Gold(I)-Catalysed Cyclisation of Alkynoic Acids: Towards an Efficient and Eco-Friendly Synthesis of γ-, δ- and ϵ-Lactones

The improved synthesis of γ-, δ- and ϵ-lactones using a dinuclear N-heterocyclic carbene (NHC)-gold(I) catalyst is reported. This solvent-free process provides access to γ- and δ-lactones in high regio- and stereoselectivity. Reactions were performed at low catalyst loadings and without the need for any additives. The use of a digold pre-catalyst provides a new synthetic route to functionalised ϵ-lactones, poorly accessible using previous methodologies. (Figure presented.).