The synthesis of the isomeric components of San Jose scale pheromone — an illustration of a stereospecific synthesis of trisubstituted alkenes

The three isomeric components of the San Jose scale pheromone, 5–7, have been synthesized from a common β-keto ester intermediate. A study of the alkylation of the dianion of methyl acetoacetate with a series of alkylating agents with the same carbon skeleton has been carried out. The trisubstituted alkenes in 5 and 6 have been synthesized stereospecifically via a copper-catalyzed coupling of a methyl Grignard reagent with the E or Z enol phosphate from the alkylated β-keto ester. In the case of the Z enol derivative, the coupling reaction was carried out on the diethyl- and diphenylphosphates, and the enol triflate. The diethyl enol phosphate gave the highest stereoselectivity. The synthetic pheromones were attractive to San Jose scale in the field.[Formula: see text]