Oxidation of aldoximes

Oxidation of aldoximes 327 with sodium hypochlorite or NBS is one of the best-known methods for generation of nitrile oxides (Equation 73) <1999BCJ2277>. 

Electrochemical oxidation of aldoximes using halide ions as mediators afforded the corresponding nitrile oxides in the anode compartment, which were simultaneously reduced to nitriles by cathodic reduction (equation 15). Sodium chloride affords the best result among the supporting electrolytes (Cl > Br > 1 > C104 > TsO ). Accordingly, the electrochemical reaction of oximes carried out in the presence of dipolephiles yielded isooxazolines (equation 16). 

The oxidation of aldoximes and amidoximes (methods Q and R) is not a practical process but rather a way of formation. The reactions have been described because oxadiazoles have been isolated among a lot of other oxidation products. 

Fukunishi K, Kitada K, Naito I (1991) A facile preparation of iminoxy dimers by hydrogen peroxide/peroxidase oxidation of aldoximes. Synthesis 237-238... 

Apart from a few stable species, nitrile oxides exhibit a high tendency toward dimerization to furoxans for this reason, several methods have been developed for the in situ generation of such dipoles in the presence of the desired acceptor. The most common procedures involve thermal or base-mediated deydrohalogenation of hydroxymoyl halides, oxidation of aldoximes, and dehydration of primary nitroalkanes <1984CHEC(6)1>. 

Under radical conditions, aldehydes are readily oxidized hy NBS to acid bromides. The oxidation of aldoximes to nitrile oxides using NBS and Triethylamine in DMF is superior to the use of aqueous hypochlorite. Tosylhydrazones are cleaved by reaction with NBS in methanol, and hydrazines and hydrazides are oxidized to azo cort5)ounds. ... 

FORMATION OF ISOXAZOLINES AND ISOXAZOLES VIA DIPOLAR CYCLOADDITION BY CATALYTIC OXIDATION OF ALDOXIMES WITH HYDROGEN PEROXIDE AND W(VI) PEROXO COMPLEXES... 

Hereinafter we wish to report the results relative to the oxidation of aldoximes by hydrogen peroxide catalyzed by W(VI) peroxopolyoxo complexes. In the presence of alkynes or alkenes it is possible to obtain isoxazolines and isoxazoles respectively in very good yields. Implication of such findings will be discussed at the light of nitrile oxides cycloaddition chemistry and on the basis of W(VI) peroxo complex reactive behavior. 

IBX has also been used for the preparation of the 3,5-disubstituted isoxazolines 865. The oxidation of aldoximes 863 with IBX produces the respective nitrile oxides, which then undergo 1,3-dipolar addition with an alkene component 864 to give final products 865 (Scheme 3.345) [1182]. 

Isoxazoles display a range of biological activities, such as anti-inflammatory, antimicrobial, anticancer, and antinociceptive, that justify a constant effort in the development of new synthetic strategies. New syntheses of isoxazoles 1 and isQxazolines 2 via 1,3-dipolar cycloaddition (1,3-DC) of alkynes and alkenes with nitrile oxides were described (130L4010). The 1,3-dipoles were generated by oxidation of aldoximes catalyzed with hypervalent iodine species formed in situ from catalytic iodoarene and oxone as a terminal oxidant, in the presence of hexafluoroisopropanol (HFIP) in aqueous methanol solution. 

A one-pot synthesis ofbenzo[rf]isoxazole-4,7-diols 4 was efficiently performed in aqueous medium via 1,3-DC of nitrile oxide and benzoquinone intermediates generated by oxidation of aldoxime and phenol derivatives with iodobenzene diacetate. Such a strategy was also applied to synthesize various polynuclear isoxazole systems (13JOC8386). Benzo[isoxazole derivatives were regioselectively obtained by 1,3-DC of nitrile oxides (and nitrones) with 3-boryl- and 3-silylbenzynes (13JOC2965). 

Zhdankin and coauthors [92] showed that nitrile oxides 119 can be generated by hypervalent iodine-catalyzed oxidation of aldoximes 118 using oxone as a terminal oxidant (Scheme 29). These in situ generated nitrile oxides 119 reacted with several alkenes and alkynes to afford the corresponding isoxazolines 121 and isoxazoles 120 in moderate to good yields. 

Complex M(AAOPD), (18) (M = Co or Cu), catalyses the oxidation of aldoximes, ketoximes and carboxylic acids by dioxy iodobenzene (oxidant) in the presence of imidazole to corresponding carbonyl products in high yields. The rate of oxidation of oximes in the presence of Cu(AAOPD) is higher than that with Co(AAOPD) no such effect is observed in the oxidation of carboxylic acids. " ... 

Furazan-A-oxides (furoxanes) 104 (Scheme 30) are isolated as a result of the nitrile oxide dimerization when chloro-oximes 101 are treated with bases in the absence of dipolarophiles [21,49, 50]. Oxidation of aldoxime 99 with nitric acid gives furoxan 104 [Rp=H(CF2)8] in 50 % yield [51]. Similarly, furoxane 104 (RF=CgF5)... 

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