CCC pincer Ru complex-catalyzed C–H vinylation/6π-E-cyclization of aldimines for constructing 4H-pyrido[1,2-a]pyrimidines

Abstract

An unusual cascade C–H activation, vinylation and 6π-electrocyclization of 2-pyridyl aldimines with vinyl bromides/triflates was achieved using catalysis with a unique CCC pincer NHC–Ru(III) complex (Cat B). This reaction was found to enable a rapid and diverse synthesis of polycyclic 4H-pyrido[1,2-a]pyrimidine derivatives in mostly good to high yields, and with a broad substrate scope. A mechanistic study suggested the formation of a semi-opened Ru(III) intermediate chelating/activating the aldimine, and the occurrence of single-electron transfer (SET) to generate a vinyl radical, followed by vinylation and then an intramolecular 6π-electrocyclization of 1N,3N-hexatrene to form the product. This protocol provides a convenient approach for preparing and seeking new drug candidates.