Rearrangements olefin metathesis

We will focus on the development of ruthenium-based metathesis precatalysts with enhanced activity and applications to the metathesis of alkenes with nonstandard electronic properties. In the class of molybdenum complexes [7a,g,h] recent research was mainly directed to the development of homochi-ral precatalysts for enantioselective olefin metathesis. This aspect has recently been covered by Schrock and Hoveyda in a short review and will not be discussed here [8h]. In addition, several important special topics have recently been addressed by excellent reviews, e.g., the synthesis of medium-sized rings by RCM [8a], applications of olefin metathesis to carbohydrate chemistry [8b], cross metathesis [8c,d],enyne metathesis [8e,f], ring-rearrangement metathesis [8g], enantioselective metathesis [8h], and applications of metathesis in polymer chemistry (ADMET,ROMP) [8i,j]. Application of olefin metathesis to the total synthesis of complex natural products is covered in the contribution by Mulzer et al. in this volume. 

Olefin metathesis is a rearrangement reaction that includes a transition metal carbene and an olefin. After the catalytic cycle, a new olefin and a new active metal carbene are formed (Scheme 3.5) [90],... 

Another form of olefin metathesis widely used for piperidine formation is ring-rearrangement metathesis (RRM), as shown below. The versatility of this reaction can be seen in its ability... 

Osborn and Green s elegant results are instructive, but their relevance to metathesis must be qualified. Until actual catalytic activity with the respective complexes is demonstrated, it remains uncertain whether this chemistry indeed relates to olefin metathesis. With this qualification in mind, their work in concert is pioneering as it provides the initial experimental backing for a basic reaction wherein an olefin and a metal exclusively may produce the initiating carbene-metal complex by a simple sequence of 7r-complexation followed by a hydride shift, thus forming a 77-allyl-metal hydride entity which then rearranges into a metallocyclobutane via a nucleophilic attack of the hydride on the central atom of the 7r-allyl species ... 

These reactions involve metallate rearrangements , migratory insertion and transition metal-catalysed vinylic substitution reactions. They also perform well in applications in natural product synthesis . Many useful synthetic possibilities arise from application of ring-closing olefin metathesis (RCM) to unsaturated homoaldol products and their derivatives by means of the Grubbs catalyst 3942 4-286 Equation 105 presents some examples. ... 

A. Fiirstner, Olefin Metathesis and Beyond, Angew. Chem. Int. Ed. Engl. 2000, 39, 3012. D. M. Hodgson, F. Y. T. M. Pierand, and P. A. Stupple, Catal3dic Enantioselective Rearrangements and Cycloadditions Involving Ylides from Diazo Compounds, Chem. Soc. Rev. 2001, 30, 50. 

The role of carbenes and metal carbene complexes in transition metal-catalyzed processes is suspected of being quite extensive (61). For example, the role of carbenes in the olefin metathesis reaction as described in the previous section is probably important (55, 60). It is quite possible that the o-v rearrangement is important in these reactions also, but this has not been investigated in detail. 

Olefin isomerization, with Claisen rearrangement, 1, 365 Olefin metathesis with alkyllead, 9, 415 in aqueous media, 1, 834 ESI—MS studies, 1, 812 in high-throughput catalyst discovery, 1, 365 in ionic liquids, 1, 869 for polymerization characteristics, 1, 149 Grubbs catalysts, 1, 151 Schrock catalysis, 1, 150... 

Olefin metathesis. During metathesis, the alkylidene groups of the reactant olefins trade partners and rearrange to give new combinations of alkenes in the products. 

Olefin metathesis is a unique carbon skeleton redistribution in which unsaturated carbon-carbon bonds are rearranged in the presence of metal carbene complexes. With the advent of efficient catalysts, this reaction has emerged as a powerful tool for the formation of C-C bonds in chemistry [1]. Olefin metathesis can be utilized in five types of reactions ring-closing metathesis (RCM), ring-opening metathesis (ROM), respective ringopening metathesis polymerization (ROMP), cross-metathesis (CM), and acyclic diene metathesis polymerization (ADMET). 

There are many sigmatropic rearrangements and all are -selective in open chain compounds but can give Z-alkenes if the structure of the compound demands it. In this way they resemble the McMurry reaction and olefin metathesis. Many such reactions are used to transmit three-dimensional stereochemistry rather than for E/Z control in alkenes. 

Tebbe and co-workers reported the first olefin metatheses between titanocene-methyli-dene and simple terminal olefins [13]. They showed cross-metathesis between isotopically labeled isobutene and methylenecydohexane to be catalyzed by titanocene-methylidene. This process is referred to as degenerate olefin metathesis as it does not yield any new olefin (Scheme 14.6). The intermediate titanacyclobutane has been isolated and characterized [14], and its stability [15] and mechanism of rearrangement [16] have been investigated. 

Olefin metathesis I A chemical reaction in which all of the double bonds in a hydrocarbon molecule are broken and then rearranged. 

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