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.