Palladium-Catalyzed Sequential Intramolecular Annulation/[2σ + 2π] Cycloaddition of 5-Allenyloxazolidine-2,4-Diones and Bicyclobutanes.

Bicyclo[2.1.1]hexanes (BCHs) are important three-dimensional bioisosteres of substituted benzenes. Although mono- and fused-BCH scaffolds have been extensively studied, spiro-BCH derivatives remain relatively underexplored. Herein, we report a palladium-catalyzed tandem intramolecular annulation/strain-release [2σ + 2π] cycloaddition between 5-allenyloxazolidine-2,4-diones and bicyclo[1.1.0]butanes (BCBs). This method provides efficient and concise access to a novel class of γ-lactam-spiro-BCH scaffolds in moderate to excellent yields. The transformation exhibits broad substrate scope, good scalability, and versatile downstream derivatization of the products.