Oximes oxidations, manganese dioxide

Cycloaddition reactions of nitrile oxides continue to be the source of new isoxazoles and dihydroisoxazoles. The oxidation of a-hydroxyimino acids 1 by ammonium hexanitratocerium(IV) has provided a new method of generation of benzonitrile oxide and other nitrile oxides on the other hand the oxime 2 is simply dehydrogenated by this oxidant to produce benzoylnitrile oxide <99BSJ2277>. Manganese dioxide has also been used to oxidise aldoximes to nitrile oxides the reaction is most efficient with methyl (hydroxyimino)acetate <99TL5605>. ... 

Active manganese dioxide was used by Canonica in 19472 for the oxidation of oximes into nitrocompounds before the seminal publication of Ball et al. on the oxidation of vitamin A (76). Canonica prepared active manganese dioxide by reacting MnCb with KMn04. In fact the oxidation power of precipitated manganese dioxide is known since the 1870 s.3... 

The hydroxyimino (oxime) group can also be oxidized to a nitro group. For example, diethyl nitrosomalonate gives diethyl nitromalonate in 88% yield on treatment with manganese dioxide in glacial acetic acid for 24 hours at 30°.196... 

Manganese dioxide. 14,200-201 15, 197-198 18,230-231 19,210 20,237-238 Nitrile oxides An alternative method for generation of these reactive species from oximes is by oxidation with Mn02. 

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