Modular Access to Bridgehead Heterocycle‐Substituted Bicyclo[1.1.0]butanes via Late‐Stage Functionalization of Alkynylbicyclo[1.1.0]butanes

Strain‐release transformations of bicyclo[1.1.0]butanes are powerful methods for constructing four‐membered rings and bicyclo[n.1.1]alkane scaffolds of medicinal interest. However, the lack of efficient methods for the synthesis of bridgehead‐heterocycle‐substituted bicyclo[1.1.0]butanes limits their application in the synthesis of corresponding heterocycles. Herein, we disclose alkynylbicyclo[1.1.0]butanes (ABCBs) as versatile synthons: the strained bicyclobutane core remains unscathed while the alkyne handle undergoes mild, late‐stage cycloadditions to deliver triazole‐, isoxazole‐, free‐NH‐pyrrole, free‐NH‐pyrazole or silacyclohexene‐decorated BCBs that are otherwise difficult to access by conventional routes.