Synthesis of Quinoline Derivatives via Cu-Catalyzed Cascade Annulation of Heterocumulenes, Alkynes, and Diaryliodonium Salts.

CuOTf-catalyzed substituent-controlled cascade [2 + 2 + 2] and [4 + 2] annulation reactions among heterocumulenes, alkynes, and diaryliodonium salts were achieved. Various quinoline derivatives could be obtained in good yields with excellent selectivity. This methodology provided a novel pathway to activate heterocumulenes via a unique highly reactive cationic intermediate. The reaction process was well elucidated by density functional theory calculations.