Metal-Free C(sp3)–Si Activation Enables Regiocontrolled [4+2] Cycloaddition to Benzosilacycloethers

Abstract

We herein report a sustainable, transition-metal-free strategy for the inverse site-selective [4+2] cycloaddition of benzosilacyclobutanes with activated ketones, enabled by the dual role of DMSO as a mild Lewis base and green solvent. This operationally simple method achieves selective C(sp³)–Si bond cleavage under mild conditions, bypassing traditional transition-metal catalysts and their associated environmental burdens. Notably, the reaction exhibits reversed regioselectivity (Csp³–Si vs. Csp²–Si activation) compared to conventional metal-catalyzed systems, granting access to distinct benzosilacycloether scaffolds. Mechanistic studies via DFT calculations reveal the origin of selectivity and the pivotal role of DMSO in directing the transformation. The protocol showcases broad functional group tolerance and aligns with green chemistry principles by avoiding toxic metals, harsh conditions, and wasteful additives, offering a step toward sustainable heterocycle synthesis.