The synthesis of 4-bromo-,4,5-dichloro(1), 4-fluoro-, and 4-methyl- -2H-1,3(3H)-oxazine-2,6-dione, as well as an improved synthesis of 2H-1,3(3H)- oxazine-2,6-dione, by reaction of trimethylsily azide with the corresponding maleic anhydride is described. This route is superior to other methods for prepn. of 4-substituted oxazinediones. N-Methylation of the oxazinedione ring may be readily accomplished with Me2SO4 buffered by NaHCO3. Chem. Abstr. Vol. 82, 140036j.