Synthesis of muscalure

Muscalure, (Z)-tricos-9-ene, is the sex pheromone of the housefly, and is used in traps to control its populations. Its only structural feature is a Z double bond in the middle of a 23-carbon chain, the ideal target for a Wittig reaction with a non-stabilized ylide.

Tetradecyl bromide and triphenylphosphine give the phosphonium salt, which is deprotonated with a sodium or potassium base (NaHMDS, KHMDS) to avoid lithium salts. The ylide reacts with nonanal at low temperature and forms the Z alkene with good selectivity. If necessary, the small amount of E isomer is removed by chromatography on silver nitrate-impregnated silica gel.