Citric Acid → 4-Methyl-7-[(2-thienylsulfonyl)amino]-1H-indole-2-carboxylic acid

Participants

Reaction Steps

To a mixed solution of ethyl-4-methyl-7-[(2-thienylsulfonyl)amino]-1H-indole-2-carboxylate (0.88 g) in tetrahydrofuran (20 mL)-methanol (10 mL) was added aqueous solution (5 mL) of 85% potassium hydroxide (0.56 g), and the mixture was stirred at room temperature for 15 hr. Aqueous citric acid solution was added to the reaction mixture, and the mixture was extracted with ethyl acetate, washed with saturated brine, dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The obtained crystals were washed with ethyl acetate-hexane to give the title compound (777 mg, yield 96%) as colorless crystals. melting point>280° C. (decomposition).

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