Recent Progress in (3+3) Cycloadditions of Bicyclobutanes to Access Bicyclo[3.1.1]heptane Derivatives

Bicyclo[3.1.1]heptane (BCHeps) derivatives, which serve as three-dimensional (3D) bioisosteres of benzenes and the core skeleton of several terpene natural products, are garnering growing interest for their synthesis. The (3+3) cycloadditions of bicyclobutanes (BCBs) represent an attractive method for efficiently accessing (hetero)BCHep skeletons with 100% atom economy. Herein, we give a brief summary of recent achievements in this approach for the synthesis of diverse BCHep derivatives, emphasizing our recent progress in the initial palladium-catalyzed (3+3) cycloadditions of bicyclobutanes with vinyl oxiranes.