Synthesis of (7Z,9Z)-dodecadienyi acetate, a component of sex pheromones of the leafrollersEpinotia andEucosma, using conjugated diynols

Abstract

Two analogous routes to the title pheromones were elaborated based on organocuprate cross-coupling ofZ,Z-dienic electrophiles, (2Z,4Z)-1-acetoxy-2,4-heptadiene (6) and (3Z,5Z)-1-bromoctadiene (8), with ω-tert-butoxy-1-chloropentane and -butane, respectively. Optimal conditions for the reduction of 2,4-heptadiyn-1-ol and 3,5-octadiyn-1-ol to the respectiveZ,Z-alkadienols as precursors for the electrophiles were found. Treatment of diynols with activated zinc in aqueous alcohol provided high geometrical purity of the product (≥94 %). In both cases, copper-catalyzed cross-coupling afforded 1-tert-butoxy-7,9-dodecadiene (four stereoisomers), acetolysis of which gave the target pheromone contaminated by stereoisomers. In the case of allylic electrophile6, the reaction occurred with the loss of the initial configurational purity, whereas the use of homoallylic bromide8 ensured almost complete retention of the configuration of the double bonds and obtaining the target pheromone of 87 % configurational purity.