Selectivity controlled by ligand tuning in the palladium-catalysed cyclocarbonylation: Synthesis of new γ and δ lactones from a natural sesquiterpene

The cyclocarbonylation of homoallylic alcohols, derived from alpha-atlantone, catalysed by [Pd(Cl-2)L-2]/SnCl2] system, afforded new gamma and delta lactones as the main products with high selectivities. The regiochemical control depends on the nature of phosphines involved. Catalysts based on monophosphines with large cone angles such as tricyclohexyl phosphine produce the six-membered ring lactones with selectivities up to 80%, while diphosphines with wide bite angle such as xantphos are found to favor the five-membered ring lactones with up to 99% selectivity. Monocrystals of the gamma and delta lactones suitable for X-ray diffraction analysis have been obtained and the stereochemistry of the lactones 5a,a' and 6 have been elucidated. This study is the first example of an attractive catalytic transformation of one single natural sesquiterpene easily available from bio-renewable resources to obtain either -gamma- or delta-lactones. (C) 2015 Elsevier B.V. All rights reserved.