A New Strategy for the α-Vinylation of Ketones : Application to an Enantioselective Synthesis of Sesquiterpene (+)-α-Elemene

School of Chemistry, University of Hyderabad, Hyderabad-500 046

Manuscript received 29 July 1998

A new, simple and preparatively useful protocol for the construction of a-vinyl ketones, particularly those bearing a quaternary carbon centre, from the corresponding alkenes has been devised. Our four-step strategy consists of dichloroketene addition, base catalysed ring contraction to 'push-pull' cyclopropane esters, reduction and eliminative cyclopropane fragmentation to unravel the α-vinyl ketone moiety. The generality of this approach has been demonstrated with a few representative olefins and good regio- and stereocontrol has been observed. As an application of this methodology, an enantioselective synthesis of sesquiterpene hydrocarbon (+)-α-elemene (42) from R-(+)-limonene (43) has been accomplished.