Syntheses of deuterated methyl 9,15‐octadecadienoate and methyl 9,12,15‐octadecatrienoate geometric isomers

Methyl 9,15-octadecadienoate-6,7-d2 isomers (12) were obtained by Wittig coupling between methyl 9-oxononanoate-6,7-d2 (6) and 6-nonenyltriphenylphosphonium bromide (11). Compound 11 was prepared from methyl 6-nonenoate (8) by reduction-With sodium bis(2-methoxyethoxy)aluminum-hydride, bromination with triphenylphosphine dibromide and further reaction with triphenylphosphine. Synthesis of compound 8 was achieved by Wittig coupling between propyltriphenylphosphonium bromide (7) and methyl 6-oxohexanoate (1) which was obtained by ozonolysis of cyclohexene. Compound 6 was prepared through the dimethoxy derivative from methyl 8-dioxanyloctanoate-6,7-d2 (4) which was obtained by deuteration of methyl 8-dioxanyloctanoate-6,7-d2(4) which was obtained by deuteration of methyl 8-dloxanyl-6-octenoate (3) with tris(triphenylphosphine)chlororhodium and deuterium gas. Compound 3 was obtained from compound 1 by chain extension with [2-(1,3-dioxan-2-yl)ethyl]triphenylphosphonium bromide (2). Chain extension of 6 with 2 yielded methyl 11-dioxanyl-9-undecenoate-6,7-d2(13). The latter was converted to methyl 12-oxo-9-dodecenoate-6,7-d2 (15) which was treated with 3-hexenyltriphenylphosphonium bromide (16) and butyl lithium to give methyl 9,12,15-octadecatrienoate isomers (17). Geometric isomers formed during each of the Wittig reactions were separated by silver resin chromatography.