General procedure for the synthesis of 3-fluoro-4-nitrobenzaldehyde from 3-fluoro-N-methoxy-N-methyl-4-nitrobenzamide: 3-fluoro-N-methoxy-N-methyl-4-nitrobenzamide was added to 800 mL of tetrahydrofuran (THF) under ice-salt/water bath cooling conditions. Subsequently, a THF solution of 1 M diisobutylaluminum hydride (DIBAL) was slowly added through the addition funnel over 30 min. The reaction mixture was stirred under nitrogen (N2) protection for 1 hour. Upon completion of the reaction, the reaction mixture was carefully diluted with 1N hydrochloric acid (500 mL) and ethyl acetate (EtOAc, 500 mL) and then transferred to a separatory funnel for separation. The organic phase was washed sequentially with 1N hydrochloric acid (3 × 250 mL), 1N sodium hydroxide (2 × 250 mL) and water (250 mL). All aqueous layers were back-extracted with ethyl acetate (2 × 250 mL). The organic layers were combined, dried with anhydrous magnesium sulfate (MgSO4), filtered and concentrated in vacuum to give 67 g of the target product 3-fluoro-4-nitrobenzaldehyde (396 mmol, 88% yield). The product was confirmed by nuclear magnetic resonance hydrogen spectroscopy (1H-NMR, DMSO-d6): δ 10.06 (s, 1H), 8.36-8.32 (t, J = 7.8 Hz, 1H), 8.06-8.03 (d, J = 11.2 Hz, 1H), 7.95-7.93 (d, J = 9.1 Hz, 1H).
