A convenient route for synthesis of 2-isopropyliden-5-methyl-4-hexen-1-yl butyrate, the sex pheromone of Planococcus kraunhiae (Hemiptera: Pseudococcidae), by use of β,γ to α,β double-bond migration in an unsaturated aldehyde

The Japanese mealybug Planococcus kraunhiae (Kuwana) is an important pest which spoils many kinds of fruit in Japan. Because conventional application of insecticides is often ineffective, alternative strategies are being investigated for management of this pest. Recent studies revealed that a pheromone-based technique which interferes with sexual communication, i.e. mating disruption, was promising. However, mating disruption usually requires a substantial amount of a pheromone. I therefore developed a new and convenient route for synthesis of the P. kraunhiae pheromone, 2-isopropyliden-5-methyl-4-hexen-1-yl butyrate (fujikonyl butyrate). First, a commercially available isomer of fujikonol, 2-isopropenyl-5-methyl-4-hexen-1-ol (lavandulol), was oxidized, furnishing the corresponding aldehyde (lavandulal). The β,γ double bond of lavandulal smoothly migrated to the α,β position in the presence of acids, and as a consequence, the corresponding aldehyde of fujikonol (fujikonal) was obtained. Fujikonal was then reduced to fujikonol, which was esterified with butyric acid to give the pheromone of P. kraunhiae. All the reactions were accomplished under very mild conditions (room temperature to 50 °C) with good yields. Moreover, only small amounts of by-products were generated. The synthetic pheromone obtained by this method can be used as a mating disruptant.