Insects find each other to mate by sense of smell, and their chemical signaling pheromones. Adding pheromones to a field can be used as an alternative to pesticides by confusing male insects and preventing mating. While this practice holds promise as an environmentally friendly pest control method, a critical limiting factor is cost. Extracting natural pheromones for production is an effort in futility, and often synthetic processes take many steps. Even if it’s better for the environment, replacing a cheap insecticide in the field with an expensive pheromone will always be an uphill battle.
In an attempt to make a more cost effective pheromone, workers at Materia have reported a process that uses readily available starting materials and an efficient cross metathesis step to produce the major constituent of the Peach Twig Borer pheromone.(1) Starting with symmetrical internal olefins 1 and 2 (individually derived from cross metathesis of the readily available alpha olefins), 0.2 mol% of the 2nd generation Grubbs catalyst generated an equilibration of the mixture. The product was separated by distillation and the starting olefins were recycled.
Granted, this is an equilibrium reaction and a separation is required at the end, but the reaction is run neat, which means the cost and effort of dealing with solvents is avoided. The authors note that using the 2nd generation Grubbs catalyst, when the reaction was performed at 45 °C, up to 17% of olefin isomerization-derived byproducts were formed, but when run at 0 °C, <0.1% of the impurities were observed. The reaction was considerably slower at 0 °C of course, but to avoid a careful separation it was worth it.
(1) Pederson, R. L.; Fellows, I. M.; Ung, T. A.; Ishihara, H.; Hajela, S. P. Adv. Synth. Catal. 2002, 344, 728-735.