Ring-closing metathesis reaction alkene

Suzuki-Miyaura cross-coupling and alkene ring closing metathesis reactions.37... 

In the ring-closing metathesis reaction (RCM), a diene is allowed to undergo intramolecular olefin metathesis to give a cyclic alkene and ethylene the latter is removed to drive the equilibrium forward. The RCM has quickly been adopted as a premier method for preparing macrocyclic natural products. 

As well as ring-closing metathesis reactions, the catalytic asymmetric Homer-Wadsworth-Emmons reaction has been achieved using phase-transfer catalysts including ammonium salt (12.77), with rubidium hydroxide as base. The achiral ketone (12.78) is converted into the alkene (12.79) with reasonable enantioselec-tivity. Currently, the long reaction time is a drawback. ... 

Two independent ring-closing metathesis reactions between two adjacent side chains of 11c gave bicyclic alkene 37 in 46 % yield and with an E Z = 3 1 ratio. Such a relatively low yield was attributed to a co-occurring ADMET-like polymerization, which, although under unfavourable conditions, gave an oligomer product... 

As stated above, olefin metathesis is in principle reversible, because all steps of the catalytic cycle are reversible. In preparatively useful transformations, the equilibrium is shifted to one side. This is most commonly achieved by removal of a volatile alkene, mostly ethene, from the reaction mixture. An obvious and well-established way to classify olefin metathesis reactions is depicted in Scheme 2. Depending on the structure of the olefin, metathesis may occur either inter- or intramolecularly. Intermolecular metathesis of two alkenes is called cross metathesis (CM) (if the two alkenes are identical, as in the case of the Phillips triolefin process, the term self metathesis is sometimes used). The intermolecular metathesis of an a,co-diene leads to polymeric structures and ethene this mode of metathesis is called acyclic diene metathesis (ADMET). Intramolecular metathesis of these substrates gives cycloalkenes and ethene (ring-closing metathesis, RCM) the reverse reaction is the cleavage of a cyclo-... 

With a-monosubstituted ylides the oxidation results in the formation of alkenes (by subsequent Wittig reaction on the intermediate aldehyde). A recent example of such synthesis is found in the preparation of all-(Z)-cyclododecate-traene by oxidation of the appropriate bis-ylide [33]. It must be pointed out that an approach of the same macrocycle based on ring closing metathesis was found ineffective. 

Since the alkene formed in this reaction can further react with other alkenes, many products should be formed in the cross-metathesis (CM). Therefore, in the early days, only ring-closing metathesis (RCM) of diene was investigated. It is known that the reaction is catalyzed by a transition metal. Pioneering work on olefin metathesis was undertaken by Villemin and Tsuji, who reported the synthesis of lactones using alkene metathesis ... 

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