Cyclic fatty esters: synthesis and characterization of methyl omega-(6-alkyl-3-cyclohexenyl) alkenoates
1982
Awl, R.A. | Frankel, E.N.
Diunsaturated C18 cyclic fatty acid methyl esters of known structure and configuration were synthesized as model derivatives of cyclic fatty acids formed in heat-abused vegetable oils for characterization and further biological evaluation. The Wittig reaction was used to prepare 5 pure methyl esters: 12-(3-cyclohexenyl)-11-dodecenoate, 11-(6-methyl-3-cyclohexenyl)-10-undecenoate, 10-(6-ethyl-3-cyclohexenyl)-9-decenoate, 9-(6-propyl-3-cyclohexenyl)-8-nonenoate and 8-(6-butyl-3-cyclohexenyl)-7-octenoate. Diels-Alder cycloaddition reactions between 1,3-butadiene and appropriate (E)-2-alkenals produced 3-cyclohexenal intermediates. The appropriate methyl .omega.-bromoesters and their triphenylphosphonium bromides were made and converted to their respective ylids with NaOCH3. The appropriate 3-cyclohexenals and phospho-ylids were reacted and the desired cyclic ester products were isolated in crude yields of 30-83% as liquids and fractionally distilled. The crude cyclic esters were purified either by preparative TLC or by saponification-esterification. Double bonds in purified cyclic esters were trans-isomerized and hydrogenated. Each derivative was characterized by IR, 1H-NMR, 13C-NMR, capillary GLC and GC-MS [gas chromatography-mass spectrometry]. On the basis of these analyses, no positional isomers were detected, Z-unsaturated isomers were produced in better than 90% purity and the alkyl and ester ring substituents were predominantly trans to each other.
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