Chemistry of Heterocyclic Compounds, Vol. 33, No. 7, 1997 SYNTHESIS OF MESOIONIC 3-ARYL- AND 3-HETARYL-1,2,3,4OXATRIAZOL-5-ONES S. A. Shevelev, I. L. Dalinger, V. I. Gulevskaya, and T. I. Cherkasova The mesoionic 3-R- 1,2,3,4-oxatriazol-5-ones (3-R- 1,2,3,4-oxatriazolium 5-olates, 3-R-azasydnones) present significant interest due to their antihypertensive activity . However, the existing range of 3-arylazasydnones (1) is fairly limited. Thus, 3-hetarylazasydnones have been unknown until the present time. We found a method for the synthesis of (I) consisting in the reaction of bromonitroformaldehyde N-arylhydrazones (II) with alkali metal nitrates or ammonium nitrate in DMF or acetonitrile at - 2 0 ~ for several hours. It was communicated in the work  that the reaction of the hydrazones (II) (Ar = C6H5 and substituted C6H5) with NaNO 3 in DMF results in the formation of products of the substitution of the bromine atom by the nitrate grouping. However, not in one case did we f'md such compounds. The method allows the synthesis not only of the compounds (I) with various aryl (C6H5, p-CH3C6H4, m-CH3OC6H4, p-BrC6H4, p-F, and p- and m-NO2C6H4) substituents, described in the literature [1, 3], but also hetarylsydnones. The last were shown, using the examples of 3-(4-nitropyrazol-3yl)azasydnone (Ia) and 3-(1,2,4-triazol-3-yl)azasydnone (Ib).