Methanol → 2-Tert-butoxycarbonyl-1,2,3,4-tetrahydro-benzo[b]thieno[2,3-c]pyridine-3-carboxylic acid

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In a mixed solvent of 30 ml of methanol and 20 ml of chloroform was dissolved 6 g of 2-tert-butoxycarbonyl-1,2,3,4-tetrahydrobenzo[b]thieno[2,3-c]pyridine-carboxylic acid ethyl ester and 4 ml of an aqueous solution of 5N sodium hydroxide was further added thereto, and then the solution was refluxed for 5 hours. The solvents were distilled off under reduced pressure and 300 ml of 5% citric acid and 300 ml of chloroform were added to the residue. The chloroform layer was washed with a saturated aqueous sodium chloride solution and then dried by sodium sulfate. After distilling off chloroform under reduced pressure, the residue formed was recrystallized from a mixture of chloroform and hexane to provide 4.15 g (yield of 75%) of 2-tert-butoxycarbonyl-1,2,3,4-tetrahydrobenzo[b]thieno[2,3-c]pyridine-3-carboxylic acid.

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