An efficient synthesis of 2H-indazoles via reductive cyclization of 2-nitrobenzylamines induced by low-valent titanium reagent

An efficient and improved synthesis of 2H-indazoles via reductive cyclization of 2-nitrobenzylamines induced by low-valent titanium reagent (TiCl4/Zn) is described. In this reaction triethylamine (TEA) was used to control the pH value. This method has the advantages of easily accessible starting materials, convenient manipulation, higher yield, shorter reaction time, and wider substrate scope.