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

Abstract

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.