ANRORC reactions of 3-methyl-1,4-dinitro-1H-pyrazole with arylhydrazines

Reactions of 3-methyl-1,4-dinitro-1H-pyrazole with phenylhydrazine and some C-substituted derivatives were studied. The reactions with arylhydrazines containing electron-withdrawing substituents afforded 1-Aryl-5-methyl-4-nitro-1H-pyrazoles only. Unexpectedly, mixtures of two regioisomers, 1-Aryl-3-methyl-4-nitro-1H-pyrazoles and 1-Aryl-5-methyl-4-nitro-1H-pyrazoles, were obtained from the reaction with phenylhydrazine or 4-methyl-and 4-fluoro-derivatives. An ANRORC (Addition of the Nucleophile, Ring Opening, Ring Closure) mechanism was proposed for the reaction.