SYNTHESIS OF METHYL (5Z,8Z,11Z,14Z,17E)-EICOSAPENTAENOATE AND METHYL (4Z,7Z,10Z,13Z,16Z,19E)-DOCOSAHEXAENOATE

(3Z,6Z,9Z,12E)-Pentadecatetraenal, a common intermediate in the synthesis of methyl Delta 17t EPA and methyl Delta 19t DHA, was obtained by copper(I)-catalyzed coupling between the Grignard reagent of 1,1-diethoxy-3-butyne and (Z,E)-1-bromo-5,8-undecadien-2-yne followed by semi-hydrogenation of the resulting diendyne. The tetraenic aldehyde was subjected to a Wittig reaction with the ylide of (3-carboxybutyl)triphenylphosphonium bromide or of [6-(2,6,7-trioxabicyclo [2.2.2] octyl)-hex-3-Z-enyl] triphenylphosphonium iodide to give, respectively Delta 17t EPA and the protected Delta 19t DHA in high isomeric purity.