Olefin methathesis

Several new syntheses of the oxazolidinone ring have been published. Treatment of spoxyurethane 184 with a strong base induced the cyclisation to oxazolidinone 185 which, trough an olefine methathesis afforded 186 . Treatment with iron salt of acyl azide 187 afforded an aziridine, which, upon nucleophilic attack of a chloride ion, was transformed in the final oxazolidinone 188 <00CC287>. 

Hoveyda and co-workers immobilized an olefin metathesis catalyst on monolithic sol-gel and claimed that the catalytic material is easily recyclable. Barrett and co-workersprepared a recyclable boomerang polymer supported catalyst for olefin methathesis by grafting the preformed catalyst to a polystyrene... 

Octene-l-al, 38,62 2-Octenes, 303 2-Octylamine, 554 4-Octyne, 96 2-Octyne-l-ol, 62 4-Octyne-3-one, 96 Olefin inversion, 303-304 Olefin methathesis, 570 Orcinol dimethyl ether, 465 Orcinol monomethyl ether, 465 Osmium tetroxide, 31,575,576 Osmium tetroxide-Potassium chlorate, 361... 

Hoveyda and Schrock developed chiral Mo complexes [145, 146] which have been used successfully as chiral catalysts for enantioselective olefin methathesis. A polymer-supported version of the chiral Mo complex 232 was also prepared. The supported chiral complex delivers appreciable levels of reactivity and excellent enantioselectivity [147] with, in most cases, the chiral catalyst providing as high levels of enantioselectivity as the corresponding homogeneous variant. For example, 236 was obtained in quantitative conversion in 30 min with 98% ee by using the polymeric catalyst 232 (Scheme 3.77). 

Several mechanisms for homogeneous catalytic reactions by transition metal complexes could be even more complicated and consist of more than four steps. Carbonylation of olefins (Figure 5.16) and olefins methathesis over a complex catalysts WC16 + EtAICk, Mo(CO)e/Si02 where n is the oxidation state of Mol,+ Wn+ and n=2-4 (Figure 5.17), can be described by catalytic cycles with 6 intermediates. 

The third class of olefin methathesis in Scheme 21.1 is addition metathesis polymerization (ADMET). This reaction is an alternative method to stitch together olefins into polymers, in this case by a combination of dienes with extrusion of ethylene. Control of molecular weight by the ADMET process is less precise than that by ROMP, but this reaction has been used to make polymers with precise architectures, such as polymers that would be perfectly alternating ethylene-propylene copolymers. ... 

Ivin, K. J. Olefin Methathesis. Academic Press, London, 1983, p. 249. 

Enev and co-workers employed olefin methathesis in their approach to the cw-decalin core of branimycin, an antibiotic." Until their report in 2008, preparations of branimycin almost exclusively employed the use of... 

Numerous studies into the role of metal carbene species as reactive intermediates in homogeneous metal-catalyzed olefin methathesis are generally outside the scope of this chapter. A related report of considerable mechanistic significance is the demonstration that isolable metal carbene complexes such as [W(CO)5(CPhX)] (X = Ph or MeO) can act as initiators of acetylene polymerization. This provides experimental support for an earlier hypothesis that metal-catalyzed polymerizations of acetylenes are propagated as shown in Scheme 2. 

Butilikov, D., Lemcoff, N.G., 2014. Jojoba olefin methathesis a valuable source for bio-renewable materials. Green Chem. 16, 4728-4733. 

An interesting historical account by H. S. Eleuterio about early stages of the discovery of olefin methathesis has appeared Chance favours those... 

TABLE 9 n-vj/-Olefins Produced in the Isomeriza-tion-Methathesis Step of the Shell Process ... 

Scheme 3 Mechanism of the ring-expansion methathesis polymerization of cyclic olefins.

In addition to the metathesis of olefins, metathesis between an olefin and an aUcyne and metathesis between two alkynes are known and can be synthetically valuable. The metathesis between an olefin and an alkyne is called en)me metathesis, and enyne methathesis is the final class of reaction involving an alkene shown in Scheme 21.1. This process combines an olefin with an alkyne to generate a diene. The thermodynamic driving force for this process is created by tire generation of a new carbon-carbon single bond from the cleavage of one of the ir-bonds in an alkyne. 

Carbene cations such as FeCH2 and CoCH activate alkanes and cycloalkanes, and in the case of olefins both their methathesis as well as activation takes place as inferred from the hydrogen evolution. 

K. J. Ivin and I. C. Mol, Olefin Metathesis and Methathesis Polymerization, Academic Press, San Diego, 1996. 

Finally, despite the plethora of reports providing evidence for the one carbene exchange mechanism, in certain circumstances cyclobutanes can be converted quantitatively into diolefins and, of greater importance, two non-conjugated olefinic groups (31) can be converted into a cyclobutane (32) almost quantitatively by the methathesis catalyst PhWCls-AlCla. This suggests that the carbene mechanism is not a unique pathway for olefin disproportionation and that in some circumstances cyclobutane intermediates may be formed. 

These secondary metathesis reactions of course may also affect the microstructure of the polymers, e.g., the fraction of cis double bonds [275,283]. The extend of these reactions depends in particular on steric factors and the activity of the applied catalyst. The sterical shielding of polynorbomenes backbone by the 5-membered rings is probably responsible for the low reactivity in degradation reactions via cross methathesis with acyclic olefins, too [276]. 

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