Abstract
Molecular oxygen is a highly atom-economical, environmentally benign, and abundant oxidant. However, the large activation energies in the reactions of oxygen and formation of undesirable intermediates such as superoxide, hydroperoxide, and hydroxyl radical have prevented utilization of molecular oxygen as oxidant. Among recently reported systems that employ dioxygen as the terminal oxidant, noteworthy is alcohol oxidation method reported by Stahl and co-workers. The system consisting of copper complex, TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl), and base is suited for widespread use in synthetic chemistry and practically applicable level. Muldoon and co-workers developed one-pot synthesis of cyanide or N-heterocycles from alcohols based on Stalh’s reports. In parallel with reports from synthetic chemistry field, Hayton group and other groups reported isolation of TEMPO transition-metal complexes which can react with organic substrates. Those works suggested that the reactivity of TEMPO toward alcohols enhanced by the complexation with metal ion, where the nitrogen atom of TEMPO works as an acceptor of proton rather than oxygen atom in C-H bond cleavage of substrates.
