An efficient solvent- and catalyst-free synthesis of bicyclic pyridones with high molecular diversity via cascade reaction

Two efficient cascade routes for synthesis of substituted bicyclic pyridines under solvent-and catalyst-free conditions have been developed. One is conducted by refluxing the reaction mixture of heterocyclic ketene aminals (HKAs), triethoxymethane and dicarbonyl compounds. The other one is proceeded with HKAs and diethyl ethoxymethylenemalonate (EMME) under ultrasound irradiation. Both routes for preparation of bicyclic 2-pyridones carried out with low cost and easy available substrates and achieved diversity of target compounds in good yields efficiently and environmental-friendly.