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6,8-Dinitro-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]oxazin-1-one, C9H5N5O6, (I), a potential diuretic, and its acetyl­acetone derivative (E)-2-(2-hy­droxy-4-oxopent-2-en-3-yl)-6,8-dinitro-2,4-dihydro-1H-benzo[b][1,2,4]triazolo[4,3-d][1,4]oxazin-1-one, C14H11N5O8, (II), both crystallize from methanol but in centrosymmetric and noncentrosymmetric space groups, respectively. To the best of our knowledge, this is the first report of crystal structures of benzoxazine–triazole fused systems. The acetyl­acetone group in (II) exists as the keto–enol tautomer and is oriented perpendicular to the triazol-3-one ring. Of the two nitro groups present, one is rotated significantly less than the other in both structures. The oxazine ring adopts a screw-boat conformation in (II), whereas it is almost planar in (I). N—H...N and N—H...O hydrogen bonds form centrosymmetric dimers in (I), while C—H...O inter­actions associate the mol­ecules into helical columns in (II).
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