New Facile Synthesis of 3-Substituted 7,8-Dihydroquinolin-5(6H)-ones and [1]Benzopyrano[4,3-b]pyridin-5-ones Using 2-(Hetero)arylvinamidinium Salts

The method of cyclocondensation of 3-amino-2-cyclohexen-1-ones 2 or 4-aminocoumarin 3 with symmetrical 2-(hetero)arylvinamidinium salts 1 has been developed, providing an efficient synthetic pathway to access novel functionalized 3-substituted 7,8-dihydroquinolin-5(6R)-ones 4 or [1]benzopyrano[4,3-b]pyridin-5-ones 5 in good to excellent yields. All the aryl-substituted and heterocyclic-substituted vinamidinium salts undergo a facile electrocyclic ring closure to form pyridine ring with alpha,beta-unsaturated ketones. A possible mechanism for the formation of pyridine ring is proposed.