Practical TEMPO‐Mediated Oxidation of Alcohols using Different Polymer‐Bound Co‐Oxidants

Hypochlorite and chlorite exchange resins are evaluated as co‐oxidants or oxidants, respectively, for the oxidation of alcohols to the corresponding aldehydes, ketones or carboxylic acids. Polymer‐bound hypochlorite can act as a co‐oxidant in TEMPO‐mediated oxidations of alcohols. The formation of aldehydes only works under weakly acidic conditions. However, the cheap hypochlorite exchange resin is less efficient as co‐oxidant compared to the use of ionically immobilised bisacetoxybromate(I) anions. In contrast, the chlorite exchange resin is a highly potent co‐oxidant for the preparation of carboxylic acids from the corresponding primary alcohols in the presence of TEMPO. It is demonstrated that in this case also the resin acts as a polymer‐bound co‐oxidant for both oxidation steps. Yields are commonly excellent as is also demonstrated for examples taken from natural product synthesis which include acid labile glycosides. In most cases, work‐up of this heavy metal‐free oxidation is kept to a minimum. It often includes filtration followed by removal of the solvent.