Synthetic Applications of Alkene Metathesis

The complex WOCI4—Cp2TiMe2 was used for the metathesis of ethyl oleate (51) to give diethyl 9-octadecenedioate (52). Civetone (53) was synthesized by the Dieckmann condensation of this diester, followed by decarboxylation [20], Homometathesis of terminal alkenes is useful, because it yields symmetric internal alkenes and ethylene, which can be removed easily. Metathesis of 10-undecenoate (54) proceeds smoothly to give the diester 55 [20], 

Homometathesis of cyclic alkenes affords larger rings. For example, cyclohex-adecadiene (57) was prepared by liquid-phase metathesis of cyclooctene (56) using WCl5/Et3Al [21], or in the gas phase by short-time contact of cyclooctene to a supported catalyst of Re207 activated with Me4Sn [22], Cyclohexadecenone (58), a muscone-type perfume, is produced commercially from 57 by selective oxidation. 

2 Cross-metathesis using terminal alkenes or ethylene 

Formation of an equilibrium mixture of ethylene and 2-butene by the metathesis of propylene is a convenient process for controlling the relative amounts of ethylene and 

Synthetic reactions via transition metal carbene complexes 

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Reaction of the complex 24 with terminal alkene 25 generates styrene and the real catalytic species 27 via the ruthenacyclobutane 26. The complex 24 is commercially available, active without rigorous exclusion of O2 and water, and has functional group tolerance. Carbonyl alkenation is not observed with the catalysts 22 and 24. Their introduction has enormously accelerated the synthetic applications of alkene metathesis [11]. 

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