Reductive Cyclization of o-Nitrophenylazophenols to Benzotriazoles

Significance

Demonstrated is an efficient cyclization of o-nitrophenylazophenols to aryl tria­zoles in water using powdered zinc as the reductant. A simple work-up procedure is presented in which no extraction using organic solvents was required, and the products were obtained by filtration from the acidified reaction mixture. This avoidance of organic solvents makes the reported procedure potentially useful from industrial and environmental points of view. The substrate scope was fairly well studied. Lowering the reaction temperature as well as lowering the concentration of alkaline leads to decreased yields. No metals other than zinc as reductants were studied.