Sodium Hydroxide → 2-(4-methylphenyl)-7,8-dihydro-6H-cyclohepta[b]thiophene-5-carboxylic acid

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To a solution of methyl 2-(4-methylphenyl)-7,8-dihydro-6H-cyclohepta[b]thiophene-5-carboxylate (803 mg) in ethanol-tetrahydrofuran (5-10 ml) was added 2N sodium hydroxide (2 ml) at room temperature, and the mixture was stirred for 5 days and concentrated under reduced pressure. To the residue was added 1N hydrochloric acid (10 ml), and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated sodium chloride solution, dried with magnesium sulfate and concentrated under reduced pressure to precipitate crystals, which were collected by filtration and washed with diisopropylether to give 2-(4-methylphenyl)-7,8-dihydro-6H-cyclohepta[b]thiophene-5-carboxylic acid (650 mg) as pale yellow crystals.

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