Since its discovery in the 1940's, no asymmetric variant of the Cope rearrangement of achiral 1,5-dienes has emerged, this despite the successes that have been achieved with a number of its heteroatom variants (Claisen, aza-Cope, etc). We report herein the first example of an enantioselective Cope reaction that starts from an achiral diene.  The new gold(I) catalyst derived from double Cl�-abstraction of ((S)-3,5-xylyl-PHANEPHOS(AuCl)2), has been developed for the sigmatropic rearrangement of alkenyl-methylene cyclopropanes.  The reaction proceeds at low temperature and the synthetically useful vinyl cyclopropane products are obtained in high yield and enantioselectivity.  Density functional theory calculations predict that: 1) the reaction proceeds via a cyclic carbenium ion intermediate, 2) the relief of strain in the methylene cyclopropane moiety provides the thermodynamic driving force for the rearrangement, and 3) metal complexation of the transition state structure lowers the rearrangement barriers.

Gold-catalyzed enantioselective Cope rearrangement of achiral 1,5-dienes

243rd National Meeting (2012)

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