A complete study on the preparation of original halogen-containing 4H-pyrido[e][1,3]oxazin-4-ones and their transformation into 1,2,4-oxadiazoles and 1,2,4-triazoles is presented. Starting from pyridyl-imide sodium salts, the efficiency of the intramolecular O-arylation was studied on three series of compounds, with different fluoro-, chloro-, and bromophenyl substituents at the C-2 position. The final halogenated compounds are of interest as new synthons for future functionalisation. We also present the discovery of a new, rapid, and complementary access to 2-substituted 4H-benzo[e][1,3]oxazinones. Finally, the one-step transformation of some of these pyrido-oxazinones into the corresponding hydroxypyridyl-substituted 1,2,4-oxadiazoles and 1,2,4-triazoles was explored, and the regioselectivity of the reaction was proved by X-ray crystallography.