Synthesis of 19‐cis‐docosenoic, 17‐cis‐eicosenoic and 15‐cis‐octadecenoic acid

Abstract
Large‐scale syntheses of 19‐cis‐docosenoic, 17‐cis‐eicosenoic and 15‐cis‐octadecenoic acid by chain extension of 8‐undecynoic acid via Kolbe's anodic synthesis, as well as by coupling of 1‐butyne with n‐bromoalkanoic acids were found unsuitable. Therefore, 15‐octadecynoic acid was prepared on a large scale from 13‐hexadecyn‐1‐ol by malonic ester coupling. Esterification and reduction with lithium aluminium hydride yielded 15‐octadecyn‐1‐ol. Converting the latter into a methanesulfonate followed by malonic ester synthesis yielded 17‐eicosynoic acid, which, in turn, was converted by the same sequence of reaction steps into 19‐docosynoic acid. Hydrogenation of the acetylenic acids in the presence of Lindlar's catalyst yielded the title compounds.