γ-Lactones as templates in ring-closing metathesis: Enantioselective synthesis of medium sized carbocycles fused to butyrolactones

A methodology for accessing enantiomerically enriched carbocyclic systems fused to γ-lactones is described. Key steps are the stereoselective synthesis of highly substituted γ-lactones and ring-closing metathesis of the suitable ramifications. The process permits the choice of stereochemistry, regioselectivity and ring size of the fused compounds.