Aerobic Copper-Catalyzed Organic Reactions

Oxygen is a highly atom-economical, environmentally benign, and abundant oxidant, which makes it ideal in many ways. The high activation energies in the reactions of oxygen require that catalysts be employed. A number of alternate approaches have been developed allowing oxidation chemistry to be used safely across a broader array of conditions. For example, use of carbon dioxide instead of nitrogen as a diluent leads to reduced flammability. Alternately, water can be added to moderate the flammability allowing even pure oxygen to be employed. New reactor designs also allow pure oxygen to be used instead of diluted oxygen by maintaining gas bubbles in the solvent, which greatly improves reaction rates and prevents the build up of higher concentrations of oxygen in the head space. Oxidation occurs through two primary mechanisms. In acidic or activated substrates, deprotonation can occur, followed by single-electron oxidation to form the key radical species that then reacts with molecular oxygen.