Expeditive Access to 2-Substituted 4H-Pyrido[1,3]oxazin-4-ones via an Intramolecular O-Arylation

Unreported 2-substituted 4H-pyrido[e][1,3]oxazin-4-ones are synthesized via an unprecedented intramolecular O-arylation of N-aroyl- and N-heteroaroyl-(iso)nicotinamides under microwave irradiations, in good to excellent yields. The broad applicability was demonstrated by 24 examples with a variety of substituents at the 2-position of the final compounds and 3 possible positions for the nitrogen atom of the pyridine ring. In addition, transformation of one of these compounds into 2-hydroxypyridyl-substituted 1,2,4-triazole and 1,2,4-oxazinone was realized. This approach opens a rapid access to a new bicyclic heteroaromatic chemical series with high potential in medicinal chemistry.