Intermolecular Formal [2π + 2σ] Cycloaddition of Enol Silyl Ethers with Bicyclo[1.1.0]butanes Promoted by Lewis Acids.

Silyl enol ethers react with bicyclo[1.1.0]butanes (BCBs) through Yb(OTf)3-promoted formal [2π + 2σ] cycloaddition reactions to furnish bicyclo[2.1.1]hexanes (BCHs). This new reaction tolerated a wide range of enol silyl ethers and BCBs. Furthermore, the amplification experiments and synthetic transformations of the cycloaddition compounds further highlighted their practicality.