R

sired aldehydes. For catalytic oxidation the oxoammonium salt was postulated as the active intermediate [10].

Thus isolation of oxoammonium salts on insoluble, cross-linked polymer supports was investigated together with integration of the active resins in polymerassisted solution phase synthesis [11]. These isolated oxoammonium salts could be employed in a water-free system with the intention of generating a highly reactive oxidizing agent that avoids over-oxidation to the acid, because of the absence of water.

The 4-hydroxy-TEMPO radical was coupled to 1% divinylbenzene polystyrene resin, using sodium hydride as base, yielding resin 1 with a loading of 0.93 mmol g-1 (Figure 3.6.3). ESR spectroscopy proved the presence of the free radical electron, because of the characteristic triplet signal as a result of coupling with the 14N nucleus. Oxidation of the radical 1 to the oxoammonium resin 2 was best performed with N-chlorosuccinimide. The oxidation is accompanied by a distinct color change from colorless to a bright orange-red for chloride as counter-ion and brown-red for bromide. Chloride proved to be a superior counter-ion, because it was more reactive and led to fewer by-products.

The versatility of the novel reagent was investigated with a diverse selection of alcohols at room temperature with 3 equiv. of the reagent for 1 h. Results from the oxidations can be summarized as follows. Clean and rapid quantitative conversion to the respective aldehyde or ketone product was observed for all benzylic, allylic, o^o

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