4-Fluoro-2-methyl-5-phthalimidoindole (1.2 g, 4 mmol) was used as starting material and dissolved in methanol (30 mL). Hydrazine monohydrate (260 μL, 5.3 mmol) was added to the solution and the reaction mixture was stirred for 2 h at room temperature. After completion of the reaction, the solvent was removed by rotary evaporation. The residue was dissolved in dichloromethane and filtered to remove the resulting phthalic hydrazide by-product. The filtrate was purified by fast column chromatography using a dichloromethane solution containing 0.5% methanol as eluent. The solvent in the eluate was evaporated to give a white solid containing traces of phthalic hydrazide. For further purification, the solid was dissolved in ethyl acetate and the organic phase was washed sequentially with 2N NaOH solution and brine, and then dried with anhydrous magnesium sulfate. Finally, the solvent was removed by rotary evaporation to afford 5-amino-4-fluoro-2-methylindole (500 mg, 76% yield). The product was confirmed by 1H NMR (DMSO-d6): δ 2.35 (s, 3H), 4.30 (s, 2H), 5.95 (s, 1H), 6.55 (t, 1H), 6.85 (d, 1H), 10.70 (br s, 1H). Mass spectrometry (ESI) showed the molecular ion peak m/z 165 [M+H]+.
