Asymmetric Büchner reaction and arene cyclopropanation via copper-catalyzed controllable cyclization of diynes

Abstract

The asymmetric Büchner reaction and related arene cyclopropanations represent one type of the powerful methods for enantioselective dearomatization. However, examples of asymmetric Büchner reactions via a non-diazo approach are quite scarce, and the related arene cyclopropanation based on alkynes has not been reported. Herein, we disclose an asymmetric Büchner reaction and the related arene cyclopropanation by copper-catalyzed controllable cyclization of N-propargyl ynamides via vinyl cation intermediates, leading to chiral tricycle-fused cycloheptatrienes and benzonorcaradienes in high yields and enantioselectivities. Importantly, this protocol represents an asymmetric arene cyclopropanation reaction of alkynes and an asymmetric Büchner reaction based on vinyl cations. Asymmetric Büchner reactions are an effective methodology to bring about synthetic complexity from the common benzene motif, but effective, general catalytic methods are scarce. Here, the authors present divergent asymmetric arene dearomatization from ynamides using copper catalysis, wherein the catalytic cycle proceeds via a putative vinyl cation intermediate.