Leveraging triatropic rearrangements for stereoselective skeletal reshuffling

Pericyclic reactions transform simple precursors into architecturally complex products with exquisite stereocontrol, making them central tools in synthesis. Here, we report a class of pericyclic reactions, called triatropic rearrangements, wherein three σ-bonds are broken concomitantly with the formation of two σ-bonds and one π-bond, all in a single transition state. Within this mechanistic manifold, carbon-oxygen bonds in epoxides are stereoselectively converted into carbon-carbon bonds in a process mediated by organoboron reagents. Epoxycycloalkanes undergo highly chemo-, regio-, and stereoselective carbon migration to furnish ring-contracted products with broad generality. This strategy also enables enantioselective 1,2-hydride migrations for linear epoxide substrates. The combination of this ring contraction protocol with [4+2] cycloadditions provides a distinct "[4+2-1]" strategy for the stereoselective construction of complex cyclopentanes in a modular fashion.