Pyridine-Boryl Radical-Catalyzed [2 + 2] Cycloaddition of Bicyclo[1.1.0]butanes with Alkenes

Bicyclo[2.1.1]hexanes (BCHs) represent an intriguing class of structurally rigid hydrocarbons that can serve as the bioisosteres of benzenoids in medicinal chemistry. Methods for the synthesis of BCHs are, however, limiting. Reported herein is a facile synthesis of BCHs via a strain-release-driven [2 + 2] cycloaddition of bicyclo[1.1.0]butanes (BCBs) with alkenes facilitated by a pyridine-boryl radical catalyst. The mild reaction conditions, broad substrate scope, and decent functional group tolerance of this protocol render it appealing in relevant fields of drug design and synthesis. Theoretical mechanistic studies reveal a radical relay mechanism involved. Synthetic applications of the products are conducted.