GENERAL STEPS: (2-Amino-4-nitrophenyl)methanol (650 mg, 3.87 mmol) was reacted with manganese dioxide (1680 mg, 19.33 mmol) in a solvent mixture of tetrahydrofuran (5 mL) and dichloromethane (25 mL) with stirring for 2 hours at room temperature. Upon completion of the reaction, the reaction mixture was filtered to remove insoluble solids and the filtrate was subsequently concentrated. The resulting crude product was purified by silica gel column chromatography (eluent: 40%-50% hexane solution of ethyl acetate; silica gel column: 25 g) to afford the target compound 2-amino-4-nitrobenzaldehyde (550 mg, 86% yield) as an orange solid. Its 1H NMR (400 MHz, DMSO-d6) data were as follows: δ 9.99 (s, 1H), 7.85 (d, J = 8.6 Hz, 1H), 7.63 (d, J = 2.3 Hz, 1H), 7.55 (br.s., 2H), 7.35 (dd, J = 8.6, 2.3 Hz, 1H).
