Copper-Catalyzed\nIntermolecular [2 + 2 + 2] Annulation\nof Diynes with Alkynes: Construction of Carbazoles

Transition-metal-catalyzed [2 + 2 + 2] annulation of\nalkynes is\nan efficient pathway for the synthesis of aromatic compounds. However,\nmost of the established methods require noble metal catalysts. Herein,\nwe report a copper-catalyzed intermolecular [2 + 2 + 2] annulation\nof diynes with alkynes through vinyl cation intermediates, enabling\nthe atom-economical preparation of biologically important carbazole\nskeletons. The reaction shows good regioselectivity in the reaction\nof aryl(alkyl)alkynes. Moreover, preliminary results have also been\nobtained for the related catalytic atroposelective transformation.\nThis reaction represents a rare example of non-noble-metal-catalyzed\nintermolecular [2 + 2 + 2] annulation of ynamides through the vinyl\ncation pathway.