CO2-Activation for ?-Butyrolactones and Its Application in the Total Synthesis of (±)-Heteroplexisolide E

An efficient nickel(0)-catalyzed highly regio- and stereoselective hydrocarboxylation of homopropargylic alcohols with ZnEt2 in the presence of CO2 (1 atm, balloon) to synthesize a-alkylidene-?-butyrolactones is described. The catalyst is highly active and can be applied for the synthesis of (optically active) mono- or bicyclic a-alkylidene-?-butyrolactones with excellent regio- and stereoselectivity and good functional group tolerance. The potential of the reaction has been demonstrated in the first synthesis of (+/-)-heteroplexisolide E.