Stereochemical control of the Wittig reaction of the primary aldehyde, 8-acetoxyoctan-1-al (7) with the nonstabilized alkylide, triphenylphosphonium n-butylide (6), was achieved by controlling the reaction conditions including solvent, temperature and inorganic salts. These conditions can be applied to the direct sythesis of the mixture of (Z)-, and (E)-8-dodecen-1-yl acetate, the sex pheromone of the oriental fruit moth, Grapholitha molesta. The primary aldehyde, 8-acetoxyoctan-1-al (7) was synthesized from 1,8-octanediol which is cheap and readily available.