Biomimetic Carbene‐Catalyzed Oxidations of Aldehydes Using TEMPO

Transition-metal-free organocatalytic oxidations of various aldehydes proceed with the TEMPO radical as a mild organic oxidant; the resulting TEMPO esters are formed in moderate to excellent yields (see scheme). N-Heterocyclic carbenes (NHCs) are efficient catalysts and activate aldehydes for electron-transfer reactions. The TEMPO esters are readily hydrolyzed and the nitroxide can be regenerated by aerobic oxidation.