The general procedure for the synthesis of 4-fluoro-5-hydroxy-2-methylindole from 2-acetylmethylene-3-fluoro-4-benzyloxynitrobenzene was as follows: 3-acetylmethyl-1-benzyloxy-2-fluoro-4-nitrobenzene (300 mg, 0.99 mmol) was dissolved in ethanol (10 mL) and acetic acid (1 mL) containing 10% palladium charcoal (30 mg), and the reaction was carried out at 50 °C in a 2 atmosphere of hydrogen at 2 atmospheres for 2 hours. Upon completion of the reaction, the mixture was filtered to remove the catalyst and the filtrate was subsequently evaporated to remove the solvent. The residue was dissolved in ethyl acetate and the organic phase was washed sequentially with aqueous sodium bicarbonate and saturated saline, followed by evaporation of the solvent to afford the crude product 4-fluoro-5-hydroxy-2-methylindole. The crude product was purified by column chromatography using ethyl acetate/petroleum ether (3:7, v/v) as eluent to finally obtain purified 4-fluoro-5-hydroxy-2-methylindole (63 mg, 30% yield). Mass spectrum (MS-ESI): m/z 166 [M+H]+. 1H NMR (DMSO-d6, δ): 2.35 (s, 3H), 6.05 (s, 1H), 6.65 (dd, 1H), 6.9 (d, 1H), 8.75 (s, 1H), 10.9 (s, 1H). 13C NMR (DMSO-d6, δ). 94.0, 106.0, 112.0, 118.5 (d), 132.0 (d), 136.0 (d), 136.5, 142.5 (d).
