Annulation of Allylsilanes and Bicyclo[1.1.0]butanes with Lewis Acids

Bridged bicyclic scaffolds are of increasing importance as benzene bioisosteres in medicinal chemistry. Herein, we describe Lewis acid-catalyzed [2π + 2σ] and [4π + 2σ] formal cycloadditions between allylsilanes and 2-vinyl allylsilanes with bicyclo[1.1.0]butanes (BCBs), affording functionalized bicyclo[2.1.1]hexanes (BCHs) and bicyclo[4.1.1]octanes (BCOs). Notably, by tuning the Lewis acid and solvent system, we realized chemoselective control of the [2π + 2σ] and [4π + 2σ] cycloaddition reaction pathways for 2-vinyl allylsilanes, thereby attaining chemodivergent syntheses of BCHs and BCOs. This reaction features a broad substrate scope, operational simplicity, and mild conditions. The straightforward transformation of silyl groups to hydrogen and other functionalities under mild conditions demonstrated the silyl group as a "traceless" activating group of alkenes, enabling the formal cycloaddition of simple alkenes and BCBs. Consequently, this reaction significantly expands synthetic access to bridged bicycles and represents an advancement for the application of allylsilanes in cycloaddition reactions.