A novel bis-lactonisation of naphtho- and phenanthro-1,2-dioxines with malonate nucleophiles

Abstract

Malonate nucleophiles add in a conjugate fashion to substituted naphtho- and phenanthro-1,2-dioxines to furnish functionalised bis-lactones in high yield and with high de. The basicity of the malonate nucleophile is sufficiently mild to rearrange the 1,2-dioxines to yield the transient cis-γ-hydroxy enone species with no further Kornblum-DeLaMare rearrangement. The cis-γ-hydroxy enones readily undergo conjugate addition by malonate nucleophiles in a highly diastereoselective fashion. An intramolecular domino cyclisation then ensues yielding the observed bis-lactones. The relative configuration of the bis-lactone series was established by 1- and 2-D [1]H, [1][3]C NMR techniques and further confirmed by single crystal X-ray analysis.