The Structures Obtained from the Oxidation of 3-Amino-1H-indazole in Basic Conditions According to Hünig and Pozharskii.

The oxidation of 3-amino-1H-indazole was reported independently by Hünig and Pozharskii approximately 50 years ago and proposed to yield an azo compound via a Baeyer-Mills-type mechanism. However, the structural assignment lacked complete evidence, leaving the identity of the obtained product uncertain. To unambiguously determine the correct structure, the oxidation under basic conditions was reinvestigated, revealing two distinct products depending on the loading of t-BuLi. The obtained compounds were systematically characterized by 1D/2D NMR techniques and X-ray diffraction, leading to the conclusion that the Hünig's "deep-red" compound corresponds to the structure assigned as (E)-1-[(3H-indazo-3-ylidene)amino]-1H-3-amine, whereas Pozharskii's "orange" compound is indeed an azoazole, featuring an E-configuration in the azo bond rather than the Z-configuration reported in 1977. This investigation resolves discrepancies among previous literature reports regarding the oxidation of 3-amino-1H-indazole and unifies them within a single coherent framework.