Transition Metal-Free γ-C(sp3)–H Functionalization of Enaminones for Methylene 1,2-Dihydropyridine Synthesis and Application in Fused Tricyclic Pyrido[1,2-a]indole Construction

The annulation reaction of β-methyl enaminones with alkynones leading to the synthesis of methylene-functionalized 1,2-dihydropyridines (1,2-DHPs) has been realized. In the presence of only Cs2CO3, 1,2-DHPs have been synthesized with a broad scope and generally high efficiency via the novel transformation of the γ-C(sp3)–H bond in enaminones. In addition, the application of the method has been demonstrated by the one-step transformation of the 1,2-DHP products into fused tricyclic scaffolds featuring an indole–pyridine hybrid via dual C–H activation.