Submitted to: Association for the Advancement of Industrial Crops Conference
Publication Type: Abstract Only
Publication Acceptance Date: October 17, 2000
Publication Date: N/A
Technical Abstract: The 1,3-dipolar cycloaddition reaction between a nitrile oxide and an alkene has been known for many years and provides convenient access to the five-membered heterocyclic ring system known as delta 2- isoxazolines. Typically, this reaction is carried out by converting an aldoxime into its corresponding hydroxamic acid halide with a halogenating agent. Subsequent base catalyzed dehydrohalogenation of the hydroxamic acid halide generates the desired nitrile oxide which is trapped by an olefin. The aldoxime method was examined as a practical method into fatty acid ester isoxazolines from unsaturated fatty acid ester derivatives. Aldoximes were converted into their corresponding nitrile oxides in situ using household bleach and catalytic triethylamine. The 1,3-dipolar cycloaddition reactions between the nitrile oxides and olefinic substrates, such as methyl 10-undecenoate, gave fatty ester delta 2-isoxazoline heterocycles. Good yields and excellent regioselectivity were obtained when methyl 10-undecenoate was used as the olefin. The isoxazolines obtained from these reactions have been reductively cleaved to obtain delta 2-hydroxy ketones in excellent yields. Currently, vegetable oil derived disubstituted olefins, such as methyl oleate and methyl linoleate, are being examined for their ability to undergo these 1,3-dipolar cycloadditions. The straightforward synthesis of delta 2-isoxazolines, their potentially interesting properties coupled with their synthetic versatility make them an interesting class of compounds, and further research should make this methodology an attractive way to functionalize vegetable oils.