Precise Modulation of BCB Reactive Sites via Lewis/Brønsted Acid Switching for the Synthesis of Spirocycles and Bridged Frameworks.

Bicyclo[1.1.0]butanes (BCBs), which possess multiple switchable reactive sites, serve as the most direct modular scaffolds for constructing benzene ring bioisosteres. Herein, we describe the precise modulation of BCB reactive sites through Lewis/Brønsted acid switching to enable the synthesis of challenging spirocycles and bridged frameworks. The divergent reaction outcomes, arising from the precise control of catalysts over the switchable reactive sites of BCBs, are achieved without any substrate modification.