Copper-Catalyzed Formal [5 + 1] Annulation of Diynes with 1H-Indole-2-ethanols: Construction of Tetrahydropyrano Indoles.

Transition-metal-catalyzed annulation of diynes with nucleophiles is a powerful tool for constructing valuable complex (hetero)cycles. However, reports on the cascade annulation of diynes with dinucleophiles are rare and confined to noble-metal catalysts, narrow diyne scopes, and specific reaction types. Herein, we describe a copper-catalyzed formal [5 + 1] annulation of 1,6-diynes with 1H-indole-2-ethanols via vinyl cations, leading to the concise and practical synthesis of tetrahydropyrano indoles. Significantly, this protocol represents the first non-noble-metal-catalyzed annulation of diynes with dinucleophiles.