A novel convenient acid-catalyzed acylation of enaminodiones with acylbenzotriazoles via soft enolization has been developed for the direct synthesis of hard-to-reach 5-acyl-3-oxy-4-pyrones. The important advantages of the reaction include broad substrate scope, mild conditions, scalability, and readily isolation of products by crystallization without the use of chromatography. Further modification of the pyrone ring and synthesis of various azaheterocycles via ring-opening transformation have been demonstrated for the preparation of potential scaffolds for inhibition of metalloenzymes.

This work describes the synthesis of 3-hydroxy-3,4-dihydropyrido[2,1-c][1,4]oxazine-1,8-diones, their tautomerism, and reactivity towards binucleophiles. These molecules are novel and convenient building-blocks for the direct construction of biologically important polycyclic pyridones via an oxazinone ring-opening transformation promoted with ammonium acetate or acetic acid. In the case of o-phenylenediamine, partial aromatization of the obtained heterocycles proceeded to form polycyclic benzimidazole-fused pyridones (33–91%).