To a suspension of 4-fluoro-7-carboxyindole in a solvent mixture of methanol (18 mL) and benzene (62 mL), (trimethylmethylsilyl) diazomethane (8.8 mL, 17.6 mmol, 2 M hexane solution) was slowly added. The reaction mixture was stirred at room temperature for 30 min, followed by quenching the reaction with excess acetic acid. The reaction solution was concentrated in vacuum and the resulting crude product was purified by fast column chromatography using gradient elution (hexane to 10% ethyl acetate/hexane) as eluent to give the final methyl 4-fluoro-1H-indole-7-carboxylate as a white solid (1.04 g, 83% yield in two steps).
