Chemoselective olefin metathesis transformations mediated by ruthenium complexes.

Over the past decade, ruthenium-mediated metathesis transformations, including polymerization reactions, cross-metathesis, ring-closing metathesis, enyne metathesis, ring-rearrangement metathesis, and also tandem processes, represent one of the most studied families of organic reactions. This has translated into the development of a large number of structurally diverse catalysts. Whereas most of these investigations are focused on determining catalytic performance, only rare examples of studies dealing with chemoselectivity have been reported to date. Usually, variations are observed in product conversions but rarely in product distributions. In this critical review, we provide an overview of the stereochemistry of newly formed C=C bonds either in ring-closing or cross-metathesis as a function of the catalyst structure. A discussion of disparities encountered in macrocyclisation reactions leading (or not) to the formation of dimeric products is also presented. Since distinctive metathesis products could be isolated as a function of the ligand borne by the ruthenium centre--phosphine or N-heterocyclic carbene in the dissymetrization of trienes, enyne metathesis and ring rearrangements, these topics are also discussed (72 references).