Studies on the sigmatropic nitro migration of N-nitropyrazoles

초록

The direct nitration of pyrazole, using nitric acid or mixture of nitric acid and sulfuric acid, leads to substitution in the 4 position. 1-Nitropyrazole undergoes intramolecular rearrangement at 120~190℃ to form 3(5)-nitropyrazole in high yield. The 1,2-sigmatropic shift of the nitro group is considered as the first step of this rearrangement, which is followed by fast rearomatization of intermediates. Thermal N to C migration of NO2 is not restricted to pyrazole. Analogous migration were found in N-nitroindazole, triazole, and imidazole. We will discuss thermal rearrangement of N-nitropyrazoles.