Divergent synthesis of (quinoxalin-2-yl)-1,3-oxazines and pyrimido[1,6-a]quinoxalines via the cycloaddition reaction of acyl(quinoxalinyl)ketenes

A facile synthetic approach towards two distinct quinoxaline-based heterocyclic scaffolds has been developed from the cycloaddition of acyl(quinoxalinyl)ketenes with carbodiimides. The described reaction represents the first example of a divergent synthesis based on acyl(quinoxalinyl)ketenes providing (quinoxalin-2-yl)-1,3-oxazines or pyrimido1,6-a]quinoxalines depending on the type of the acyl substituent in the ketenes. The key reactants, acyl(quinoxalinyl)ketenes, are generated in situ via the thermal decarbonylation of readily available pyrroloquinoxaline oxo-derivatives. The proposed diversity-oriented synthesis provides facile access to a library of skeletally diverse pharmaceutically interesting quinoxaline-based heterocycles from inexpensive reagents.