Dimethyl Sulfate → 1-Methylindole-3-carboxylic acid

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A cooled (0° C.) suspension of 60% sodium hydride-oil dispersion (0.96 g, 24 mmol) in anhydrous N,N-dimethylformamide (15 mL) under nitrogen was treated in portions with indole-3-carboxylic acid (1.62 g, 10 mmol), and the mixture was stirred at 45°±5° C. for 30 minutes. Dimethylsulfate (3.03 g, 24 mmol) was added, and the mixture was heated to 100° C. for 30 minutes, cooled, and added to ice water (100 mL). The suspension was filtered and the wet solid was washed with water and taken up in 50% aqueous methanol (40 mL). The mixture was treated with 50% aqueous sodium hydroxide (3.0 g, 37.5 mmol) and refluxed for 30 minutes, then the methanol was removed in vacuo and replaced with water. The aqueous solution was extracted with ether (50 mL), then acidified with 3N HCl to pH 3 (15 mL). The suspension was filtered and the solid was washed with water and dried exhaustively m vacuo in the presence of Drierite. Recrystallization from acetonitrile afforded 1.32 g (75%) of colorless crystals; mp 201°-202° C. (dec).

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