Stereoselective Preparation of Bicyclo[3.3.0]octanones From the Products of Aprotic Conjugate Addition of Lithiated Allylic Sulfoxides to Cyclopent-2-enone and Enolate Trapping With Methyl Cyanoformate

The lithium enolates arising by aprotic conjugate addition of lithiated but-2-enyl sulfoxides and a phosphine oxide to cyclopent-2-enone react efficiently with methyl cyanoformate to give the corresponding methyl 5-oxocyclopentanecarboxylates in good yields. The sulfoxides are smoothly deoxygenated with tributylphosphine diiodide in ether at 0�, and the resulting sulfides undergo intramolecular cyclization in the presence of tin(IV)chloride to give methyl oxobicyclo [3.3.0] octanecarboxylates , again in good to excellent yields. The cyclizations are highly stereoselective in that the syn- and anti-stereochemistries of the enolate trapped products obtained from (E)-and (Z)- sulfoxides are quantitatively reflected in the products obtained from the cyclization reactions.