Olefin Metathesis in Organic Chemistry

Transition metal catalyzed CC bond formations belong to the most important reactions in organic synthesis. One particularly interesting reaction is olefin metathesis, a metal-catalyzed exchange of alkylidene moieties between alkenes. Olefin metathesis can induce both cleavage and formation of CC double bonds. Special functional groups are not necessary. Although this reaction—which can be catalyzed by numerous transition metals—is used in industry, its potential in organic synthesis was not recognized for many years. The recent abrupt end to this Sleeping-Beauty slumber has several reasons. Novel catalysts can effect the conversion of highly fictionalized and sterically demanding olefins under mild reaction conditions and in high yields. Improved understanding of substrate–catalyst interaction has greatly contributed to the recent establishment of olefin metathesis as a synthetic method. In addition to the preparation of polymers with fine-tuned characteristics, the metathesis today also provides new routes to compounds of low molecular weight. The highly developed ring-closing metathesis has been proven to be key step in the synthesis of a growing number of natural products. At the same time interesting applications can be envisioned for newly developed variants of bimolecular metathesis. Improvements in the selective cross-metathesis of acyclic olefins as well as promising attempts to include alkynes as viable substrates provide for a vivid development of the metathesis chemistry.