Solvent-Free Synthesis of 4H-Pyrido[1,2-a]pyrimidin-4-ones Catalyzed by BiCl3: A Green Route to a Privileged Backbone

An extensive array of 4H-pyrido[1,2-a]pyrimidin-4-ones have been synthesized from commercially available 2-aminopyridines and -oxo esters with excellent yields under solvent-free conditions. The reaction, catalyzed by cheap and nontoxic BiCl3, proceeds with short reaction times under mild conditions and normal atmosphere. Only water and alcohol are formed as co-products in this green reaction.