Total Synthesis of Racemic and Optically Active Coronafacic Acids

Abstract (±)-Methyl 3-ethyl-4-oxotricyclo[4.3.0.01,5]nonane-5-carboxylate (4), prepared by the stereoselective alkylation of methyl 4-oxotricyclo[4.3.0.01,5]nonane-5-carboxylate, was reduced with zinc borohydride, and the resultant hydroxy ester was treated with p-toluenesulfonyl chloride to give a mixture of α,β-unsaturated esters, having hydrindan skeletons. The mixture was submitted to hydroboration-oxidation to afford a keto ester, which was hydrolyzed to (±)-coronafacic acid (2). A diastereomeric mixture of l-menthyl 3-ethyl-4-oxotricyclo[4.3.0.01,5]nonane-5-carboxylates, prepared by a modification of the synthesis of (±)-4, was resolved by column chromatography on silica gel, and each diastereomer was converted into (+)-2 and (−)-2 in a similar way as (±)-2.