Preparation of deuterated methyl 6,9,12-octadecatrienoates and methyl 6,9,12,15-octadecatetraenoates

Methyl 6,9,12-octadecatrienoate-15,15,16,16-d4 was obtained by Wittig coupling between 6,6,7,7-tetradeutero-3-nonenyltriphenylphosphonium iodide, 8, and the aldehyde ester, methyl 9-oxo-6-nonenoate. Methyl 6-oxohexanoate, obtained by ozonolysis of cyclohexene, was coupled in a Wittig reaction with [2-(1,3-dioxan-2-yl)ethyl]triphenylphosphonium bromide to give methyl 8-dioxanyl-6-octenoate. This compound was transacetalized to methyl 9,9-dimethoxy-6-nonenoate, which was then hydrolyzed to the aldehyde ester. For the preparation of compound 8, the tetrahydropyranyl ether of 2-pentynol was deuterated with deuterium gas and tris-(triphenylphosphine)chlororhodium. The tetradeuterated tetrahydropyranyl ether was converted to the bromide with triphenylphosphine dibromide, and the bromide was coupled with 3-butynol by means of lithium amide in liquid ammonia to give 3-nonynol-6,6,7,7-d4. Hydrogenation over Lindlar's catalyst converted the deuterated alkynol to 3-nonenol-6,6,7,7-d4. This deuterated alkenol was converted to the bromide with triphenylphosphine dibromide, then to the iodide with sodium iodide in acetone, and finally to 8 with triphenylphosphine in acetonitrile. Methyl 6,9,12,15-octadecatetraenoate-12,13,15,16-d4 was obtained by Wittig coupling between methyl 9-oxo-6-nonenoate and 3,4,6,7-tetradeutero-3,6-nonadienyltriphenylphosphonium iodide, 15. For the preparation of compound 15, the bromide obtained from the reaction of 2-pentynol with triphenylphosphine dibromide was coupled with 3-butynol with lithium amide in liquid ammonia. The resulting 3,6-nonadiynol was deuterated with deuterium gas in the presence of P-2 nickel, and the resultant deuterated nonadienol was converted to 15 through the bromide and iodide. The final products were separated from isomers formed during the synthetic sequences by silver resin chromatography.