Dimethylformamide → 2,4-Difluoro-3-methylbenzaldehyde

A cooled (−78° C.) solution of 2,4-difluoro-3-methylbromobenzene (2.000 g; 9.661 mmol) in anhydrous THF (36 ml) was treated dropwise (over 10 min.) with a solution of 1.6M n-BuLi in hexanes (6.04 ml; 9.661 mmol) while maintaining the temperature below −70° C. This mixture was further stirred at −78° C. for 2 min. before anhydrous DMF (1.49 ml; 19.326 mmol) was added dropwise (over 10 min.) while maintaining the temperature below −70° C. After completion of the addition, the resulting light brown solution was further stirred at −78° C. for 1 h30. The resulting mixture was then quenched at −78° C. with aq. sat. NH4Cl (10 ml), and was then allowed to warm-up to rt. Ether (50 ml) and water (20 ml) were added, and the organic layer was dried over anh. MgSO4, filtered, and concentrated to dryness under reduced pressure (caution: rotary evaporation bath at 30° C. because the aldehyde is volatile). The crude was purified by FC (DCM) to give the pure product 2,4-difluoro-3-methyl-benzaldehyde as a pale yellow oil (1.250 g; 83%).