Preparation of Long-Chain bet-Enaminones and beta-Diketones from Long-Chain 3,5-Disubstituted Isoxazole Compounds

摘要

A series of long-chain compounds containing the beta-enaminone functionality were prepared in yields ranging from 71 to 88% from their corresponding long-chain 3,5-disubstituted isoxazole precursors utilizing a Raney nickel-catalyzed reductive ring-opening procedure.These newly prepared multifunctional compounds were subsequently hydrolyzed under mild acidic conditions(pH 4-5)to give their corresponding long-chain beta-diketones in yields ranging from 79 to 98%.Both the beta-enaminone and beta-diketone functionalized compounds were characterized by NMR,IR spectroscopy,GC-MS,and m.p.The mass spectra for these two classes of compounds,derived by utilizing electron impact ionization,gave distinctive McLafferty rearrangement fragmentation ions that clearly established the newly introduced functionality to reside at the C-2 and C-4 positions of the lipid's alkyl chain.~1H NMR spectra of the pure beta-diketone compounds were complex owing to the keto enol tautomerism displayed by the beta-diketone moiety.In solution the beta-diketone compounds were shown to exist mainly in the enolic tautomeric form.Long-chain beta-diketone compounds are known to the relatively common constituents of some plant waxes,and the overall rocedure starting from soybean methyl esters provides a complementary approach to prepare these types of compounds.