Insect Pheromone Synthesis: New Methodology

Abstract

The evolution of synthetic logic and methodology in insect pheromones are traced through their development in the boll weevil (Anthonomus grandis) and the pink bollworm (Pectinophora gossypiella). Photochemical synthesis of grandisol (the A. grandis pheromone) was followed by several other very different approaches, each a method of cyclobutane synthesis, e.g., an .alpha.-oxycyclopropyl carbonium ion rearrangement, a 2-step synthesis, cyclization of epoxynitriles, anionic cyclization, the use of lithiocyclopropyl phenyl sulfide, and asymmetric synthesis using a natural product (.beta.-pinene) as starter. In the case of propylure (P. gossypiella pheromone) early synthetic methods were laborious and were succeeded by recent methods which are of considerable technical sophistication, e.g., methods using S and B hetero atoms. These techniques developed in parallel with methodological and conceptual developments in synthetic organic chemistry. Hammel et al (1973) found that while propylure could not be detected in insect extracts, a 1:1 mixture of 7,11-cis,cis- and cis, trans-hexadecadienyl acetates was attractive; this mixture was termed gossyplure. Synthetic methods for gossyplure are discussed. The new conceptual insights and synthetic strategies are considered a testament to the vitality of the field of synthetic organic chemistry.