Syntheses and NMR Analyses of Eight Geometrical Isomers of 10,12,14-Hexadecatrienyl Acetate, Sex Pheromone Candidates of the Mulberry Pyralid

Abstract

Eight geometrical isomers of 10,12,14-hexadecatrienyl acetate, female sex pheromone candidates of the mulberry pyralid (Glyphodes pyloalis Walker), were synthesized by six routes. Each route consisted of reactions by which two of three double bonds were introduced stereospecifically and another rather nonspecifically, giving mainly two geometrical isomers, which were analyzed by 2D-NMR after separating by reversed-phase HPLC or by a reaction with tetracyanoethylene. The signals of the olefinic protons and carbons of each geometrical isomer were assigned by COSY spectra and by C-H COSY spectra, respectively, in addition to the signals of the allylic protons and carbons, and its chemical structure was revealed by the values of their chemical shifts and coupling constants. Furthermore, a new empirical rule concerning the chemical shift changes of these carbons by converting the configuration of the conjugated triene system is suggested.