Copper-catalyzed ultrasonic-promoted coupling of acetylene analogs, dialkyl azo dicarboxylate, and benzazoles to assemble tricyclic fused-ring [1,2,3]triazolo[3,4-b][1,3]benzazole analogs

An unprecedented copper-catalyzed reaction of acetylene analogs with dialkyl azo di-carboxylate and benzazole analogs via a cross-coupling sequence was reported. A library of tria-zolobenzazole fused ring systems including [1,2,3] triazolo [3,4-b] [1,3] benzothiazole, [1,2,3] triazolo [3,4-b] [1,3] benzoxazole and [1,2,3] triazolo[3,4-b][1,3]benzimidazole structures were obtained in moderate to excellent yields under very mild reaction conditions. Structural confirma-tion of the final products became possible using different methods like spectroscopy and ele-mental analysis. The control experiments indicated C-H activation of acetylene by copper salts, followed by cycloaddition between a 2-(phenylethynyl)benzo[d]azol-3(2H)-yl anion and azo di-carboxylate as the key mechanistic feature. The broad substrate scope with simple and easily af-fordable starting materials, as well as mild reaction conditions are the noticeable attributes of this methodology, which provides facile access to the desired products.