Unexpected Rearrangement of Unsaturated Lactones to Give Tricyclic Furopyrrolidinones

An unexpected cyanide-mediated rearrangement of conjugated lactones is described, providing access to novel tricyclic furopyrrolidinones. This reaction occurs in a stoichiometry- and substrate-dependent manner, induced by multiple additions of cyanide to α,β,γ,δ-unsaturated lactones bearing suitable aryl substituents, providing products with adjacent ether, nitrile, and lactam functionalities. Single-crystal X-ray diffraction (SCXRD) studies of two products support the stereochemical assignments, providing evidence of a dynamic equilibrium process.