Synthesis of 1,2,3-triazoles by CuSO4 reduction using PhB(OH)2 as reducing agent.

From the first studies on the synthesis-synthesis catalysis of functionalized 1,2,3-triazoles it has been evident that the catalyst is based on a copper species in the 1+ oxidation state. Of the three oxidation states of this metal (0, 1+ and 2+), the cuprous ion (1+) is the least stable because it is easily oxidized1 in the presence of air to Cu2+ or dismutated to Cu0 and Cu2+. However, the oxidation of Cu0 to Cu1+ and the reduction of Cu2+ to Cu1+ can be carried out by simple procedures. Thus, different methods have been written to generate the catalytic specificity; the most usual ones are based on: (1) in situ reduction of Cu(II) salts by using sodium ascorbate or other reducing agents, (2) oxidation of metallic copper with a mild oxidant or Cu1+ dismutation and (3) direct addition of a Cu(I) complex.2