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

Abstract

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 TEMPOmediated 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.

Expedient Immobilization of TEMPO by Copper‐Catalyzed Azide‐Alkyne [3+2]‐Cycloaddition onto Polystyrene Resin

“…Alternatively, polymer bound co-oxidants have been proposed to overcome limitations associated with the necessity to employ stoichiometric amounts of the co-oxidant in solution, requiring additional purification steps. [9] We report here the simple and efficient preparation of a new polystyrene-supported TEMPO by using click chemistry as a practical tagging method and demonstrate its high activity for the oxidation of alcohols using bleach or molecular oxygen as a co-oxidant.…”

Oxoammonium‐ and Nitroxide‐Catalyzed Oxidations of Alcohols

“…Polymers containing the chlorite ion, such as 27, have been used in these reactions. 44,191 In fact, a polymeric nitroxide (60, discussed below), polymeric secondary oxidant 27, and a polymeric dihydrogen phosphate buffer (28) have been used to carry out oxidations in a multiphase system (see also "Experimental Procedures" section). Scope.…”

4‐CH3CONH–TEMPO/Peracetic Acid System for a Shortened Electron‐Transfer‐Cycle‐Controlled Oxidation of Secondary Alcohols

“…Subsequently,i ntermediate b was formed after nucleophilic attack of alcohol a to the oxoammonium species, giving the product andT EMPOH by the hydrogen transfer. [24] As aw hole, the catalytic system shortened the electron-transfer cyclec ompared with the previous systems, [17] avoidingt he cycle with halidesa se lectron-transfer mediators.…”