Abstract Dehydrobromination of N-arylhydrazones of bromonitroformaldehyde (at 20° C) in the presence of alkali and ammonium salts of strong mineral acids, HNO 3, silica gel, and Al 2 O 3 forms mesoionic 3-aryl-1, 2, 3, 4-oxatriazol-5-ones (3-arylazasydnones). The effect of the electronic properties of the aryl substituent on the course of the reaction is evaluated. This evaluation is used to develop a general method for preparing 3-arylazasydnones ...