Copper-Catalyzed Formal [2 + 2 + 2] Cycloaddition of Triynes for the Construction of Heterohelicenes.

The construction of heterohelicenes is an important topic in organic synthesis due to their broad applications in chemistry and materials. Transition-metal-catalyzed [2 + 2 + 2] cycloaddition of alkynes is an efficient protocol for the synthesis of heterohelicenes. However, most of the established methods require noble-metal catalysis and an oxidative cyclometalation pathway. Herein, we report a copper-catalyzed formal [2 + 2 + 2] cycloaddition of triynes via vinyl cations, enabling the rapid construction of heterohelicenes in high yields. Moreover, preliminary results were obtained for the corresponding catalytic enantioselective reaction.