Copper-Catalyzed Alkylalkynylation of [1.1.1]Propellane under Photocatalyst- and Ligand-Free Conditions.

Strain-release difunctionalization of [1.1.1]propellane has emerged as a powerful strategy for the construction of benzene bioisosteres. Herein, we report a copper-catalyzed alkylative alkynylation of [1.1.1]propellanes with terminal alkynes and cyclobutanone oxime esters. This transformation proceeds under mild photocatalyst- and ligand-free conditions, providing a cost-effective and practical alternative to existing photoredox-based systems. The reaction features broad substrate scope and good functional group tolerance and is applicable to the late-stage modification of complex molecules. Importantly, this protocol can be extended to [3.1.1]propellane, providing efficient access to alkynylated bicyclo[3.1.1]heptanes as valuable meta-benzene bioisosteres. Given the versatility of both alkynyl and cyano functionalities, this method offers a practical platform for the rapid construction and diversification of bicycloalkane scaffolds.