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%).

A two-stage synthesis of 5-aroyl-2-aryl-3-hydroxypyridin-4(1H)-ones (56–66% overall yields) was carried out by refluxing 5-aroyl-3-(benzyloxy)-2-(het)aryl-4H-pyran-4-ones with ammonium acetate in AcOH and subsequent debenzylation. The prepared N-unsubstituted 4-pyridones exist in the pyridone tautomeric form.