SYNTHESIS OF MESOIONIC 3-ARYL(HETARYL)-1,2,3,4-OXATRIAZOL-5-ONES BASED ON N-ARYL- AND N-HETARYLHYDRAZONES OF BROMONITROFORMALDEHYDE

Dehydrobromination of N-arylhydrazones of bromonitroformaldehyde (at 20°C) in the presence of alkali and ammonium salts of strong mineral acids, HNO3, silica gel, and Al2O3 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 with various substituents including novel 3-hetarylazasydnone derivatives of pyrazole, 1,2,4-triazole and pyridine. Aromatic electronic effects (s I , s R , s m , s p ) of the mesionic 1,2,3,4-oxatriazol-5-on-3-yl moiety are determined by 19F NMR. A scheme is proposed for the dehydrobromination of the bromonitroformaldehyde N-arylhydrazones that includes the intermediate N-aryl-C-(nitro)nitrilimines, ArN – – N=C + NO 2 , with subsequent isomerization of the latter into 3-arylazasydnones. Authors: S. A. Shevelev, I. L. Dalinger, V. I. Gulevskaya, T. I. Cherkasova, V. M. Vinogradov, B. I. Ugrak, and A. M. Starosotnikov. English Translation in Chemistry of Heterocyclic Compounds , 1999, 35 (3), pp 363-373 http://link.springer.com/article/10.1007/BF02259369