Sex pheromone candidates with a conjugated triene system: Synthesis and chemical characterization

Sex pheromone candidates with a conjugated triene system, 8,10,12-, 9,11,13- and 11,13,15-hexadecatrienyl acetates (double bond positional isomers of theGlyphodes pyloalis pheromone, 10,12,14-triene) were synthesized by introducing anE configuration stereospecifically to two of three double bonds and rather nonspecifically to another double bond, so as to obtain two geometrical isomers;E,E,E andE,E,Z orE,Z,E isomers. The two geometrical isomers of each triene acetate were separated on a reverse-phase HPLC column and characterized by(1)H NMR analysis. The(13)C NMR signals in the olefinic region of each isomer were assigned by two-dimensional NMR techniques and also by an empirical rule based on the changes of the chemical shifts by converting the configuration. Based on the assignments, substituent parameters for calculating the chemical shifts of 1,6-dialkyl conjugated trienes were generated. Electron impact mass spectrometry showed characteristic fragment ions that enabled the double bond positional isomers to be distinguished from each other.