Synthesis of Indazole Derivatives Involving Aryl Nitrene Species

Significance

A mild, efficient, one-pot, and high-yielding synthesis of indazole derivatives from hetero­cyclic o-nitrobenzaldimines is reported. The key step involves the intramolecular reductive cyclization of an aryl nitrene leading to N-N bond formation. The starting materials are readily available from phenethyl amines or tryptamines by the classical Bishler-Napieralski reaction (E. C. Cortes, E. C. Romere, G. F. Ramirez J. Heterocycl. Chem. 1994, 31, 1425-1427) and the reductive reaction is carried out under mild and short-time conditions.