A study of the structures and reactions of some methyl substituted unsaturated C18 ester intermediates in the synthesis of a racemic mixture of 10‐methyloctadecanoic acid

Methyl 10‐undecenoate was hydrated to methyl 10‐hydroxyundecanoate using mercury (II) acetate in aqueous tetrahydrofuran (THF). Chromic acid oxidation of methyl 10‐hydroxyundecanoate gave methyl 10‐oxoundecanoate, which was hydrolyzed to 10‐oxoundecanoic acid. Reaction of n‐octyl magnesium bromide complex in THF with 10‐oxoundecanoic acid furnished 10‐hydroxy‐10‐methyloctadecanoic acid after hydrolysis. The latter compound was esterified, and dehydration of methyl 10‐hydroxy‐10‐methyloctadecanoate withp‐toluenesulfonic acid in benzene gave a mixture of unsaturated branched fatty ester intermediates:viz. methyl 10‐methyl‐9‐octadecenoate, 10‐methyl‐10‐octadecenoate and 10‐octyl‐10‐undecenoate. Treatment of the mixture of unsaturated branched fatty ester intermediates with mercury (II) acetate in methanol gave exclusively methyl 10‐methoxy‐10‐methyloctadecanoate. Epoxidation of the same mixture of unsaturated fatty esters withm‐chloroperbenzoic acid provided a mixture of epoxy derivatives: methyl 9,10‐epoxy‐10‐methyloctadecanoate, 10,11‐epoxy‐10‐methyloctadecanoate and 2‐octyl‐oxirane‐nonanoate. Catalytic hydrogenation of the mixture of unsaturated fatty esters gave a racemic mixture of methyl 10‐methyloctadecanoate, which was hydrolyzed to 10‐methyloctadecanoic acid. The structures of the mixture of unsaturated branched fatty ester intermediates and their derivatives were characterized by chemical and spectroscopic analyses.