title: A gold-catalysed enantioselective Cope rearrangement of achiral 1,5-dienes.
abstract: Since the discovery of the Cope rearrangement in the 1940s, no asymmetric variant of the rearrangement of achiral 1,5-dienes has emerged, despite the successes that have been achieved with its heteroatom variants (Claisen, aza-Cope, and so on). This article reports 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-methylenecyclopropanes. The reaction proceeds at low temperature and the synthetically useful vinylcyclopropane 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 methylenecyclopropane moiety provides the thermodynamic driving force for the rearrangement and (3) metal complexation of the transition-state structure lowers the rearrangement barriers.
authors.affiliation: Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina                 27599-3290, USA.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Felix
authors.forename: Dieter
authors.initials: D
authors.lastname: Weber
authors.forename: Osvaldo
authors.initials: O
authors.lastname: Gutierrez
authors.forename: Dean J
authors.initials: DJ
authors.lastname: Tantillo
authors.forename: Michel R
authors.initials: MR
authors.lastname: Gagné
mesh_terms: D002384:Catalysis; D055598:Chemical Phenomena; D006046:Gold / Q000737:chemistry*; D011090:Polyenes / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D011090:Polyenes; D006046:Gold