Dimethylformamide → 4-Bromo-2,5-difluorobenzaldehyde

To a solution of 2,5-dibromo-1,4-difluorobenzene (10.0 g, 36.77 mmol) in diethyl ether (150 mL) at −78° C. was added n-butyl lithium (2.5 M in Hexanes, 14.86 mL, 37.15 mmol) dropwise under nitrogen. The reaction mixture was stirred at −78° C. for 30 min. Dry DMF (3.13 mL, 40.46 mmol) in diethyl ether (10 mL) was added dropwise and reaction was slowly warmed to room temperature over 2 h. The reaction was quenched with aqueous saturated ammonium chloride solution (25 mL) and extracted with diethyl ether. The organic phase was washed with saturated brine solution, dried (Na2SO4), filtered, and concentrated under reduced pressure (Note: Product is highly volatile). The crude product was purified by flash chromatography (SiO2, eluting with 2-20% ethyl acetate in hexanes) to provide the title compound as a pale yellow solid (7.0 g, 86%): 1H NMR (400 MHz, CDCl3): δ 7.50 (dd, J=5.08, 8.92 Hz, 1H), 7.62 (dd, J=5.80, 7.68 Hz, 1H), 10.30 (d, J=2.76 Hz, 1H).