General procedure for the synthesis of 2,4-difluoro-5-bromonitrobenzene from 2,4-difluorobromobenzene: Concentrated HNO3 (34.0 mL) was added slowly and dropwise to a suspension of 1-bromo-2,4-difluorobenzene (53.0 mmol, 6.00 mL) in concentrated H2SO4 (38.5 mL) at 0 °C, ensuring that the internal temperature was maintained below 0 °C. The reaction mixture was stirred for 10 minutes with vigorous stirring. The reaction mixture was continued to be stirred at 0 °C for 10 min and subsequently poured into an ice/water mixture under vigorous stirring. The mixture was extracted with ether (ET20, 3 x 100 mL). The combined organic phases were washed sequentially with aqueous NaHCO3 (3 x 100 mL) and brine, dried over MgSO4, filtered and concentrated under reduced pressure. The crude product was purified by fast chromatography (eluent: EtOAc/hexane=1:9) to afford 5-bromo-2,4-difluoronitrobenzene as a yellow oil (12.2 g, 97% yield).1H NMR (400 MHz, CDCl3) δ 8.45 (t, 1H, J=7.5 Hz), 7.16 (dd, 1H, J=11.0,8.6 Hz) ; ESMS m/z: 240, 238, 223, 221, 112.
