Editorial [Hot Topic: Metathesis Reactions in the Synthesis of Biologically Active Compounds and Medicinal Chemistry (Guest Editor: Janine Cossy)]

In the last decades, among the many types of transition-metal catalyzed carbon-carbon bond forming processes, the palladium-catalyzed cross-coupling reactions and the olefin-metathesis reactions have probably played major roles in organic synthesis. Olefin metathesis is now widely considered as one of the most powerful synthetic tools. This reaction, where the carbon-carbon double bond of an alkene is broken and reformed in the presence of an organometallic catalyst, was discoverd 50 years ago and used to synthesize polymers. The elucidation of the mechanistic pathways took at least 20 years and the accepted mechanism of alkene metathesis, proposed by Prof. Chauvin in 1971, invokes metal carbene intermediates as key propagating intermediates in the catalytic cycle. Due to Prof. Schrock and Prof. Grubbs, who designed catalysts which are stable, easily handled, tolerant to most functional groups and commercially available, the alkene metathesis reaction became one of the most powerful carbon-carbon forming reactions currently available to the synthetic chemist and, more and more researchers are employing the metathesis reactions. The synthetic transformations that can be achieved with one catalyst when applied to appropriate substrates is astonishing. Metathesis reactions have a variety of applications including ring-opening metathesis polymerization (ROMP), ring-closing metathesis reactions (RCM), acyclic dienes metathesis polymerization (ADMET), ring-opening metathesis (ROM) and crossmetathesis reaction (CM). The sequential transformation of the alkene obtained in metathesis reactions (domino process) is an attractive application of this synthetic method and can be used in the synthesis of complex molecules in a single catalytic step. Furthermore, tandem metathesis coupled with other alkene reactions (Diels-Alder, Heck...) is a fascinating area of research. In October 2005, the Nobel Committee has recognized the importance and utility of the metathesis reaction as it has awarded Prof. Chauvin (France), Prof. Grubbs (USA) and Prof. Schrock (USA) ≫for the development of the metathesis method in organic synthesis≫. In this review, we do not want to duplicate any of the reviews dealing with metathesis and, rather than presenting an exhaustive coverage of the litterature, all the authors have limited themselves to applications in the field of biologically active relevant molecules (natural and non natural) with emphasis on methods that will be of interest to medicinal chemists. I would like to thank all authors for contributing to this special issue.