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]‐2 H ‐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‐2 H ‐chromen‐3‐yl)methyl)2‐oxo‐2 H ‐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]‐2 H ‐chromen‐2‐ones. This study suggests new structural assignments for previous reports and proposes a re‐examination of the described multicomponent reaction.