A gold-catalysed enantioselective Cope rearrangement of achiral 1,5-dienes

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, etc.). 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

Catalytic enantioselective synthesis of quaternary carbon stereocentres

Quaternary carbon stereocentres-carbon atoms to which four distinct carbon substituents are attached-are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials

Synthesis of heterocyclic compounds via gold-catalysed enyne rearrangements

Syntheses of heterocycles using different gold-catalysed rearrangements of enynes are discussed in this chapter. The term skeletal rearrangement has been used in a broad sense to include reactions involving cyclopropyl gold carbene intermediates formed by initial enyne cyclisation, which can undergo many different transformations to give a wide range of heterocyclic structures. Other transformations involving rearrangement of propargylic esters and [3,3]-rearrangement (concerted or stepwise comprising metallic intermediates), as well as special cases, have also been covered. References to earlier work in this area and to recent reviews have been included, but the focus of the chapter is to present recent developments, interesting cases and an overview on how subtle differences in the enyne starting materials, the catalyst used or the reaction conditions can alter the reaction pathway increasing the structural diversity towards complex heterocyclic structures of high value