Preparative Scale Syntheses of Isomerically Pure (10E,12E,14Z)- and (10E,12E,14E)-Hexadeca-10,12,14-trienals, Sex Pheromone Components of Manduca sexta

Abstract

Short, efficient syntheses yielding products of very high isomeric purity have been developed for (10E,12E,14E)-hexadeca-10,12,14-trienal 1 and the (10E,12E,14Z)-isomer 2, the key pheromone components of the tobacco hornworm moth Manduca sexta. The penultimate (EEZ)-trienol, and aldehyde 1, were freed from isomeric impurities by selective reaction of the impurities with tetracyanoethylene. (EEE)-Aldehyde 2 was prepared by Wittig reaction of (2E,4E)-hexa-2,4-dienyltriphenylphosphonium bromide with 10-acetoxydecanal, deprotection, selective crystallization of the (EEE)-trienol from the resulting mix of isomers, and oxidation. The yield of the (EEE)-trienol was increased further by iodine-catalyzed isomerization of the mix of isomers in the liquor, and further recrystallization.