RUTHENIUM-CATALYZED ALLYLATION OF PRIMARY ALCOHOLS BY ALLYLIC ACETATES - A NOVEL SYNTHESIS OF ALPHA,BETA-UNSATURATED KETONES

Certain ruthenium complexes show high catalytic activity in the synthesis of alpha,beta-unsaturated ketones from primary alcohols and allylic acetates. Here, pi-allylruthenium intermediates apparently operate as nucleophiles rather than as electrophiles. Among the carbon-carbon bond forming reactions promoted by transition-metal complexes, allylic alkylations, especially those catalyzed by palladium complexes, have been extensively studied and have been successfully applied in organic synthesis.1 In contrast, comparatively little is known about alkylation reactions involving pi-allylruthenium intermediates, despite the current interest in the synthesis of pi-allylruthenium complexes.2 In the course of studies of catalysis by ruthenium complexes,3 we found that pi-allylruthenium intermediates act as nucleophiles rather than as electrophiles in reactions with aldehydes to give homoallylic alcohols.4 This reactivity is quite different from that of pi-allylpalladium complexes which generally act as electrophiles.5 Because many biologically important natural products possess an enone functionality, and because the synthesis of such compounds has been the target of much effort over the last decade,6 we attempted to apply ruthenium catalysis to the synthesis of enones. Therefore, in this paper, we describe a novel synthesis of alpha,beta-unsaturated ketones from primary alcohols and allylic acetates via pi-allylruthenium intermediates (eq 1).