A three-component reaction of 4-Hydroxycoumarin, 2-Aminopyridine, and Aryl Aldehydes: Synthesis of enolate salts of 2-Aminopyridinium Biscoumarins

Abstract

Multicomponent reaction (MCR) of aryl aldehydes, 4-hydroxycoumarin, and 2-aminopyridine gave the corresponding 2-aminopyridinium enolate salts of biscoumarins in the presence of zirconyl oxynitrate as a catalyst. This differs from other reports that claim the formation of chromeno[4,3-d]pyrido[1,2-a]pyrimidin-6-ones and 3-[aryl(pyridin-2-ylamino)methyl]-2H-chromen-2-ones. Spectroscopic methods confirmed the chemical structures of all the novel compounds. Moreover, single-crystal X-ray diffraction confirms the molecular structure of the product 2-aminopyridin-1-ium-3((4-fluorophenyl)(4-hydroxy-2-oxo-2H-chromen-3-yl)methyl)2-oxo-2H-chromen-4-olate. These salts' NMR and IR data closely resemble the previously reported data on chromeno[4,3-d]pyrido[1,2-a]pyrimidin-6-ones and 3-[aryl(pyridin-2-ylamino)methyl]-2H-chromen-2-ones. This study suggests new structural assignments for previous reports and proposes a re-examination of the described multicomponent reaction.