One-Pot Construction of β-Selective Quinolines with γ-Quaternary Carbon from Vinylquinolines with Active Ylides via Pd/Sc/Brønsted Acid Co-Catalysis

Vinyl-substituted N-heterocycles, as more challenging inert olefins with more stable reactivity, have brought about widespread attention in the reaction of aza-Michael addition or reduction coupling reaction. Here, we report a [Pd(η³-C₃H₅)Cl]₂/Sc(OTf)₃-catalyzed catalytic process accelerated by Brønsted acids with a β-selective aza-Michael addition to yield a γ-quaternary carbon from vinyl-substituted quinolines, diazos, and anilines/alcohols in one pot. The generation of anhydride analogues from Brønsted acid and the counter anion (OTf^-) of Lewis acid promotes the activation of the corresponding Lewis acid and the nearly quantitative transformation. Both π-cation and coordination interactions play pivotal roles in the activation of the vinyl-quinoline substrates by the activated Lewis acid Sc(OTf)₃. The control mechanistic evidence and DFT calculations presented a Pd/Sc/Brønsted acid co-catalyzed addition mechanism. The triple co-catalytic system provides a strategy for the activation of vinyl-quinolines with a linear selectivity containing γ-quaternary carbon, and the developed method shows a broad substrate scope varying from alkyl/aryl alcohols and amines which provides a general and rapid strategy for the quinoline-based diverse library construction.