Sequential four-component protocol for the synthesis of pyrido[1,2-a]pyrimidin-6-one derivatives in water

A highly efficient and environmentally benign synthesis of N-fused heterocyclic compounds including pyrido[1,2-a]pyrimidine-6-one moiety is successfully achieved via a sequential four-component reaction. The process involves the formation of diversely substituted 9-nitro-1,2,3,4,7,8-hexahydro-6H-pyrido[1,2-a]pyrimidin-6-ones from the reaction of Meldrum’s acid, benzaldehydes, 1,1-bis(methylthio)-2-nitroethylene and various diamines in the presence of p-toluene sulfonic acid (PTSA) as an acidic catalyst in water as a green solvent. The salient features of the present methodology are easily available starting materials, the use of water as environmentally benign solvent, simple execution, applicable to a wide range of starting materials and good to excellent yields.