Copper/TEMPO-Catalyzed Aerobic Alcohol Oxidation: Mechanistic Assessment of Different Catalyst Systems

Combinations
of homogeneous Cu salts and 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) have emerged as practical and efficient catalysts
for the aerobic oxidation of alcohols. Several closely related catalyst
systems have been reported, which differ in the identity of the solvent,
the presence of 2,2′-bipyridine as a ligand, the identity of
basic additives, and the oxidation state of the Cu source. These changes
have a significant influence on the reaction rates, yields, and substrate
scope. In this report, we probe the mechanistic basis for differences
among four different Cu/TEMPO catalyst systems and elucidate the features
that contribute to efficient oxidation of aliphatic alcohols.