Borane-tetrahydrofuran complex (16.21 mL, 1 M) was slowly added dropwise to a solution of tetrahydrofuran (10 mL) containing 2-fluoro-4-nitrobenzoic acid (1.2 g) at 0 °C. The reaction mixture was maintained at 80°C for 3 hours. Upon completion of the reaction, it was cooled to room temperature and acidified by addition of 1N aqueous hydrochloric acid solution (20 mL), followed by extraction with ethyl acetate. The organic phase was washed sequentially with saturated aqueous sodium bicarbonate, dried over anhydrous sodium sulfate and concentrated under reduced pressure to give (2-fluoro-4-nitrophenyl)methanol (0.91 g, 83% yield) as an oil. The resulting (2-fluoro-4-nitrophenyl)methanol (0.91 g) was mixed with manganese dioxide (1.1 g) in dichloromethane (20 mL) and stirred overnight at room temperature. The reaction mixture was filtered through diatomaceous earth and the filtrate was concentrated under reduced pressure to give 2-fluoro-4-nitrobenzaldehyde (0.27 g, 30% yield) as an oil.
