Tandem dienyne ring-closing metathesis of alkynyl silaketals for the formation of bicyclic siloxanes

The tandem dienyne ring-closing metathesis of alkynyl silaketals containing two tethered olefins was achieved with second generation Grubbs NHC-ruthenium carbene complex to provide bicyclic siloxanes in good to excellent yield. Silaketals synthesized from homoallylic or bishomoallylic alcohols via base-catalyzed alcoholysis of trialkynylsilanes were well tolerated in the metathesis process and generated ring systems of various sizes. Removal of the silicon tether was achieved through protodesilylation with fluoride to afford stereochemically defined (1E,3Z)-dienes.