Synthesis of Pheromones: Highlights from 2002-2004

Abstract

This review summarizes the synthesis of pheromones published in the triennium 2002-2004. The syntheses of a total of 66 pheromone (65 from insects, 1 from a crustacean species), belonging to 9 different structural cate- gories, are presented in schemes. New methodologies, but also well-known reactions have been employed to achieve the (in many cases stereoselective) synthesis of the compounds. Since its very beginnings in the mid 19th century, or- ganic chemistry has made advances unimaginable to the early pioneers of the field. Among the experimental key techniques contributing to these advances are chromatogra- phy, which made possible the separation of complex mix- tures, and spectroscopic (UV, IR, NMR) and mass spectro- metric methods, giving organic chemists powerful tools for the structure determination of organic compounds. This, in turn, stimulated research in organic synthesis, as products and by-products of reactions could be easily isolated and characterized. As once stated by Meinwald, Organic chem- istry blossomed into a self-contained, inward-looking sci- ence, bringing order and understanding to the synthesis and reactions of millions of compounds (1). This order and un- derstanding allowed the development of countless reactions of carbon-carbon bond formation or modification of func- tional groups, applicable to all classes of organic molecules, which would later eventually be modified or improved, e.g. in terms of scope, yields, reaction conditions, or stereo- chemical selectivities. Research in chemical communication has been profiting from these decade-lasting and ongoing efforts, as the synthesis of pheromones is of great importance in the process of identifying these chemical messengers. Moreover, a sort of mutualism has been evolving, as many new synthetic methods have been developped with the ex- plicit aim to improve the synthetic route towards a phero- mone. Pheromones are which are produced and lib- erated by an individual, provocing a behavioural or physio- logical response in another individual of the same species. As pheromones are usually produced in minute amounts, thus preventing crystallographic or extensive NMR experi- ments, their independent synthesis is required to confirm the identification and to establish the absolute configuration in case of chiral compounds. Furthermore, chemical synthesis of pheromones provides the amounts necessary for the evaluation of their biological activity in the laboratory or in the field.