Lithium Hydroxide → (1aS,5aR)-1,1,2-trimethyl-1,1a,5,5a-tetrahydro-3-thia-cyclopropa[a]pentalene-4-carboxylic acid

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Reaction Conditions

Reaction Steps

Alternatively, (1aS,5aR)-1,1,2-trimethyl-1,1a,5,5a-tetrahydro-3-thia-cyclopropa[a]pentalene-4-carboxylic acid is also obtained by the following procedure: To a solution of sodium (2.80 g, 122 mmol) in ethanol (400 mL) a solution of mercaptoacetic acid ethyl ester (14.64 g, 122 mmol) in ethanol (40 mL) is added. The solution is stirred for 5 min before (1S,5R)-2-(1-chloro-(E)-ethylidene)-6,6-dimethyl-bicyclo[3.1.0]hexan-3-one (15.0 g, 81.2 mmol) in ethanol (40 mL) is added dropwise. The solution becomes slightly warm (approx. 30° C.) and turns orange to brown. A fine precipitate forms. Stirring is continued at rt for 1 h. Then, a solution of sodium (2.24 g, 97.5 mmol) in ethanol (75 mL) is added rapidly and the mixture is heated to 75° C. for 1 h. A 2N aq. solution of LiOH (75 mL) is added and stirring is continued at 75° C. for 2h, then at rt for 16 h. About ⅔ of the solvent is removed in vacuo, the remaining mixture is diluted with water (250 mL) and extracted with DCM (200 mL). The organic extract is washed twice with 1 N aq. (100 mL). The combined aqueous layers are acidified by adding 2N aq. HCl and extracted three times with diethyl ether (3×300 mL). The organic extracts are dried over MgSO4 and evaporated. The remaining residue is suspended in acetonitrile, filtered, washed with additional acetonitrile and dried under high vacuum to give the title compound (12.02 g) as a pale yellow to beige crystalline powder.

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