydroxy-3,4-difluorobenzyl alcohol (2.5 g, 15.62 mmol) in dichloromethane (20 mL) was slowly added DDQ (5.32 g, 23.43 mmol) in dichloromethane (-5 to 0°C) ( 10mL) solution. The reaction mixture was then stirred overnight at room temperature. The progress of the reaction was monitored by thin layer chromatography (TLC) to confirm complete consumption of the raw materials. Upon completion of the reaction, the mixture was filtered through a bed of diatomaceous earth and the filtrate was concentrated under vacuum to obtain the crude product. The crude product was purified by silica gel column chromatography using pure dichloromethane as eluent to give the target product 3,4-difluoro-2-hydroxybenzaldehyde (2 g, 83% yield). Mass spectrometry (MS) analysis showed m/z 157 (M + 1).
