UNUSUAL STEREOCHEMICAL RESULTS IN THE REACTION OF ALPHA-LITHIO DERIVATIVES OF BICYCLIC SULFOXIDES

The stereochemistry of the reaction of the lithio derivatives of two sets of isomeric 3-thia[3.2.1]octane-3-oxides with electrophiles such as benzyl bromide, acetone and D2O has been studied. Introduction of deuterium always occurred cis to the S=O bond as expected on the basis of earlier results described by Marquet for the related thiane-S-oxides. In contrast, benzyl groups were introduced either cis or trans to the existing S=O bond. The results are most readily rationalized in terms of a planar configuration at the a-carbanion center. The unexpected cis benzylations are due to steric hindrance of the preferred approach anti to the S=O bond by either the ethano bridge or the 8-endo methyl group.