Hydroxylamine chlorite

Appropriate pyrido[2,3-d]pyrimidin-5-ones with formyl groups in the 6-position have been oxiized to piromidic (68) and pipemidic (69) acids, or to intermediates for these, using moist silver oxide, chromium trioxide (potassium dichromate), potassium permanganate or, alternatively, sodium chlorite/hydroxylamine-O-sulfonic acid. 6-Acetyl groups have been similarly oxidized using sodium hypobromite in aqueous dioxane, whilst 2-acetyl groups give dimethylaminomethylene derivatives en route to 2-pyrazolylpyrido[2,3-d]pyrimidines. 

Oxo salts of nitrogenous bases perchlorates, dichromates, nitrates, iodates, chlorites, chlorates, and permanganates of ammonia, amines, hydroxylamine, guanidine, etc. 

TEMPO and other organic nitroxyls have been used as catalysts in combination with numerous stoichiometric oxidants, such as sodium hypochlorite [24], PhI(OAc)2 [25], and sodium chlorite [26]. A number of recent studies have shown that NO -based redox cocatalysts enable these reactions to be conducted with O2 as the terminal oxidant [27]. The general catalytic cycle for these aerobic nitroxyl/NO -catalyzed alcohol oxidation reactions is depicted in Scheme 15.6a. A variation of this approach features halides as additives, in which the X2/HX redox couple is believed to mediate the NO2/NO and oxoammonium/hydroxylamine redox couples (Scheme 15.6b). 

The nitroxyl radical serves as a catalyst precursor which is oxidized by using different primary oxidants (e.g. sodium chlorite [327], electrochemical oxidation [328-330] or periodic acid [331]). The resulting oxoammonium cation is considered to be the true catalytic oxidant which is reduced to the corresponding hydroxyl-amine during the oxidation of the alcohol. Subsequently, the hydroxylamine is re-oxidized with a suitable stoichiometric oxidant to the nitroxyl radical. 

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