Regioselective Synthesis of 2<i>H</i>‑Indazoles Using a Mild, One-Pot Condensation–Cadogan Reductive Cyclization

An operationally simple and efficient one-pot synthesis of 2<i>H</i>-indazoles from commercially available reagents is reported. <i>Ortho</i>-imino-nitrobenzene substrates, generated via condensation, undergo reductive cyclization promoted by tri-<i>n</i>-butylphosophine to afford substituted 2<i>H</i>-indazoles under mild reaction conditions. A variety of electronically diverse <i>ortho</i>-nitrobenz­aldehydes and anilines were examined. To further extend the scope of the transformation, aliphatic amines were also employed to form <i>N</i>2-alkyl indazoles selectively under the optimized reaction conditions