Cu(II)-Catalyzed Oxidative Formation of 5,5'-Bistriazoles.

Copper(II) acetate under aerobic conditions catalyzes the formation of 5,5'-bis(1,2,3-triazole)s (5,5'-bistriazoles) from organic azides and terminal alkynes. This reaction is an oxidative extension of the widely used copper-catalyzed azide-alkyne "click" cycloaddition. The inclusion of potassium carbonate as an additive and methanol or ethanol as the solvent, and in many instances an atmosphere of dioxygen, promote the oxidative reaction to afford 5,5'-bistriazole at the expense of 5-protio-1,2,3-triazole (5-protiotriazole). If needed, tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) as a ligand additive further accelerates the formation of 5,5'-bistriazoles. A convenient procedure to prepare TBTA is also reported to facilitate the adoption of this method for preparation of 5,5'-bistriazoles. Aromatic azide-derived 5,5'-bistriazoles possess rigid axially chiral structures with a broad distribution of dihedral angles, which may be explored as chiral ligands in enantioselective catalysis if decorated with proper functional groups.