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

• Palladium-catalyzed cyclocarbonylation of a natural sesquiterpene affords new gamma- and delta-lactones.
• High conversions and good selectivities in lactones are obtained.
• Regioselectivity can be controlled by the nature of the ligand and a control by the substrate itself is also observed.
• It is an attractive catalytic transformation of a sesquiterpene easily available form bio-renewable ressources.

The cyclocarbonylation of homoallylic alcohols, derived from α-atlantone, catalysed by [Pd(Cl2)L2]/SnCl2] system, afforded new γ and δ 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 γ and δ 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 γ- or δ-lactones.

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