Concise synthesis of spirocyclic, bridged gamma-butyrolactones via stereospecific, dyotropic rearrangements of beta-lactones involving 1,2-acyl and delta-lactone migrations

Dyotropic processes involving unprecedented 1,2-acyl migrations provide access to novel spirocyclic, bridged keto-gamma-lactones from a series of fused, tricyclic-beta-lactones, available via biscyclization of ketoacids including a new asymmetric variant. In addition, a spirocyclic bis-gamma-lactone was generated via a dyotropic process involving a 1,2-beta-lactone/sigma-lactone interchange. Overall, this sequence provides a simple, two-step process for conversion of diketoacids to complex spiro5.n]alkanes bearing a contiguous tertiary carbon center, a quaternary carbon center, and a tertiary alcohol in the form of a bridging gamma-lactone.