Isoxazolines reaction with oxidizing agents

Another methodology for the in situ preparation of nitrile oxide is the dehydro-halogenation of hydroxymoyl chlorides vrith triethylamine. Hydroxymoyl chlorides are accessible by the reaction of aldoximes vrith chlorinating agents such as NCS (N-chlorosuccinimide). Isoxazolines of C50 and C70 [293-295] with R = Ph, alkyl, 4-C5H4OCH3 4-C5H4CHO, amino acid [305], dialkoxyphosphoryl [296, 297] or ferrocene [298] have been synthesized in ca. 20 0% yields. The latter reaction is slower than the dehydration of nitroalkanes and requires one equivalent of hydroxymoyl chloride whereas excess nitroalkane is necessary for an optimum reaction [293]. 

A reaction that is set to gain momentum within the field of macromolecular science over the next few years is the cycloaddition of nitrile oxides with alkynes and norbornenes to form isoxazoles and isoxazolines respectively (Scheme 2.6). Whilst strictly a catalyst-free reaction, the in situ generation of the requisite nitrile oxide from the respective oxime precursor typically makes use of a mixture of a dipole generating agent (such as Chloramine-T) and a weak base (such as aqueous NaHC03). 

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