Bisallylation of Zirconacyclopentenes and Ring-Closing Metathesis: A Route to Eight-Membered-Ring Compounds

The cyclization of various enynes with the Negishi reagent provides the corresponding bicyclic zirconacyclopentenes, which after exposure to allyl chloride in the presence of a catalytic amount of copper(I) chloride, undergo bisallylation to furnish 1,9-decadienes in good yields (42–89%). The dienes are subjected to ring-closing metathesis to afford bicyclic compounds with [6.3.0]bicycloundecane (8,5-fused ring system) or [6.4.0]bicyclododecane (8,6-fused ring system) frameworks in good to excellent yields (52–92%). Selective monoallylation of a selected zirconacyclopentene followed by carboxyethylation with ethyl chloroformate gives rise to the corresponding ester, which after metalation and reaction with allyl bromide, furnishes a 1,9-decadiene. Ring-closing metathesis then yields the expected eight-membered cyclic product in 92% yield. This procedure constitutes a new pathway to bicyclic carbocyclic systems starting from 1,ω-enynes.