4,5-Dichloro-2H-1,3-oxazine-2,6(3H)-dione

4-Bromo-2H-1,3-oxazine-2,6(3H)-dione

The title compound, C₄H₂BrNO₃, is one of a series of three substituted oxauracils prepared as precursors in the preparation of 1-aza-1,3-butadienes. Although each structure has identical potential for N—H⋯O inter­molecular hydrogen bonds, each forms a distinctive inter­molecular network. In the title compound, there are two independent mol­ecules in the asymmetric unit, with a non-crystallographic twofold screw-like relationship between them. The two indpendent mol­ecules are linked by an inter­molecular N—H⋯O hydrogen bond. In the crystal structure, this hydrogen-bonded pair is linked to translationally related mol­ecules through further inter­molecular N—H⋯O hydrogen bonds, forming one-dimensional chains along [100]. The crystal structure also has short Br⋯O=C inter­molecular contacts with distances of 2.843 (4) and 2.852 (4) Å.

4-Methyl-2H-1,3-oxazine-2,6(3H)-dione

In the title compound, C₅H₅NO₃, the planar (maximum deviation = 0.075 Å for the ring O atom) mol­ecules form N—H⋯O hydrogen bonds in a zigzag chain (C—O⋯N bond angle ≃ 140°) between glide-related mol­ecules.