Isoxazolones pyrolysis

In contrast to the isoxazolones, the isomeric 4//-oxazolin-5-ones which lack the weak N—O bond usually lose only CO upon pyrolysis. Thus, FVP of a variety of compounds 354 at 600°C gives the acylketenimines 355167. The 2//-oxazolin-5-ones do lose CO2 to give iminocarbenes, which may undergo rearrangement, as in the formation of 357 from... 

Disubstituted 5-isoxazolones 169 (R R = alkyl or aryl) are converted into acetylenes 170 by the combined action of sodium nitrite and iron(II) sulphate in aqueous scetic acid a plausible mechanism is shown in equation 24 . Aminoacetylene (172) has been produced by flash-vacuum pyrolysis of the isoxazolones 171 (R=Me or Ph) it was observed by low-temperature IR spectroscopy and by its collision activation mass spectrum (CAMS). Aminoacetylene is also formed by pyrolysis of the derivative 173 of Meldrum s acid the product, an equilibrium mixture of the ketenes 174 and 175, decomposes above 680°C to aminoacetylene ". ... 

Flash pyrolysis of 4-arylmethylidene-3-methyl-5(4//)-isoxazolones (127) yields phenylacetylenes with alkoxy, chloro, dimethylamino and hydroxy substituents. The reaction proceeds via an arylmethylidene carbene as has been described for a... 

Further examples in the weU-estabHshed use of isoxazolones as precursors for substituted pyrrole synthesis include pyrolysis of the esters 45 to give the pyrroles 46 (Scheme 9 2001ARK(vii)88). 

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