Copper-catalyzed cascade cyclization reaction of 2-haloaryltriazenes and sodium azide: selective synthesis of 2H-benzotriazoles in water.

A new approach to the synthesis of 2H-benzotriazoles is described. This strategy is based on the copper-catalyzed C-N coupling of 2-haloaryltriazenes or 2-haloazo compounds with sodium azide and the intramolecular addition of nitrene to N=N bonds. This approach allows the synthesis of various N-amino- and N-aryl-2H-benzotriazoles in water, in good to excellent yields. The procedure is simple and the starting materials and catalyst are easily available, offering a practical and convenient synthetic route to 2-substituted benzotriazoles.