Methyl 3-((tert-butoxycarbonyl)amino)thiophene-2-carboxylate → 3-[(tert-Butoxycarbonyl)amino]thiophene-2-carboxylic acid

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Methyl 3-t-butoxycarbonylaminothiophene-2-carboxylate (15.0 g, 58.3 mmol) was warmed in a mixture of 1 N sodium hydroxide (116.6 ml) and tetrahydrofuran (60 ml) at 50° C. for 16 hours. The mixture was evaporated to a volume of approximately 60 ml, and acidified (pH=2) with hydrochloric acid under cooling in an ice bath. The precipitate was filtered off, washed with water, and dried to afford 13.8 g (97%) of 3-t-butoxycarbonylaminothiophene-2-carboxylic acid. M.p. 168°-169° C. Litt. m.p. 168-169° C. (i. Chem. Res. (S) , 296, 1985). 1H-NMR (DMSO-D6, δ) : 1.49 (s, 9H), 7.76 (d, 1H), 7.85 (d, 1H), 9.45 (s, 1H), 13.45 (s, 1H) .

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