The nitrosation of secondary nitro derivatives into ketones or oximes depending on the nitro substituents has been reinvestigated. The reaction efficiently takes place under neutral conditions, thus allowing acid-sensitive substrates to be converted in very good yields. The generation of nitrosating species under such mild conditions is unprecedented. Mechanistic investigations strongly suggest that they result from the nucleophilic attack of the nitrite anion on the aci-nitro(nate) form of the secondary nitroalkane. The latter acts in turn as an autocatalyst for its own transformation by means of the nitrosating species generated in situ from it.
Nitrolic acids are prepared in good yields from primary nitroalkanes or primary alkyl bromides. Upon heating in THF, they afford the corresponding nitrile oxides under neutral conditions. In the presence of dipolarophiles, isoxazoles are obtained in yields up to 95%. For the less stable alkoxycarbonyl-and arylnitrolic acids the crude nitrolic acids can be directly engaged in the cycloaddition reaction.
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