PIDA-Mediated Intramolecular N-N Bond Formation to Access 2-Aminoindazoles and 2,2 '-Biindazoles

A synthesis of 2-aminoindazole and 2,2'-biindazole derivatives from corresponding hydrazones using phenyliodine(III) diacetate (PIDA) as oxidant is reported at ambient temperature. This oxidative intramolecular cyclization reaction proceeds through the formation of the N-N bond. This protocol is metal-free, operationally simple, has a short reaction time, and proceeds in ethyl acetate (preferred green solvent). Indazole core moieties are well established for their biological activity similarly 2-aminoindazoles may also possess biological significance. A plausible reaction pathway has been reported based on a few control experiments.