(Z)-13-Eicosen-10-one (1), one of the active components of the female pheromone of the peach fruit moth, Carposina niponensis Walsingham, was synthesized from 2-nonanone, succinic anhydride, and n-nonyllithium. The key step involves the preparation of 13-eicosyn-10-one from an epoxyketone via Eschenmoser cleavage.