The cycloaddition reactions of nitrile oxides with jojoba oil have been investigated. The nitrile oxides were generated <i>in situ</i> by two principal routes: (i) by the base catalysed dehydration of nitromethyl compounds using tolylene-2,4-diisocyanate (the Mukaiyama method), and (ii) by thermolysis of nitro-acetate and -malonate esters (the Shimizu method). In order to faciliate the identification of modified jojoba products and establish optimum conditions for reaction with the unsaturation present in jojoba oil, the cycloaddition reactions of nitrile oxides with selected model alkenes were studied. Terminal alkenes afforded 5-substituted-2-isoxazolines regiospecifically in 21-68% yield, whereas mid-chain alkenes proved to be less reactive and gave a regioisomeric mixture of 4,5- disubstituted isoxazolines (19-69&37 yield). Cycloadditions to unsaturated lipids were also examined; methyl oleate and oleyl acetate both yielded stereospecifically a regioisomeric mixture of <i>cis-</i> isoxazolines when reacted with ethoxycarbonylnitrile oxide. The geometric isomer of methy oleate, methyl elaidate, afforded a mixture of <i>trans</i>-4,5-disubstituted isoxazolines. The ratio of regioisomers in all cases was shown to be 1:1 by the use of high field <SUP>13</SUP>C NMR, which detected small differences in chemical shifts of ring carbons. Proton NMR was also used to characterise lipid isoxazolines, assignment of their spectra being facilitated by comparison with those of model compounds. FAB mass spectrometry enabled the detection of parent ions for these isoxazolines. Application of the Shimizu method to ethyl nitroacetate provided a novel approach to formonitrile oxide; with model alkenes 3-unsubstituted isoxazolines were formed in 19-36% yields. In contrast, ethyl nitroacetate reacted with isocyanate and base to form <i>N</i>-phenyl-α-ethoxycarbonyl-α-nitroacetamide which was itself thermolysed to produce an amide nitrile oxide. Further exploitation of this approach using di-isocyanates lead to the generation of di-nitrile oxides. Cycloaddition reactions of the analogous azomethine oxide, <i>C,N</i>-diphenylnitrone, led to formation of the corresponding ring-saturated isoxazolidine moieties.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:653825 |
| Date | January 1990 |
| Creators | Leslie, Morag Garden |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12407 |
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