Tandem radical cyclization of acyclic homoallylic xanthates: cyclopentannulated .gamma.-thionolactone and .gamma.-lactones

The first tandem radical cyclization of linear homoallylic xanthates was explored. Homoallylic santhates prepared from α,β-unsaturated esters were easily cyclized by tin hydride with an radical initiator to give the corresponding thionolactone annulated cyclopentane skeleton in a high yield. The stereochemistry of cyclized products was also discussed. Thionolactones obtained were oxidized chemoselectivity with m-CPBA under neutral condition to afford γ-lactones in a high yield