General procedure for the synthesis of 2-fluoro-5-nitrophenol from 2-fluoro-5-nitroanisole: 116 ml (116 mmol) of boron tribromide (1 M dichloromethane solution) was added slowly dropwise to 5.00 g (29.2 mmol) of 1-fluoro-2-methoxy-4-nitrobenzene solution over 1 h at -10 °C, and the rate of the dropwise acceleration was controlled so that the reaction temperature did not exceed -5 °C. After completion of the reaction, the reaction solution was stirred at 0°C for 5 hours. Subsequently, the reaction was quenched by slow addition of 600 ml of ice water and diluted with 100 ml of ethyl acetate. After separation of the organic phase, the aqueous phase was extracted twice with ethyl acetate. All organic phases were combined and dried with anhydrous sodium sulfate. After filtration, the solvent was removed by concentration under reduced pressure. The residue was purified by silica gel column chromatography (eluent ratio 10:1 cyclohexane/ethyl acetate) to afford 1.45 g (30% yield) of the target product 2-fluoro-5-nitrophenol. The structure of the product was confirmed by 1H NMR (400 MHz, DMSO-d6, δ/ppm): 10.99 (s, 1H), 7.78 (dd, 1H), 7.73 (ddd, 1H), 7.44 (dd, 1H).HPLC analysis (Method 1): retention time Rt = 3.60 min. Mass spectrum (DCI, m/z): 174 (M + NH4)+.
