Potassium Hydroxide → 4H,5H,6H-cyclopenta[c]thiophene-5-carboxylic acid

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Reaction Steps

Dissolve 5,5-(dicarboethoxy)-2,4,5,6-tetrahydrocyclopenta[c]thiophene (16.2 g, 60.6 mmol) in dimethylsulfoxide (140 ml). Add water (14 mL) and lithium chloride (7.0 g, 0.16 mol). Heat at reflux for 4 hours, cool and partition between water (150 mL) and methylene chloride (2×150 mL). Wash the organic phase with water (150 mL), dry (MgSO4) and pass through a silica gel plug to give 5-(carboethoxy)-2,4,5,6-tetrahydro-cyclopenta[c]thiophene. Dissolve 5-(carboethoxy)-2,4,5,6-tetrahydrocyclopenta[c]thiophene (6.68 g, 34.1 mmol) in ethanol (95%, 150 mL) and water (75 mL). Add potassium hydroxide (9.5 g, 0.17 mol) and stir at room temperature for 1 hour. Partition between water (150 mL) and ethyl ether (2×150 mL). Acidify the aqueous phase with hydrochloric acid to pH 1. Extract with methylene chloride (2×150 mL), dry (Na2SO4) and evaporate the solvent in vacuo to give 5-(carboxy)- 2,4,5,6-tetrahydrocyclopenta[c]thiophene.

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