Isoxazoles reaction with oxidizing agents

The gold-catalysed cyclization/oxidative 3+2-cycloadditions of 1,5-enynes (57) with nitrosobenzene produced substituted isoxazoles (59) with high stereocontrol. The nitrosobenzene also acts as an oxidizing agent in this reaction. Alkenylgold carbocations (58) are important intermediates in this reaction sequence (Scheme 16). ... 

A somewhat related sequence leads to trilostane (111), a compound that inhibits the adrenal gland more specifically the agent blocks some of the metabolic responses elicited by the adrenal hormone ACTH in experimental animals. Reaction of the hydroxy-methylene derivative 108, obtained from testosterone, with hydroxylamine gives the corresponding isoxazole (109). Oxidation of the C-4,5 double bond by means... 

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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