Applications metathesis

Second Generation Recyclable Boomerang Polymer Supported Catalysts for Olefin Metathesis Application of Ardu-engo Carbene Complexes, M. Ahmed, T. Arnauld, a. G.M. Barrett, et at, Synlett 2000, 1007-1009. 

A breakthrough in catalytic metathesis applications was achieved with the second generation of ruthenium-NHC-alkylidene complexes In 54, 55, and 56 NHCs are combined with coordinatively more labile ligands such as phosphines... 

Within the NHCs, increased bulk of the substituents at the nitrogen leads to higher activities in a number of metathesis applications. Thus, the 1,3-mesityl-substituted is advantageous for some applications compared to cyclo-... 

Cross-metathesis applications, 11, 200 enynes, 11, 282 in ethenolysis, 11, 198 Lewis-basic substrates, 11, 193 in one-pot reactions, 11, 197 for reagent synthesis, 11, 188 as simple metathesis reaction, 1, 171 Crotyltributyltins, with aldehydes, 9, 352 Crown ether clathrates, diorganozinc compounds, 2, 335 Crown ether-pendant polysilanes, preparation, 3, 577 Crown-ethers, as hosts, 12, 813... 

Randl, S., and Blechert, S. 2003. In Handbook of Metathesis Applications in Organic Synthesis, vol. 2, ed. Grubbs, R.H. Morlenbach Wiley-VCH. 

Furstner, A., Grela, K. Ring-closing alkyne metathesis application to the stereoselective total synthesis of prostaglandin E2-1,15-lactone. Angew. Chem., Int. Ed. Engl. 2000, 39, 1234-1236. 

Furstner, A., Radkowski, K., Grabowski, J., Wirtz, C., Mynott, R. Ring-Closing Alkyne Metathesis. Application to the Total Synthesis of Sophorolipid Lactone. J. Org. Chem. 2000, 65, 8758-8762. 

Ojima I, Lin S, Inoue T, Miller ML, Borella CP, Geng X, Walsh JJ (2000) Macrocycle Formation by Ring-Closing Metathesis. Application to the Syntheses of Novel Macrocyclic Taxoids. J Am Chem Soc 122 5343... 

Apart from the synthesis of such simple compounds, far more complex entities in the form of high molecular weight polymers reflect the bulk of current metathesis applications. A representative example along these lines is the synthesis of the ring-opened metathesis polymer 22 of norbomene (20) which proceeds as shown in Scheme 7b. Over 45,000 tons of this polymer are produced annually by this, so called, Norsorex process." Among different potential precursors for ROMP, norbomene is particularly easy to convert into polymers because the metathesis relieves the strain of the ring system. Moreover, living norbomene polymer (with the carbene still in place as in 21) can become a scaffold... 

Scheme 7. Industrial olefin metathesis applications the Phillips triolefin process for the production of butene and ethene (a) and the Norsorex process for the ring-opening metathesis polymerization (ROMP) of norbornene (b).

Attachment to the Support via Adsorption onto Inorganic Oxide Supports In 2008, Sels, Jacobs, and coworkers [89] described a simple process, where catalyst 5 was adhered onto silica, and the resulting material was employed in batch and continuous-flow metathesis applications. When both the substrates and reaction media were nonpolar, the system worked effectively however, when polar substrates were introduced, Ru was leached from the material. This observation was further supported when the catalytic system passed a cyclooctene, ROMP-based split-test performed in hexane, yet failed the same experiment in diethyl ether. Likewise, the adhered catalyst performed well in continuous-flow processing of cyclooctene in hexane however, no continuous-flow results were reported using polar substrates. 

The initiation of this complex proceeds via an associative mechanism. As a 14-electron complex, it is susceptible to dimerization, which can limit its initiation rate under certain conditions. Nevertheless, the initiation rates of these complexes are comparable to those of the fastest precatalysts known in ring-closing metathesis applications. 

Catalysts continue to be developed for particular alkene metathesis applications, such as stereoselective cross metathesis. These precatalysts are tasked with selective metathesis and turnover, but must maintain Z-selectivity throughout the reaction. New ruthenium(II) species featuring a Ru-C bond have been recruited for this purpose. In a short time, reactivity gains and improved initiation rates have been achieved in this new area by manipulation of the X-type ligand. 

In addition to the classical diamino carbenes, a few groups also developed cyclic carbene structures with other heteroatoms. The group of Fiirstner was the first to report such a complex (121) for olefin metathesis applications (Figure 11.27). The complex consisted of commercially available l,3,5-triphenyl-4,5-dihydro-lH-l,2,4-triazole-5-ylidene entity as carbene [63]. Although the complex was stable in the crystalline form under Ar for several weeks, it rapidly decomposed in chlorinated solvents. Therefore, although the tested reaction showed high... 

Gallenkamp D, Fiirstner A. Stereoselective Synthesis of E,Z-Configured 1,3-Dienes by Ring-Closing Metathesis. Application to the Total Synthesis of Lactiraidomycin. 

Lin YA, Chalker JM, Floyd N, Bemardes GaJL, Davis BG. Allyl Sulfides Are Privileged Substrates in Aqueous Cross-Metathesis Application to Site-Selective Protein Modification. /Chem Soc. 2008 130(30) 9642—9643. 

Furstner, A., Guth, O., Duffels, A., Seidel, G., Liebl, M., Gabor, B., Mynott, R., Indenylidene complexes of ruthenium optimized synthesis, structure elucidation, and performance as catalysts for olefin metathesis—application to the synthesis of the ADE-ring system of Nakadomarin A, Chem. Eur. J. 2001, 7 4811-4820. 

Urn. J.. Lee. S.S.. and Ying, J.Y. (2010) Mesoporous silica-supported catalysts for metathesis application to a circulating flow reactor. Chem. Commun., 46,806-808,... 

Phosphorus and Sulfur Heterocycles via Ring-closing Metathesis Application in Natural Product Synthesis... 

The functional group tolerance of the ruthenium-based metathesis catalysts has had a tremendous impact on solid-phase organic synthesis. The efficacy of the reaction in solution generally translates directly to solid-phase transformation and its potential has been harnessed in a number of library syntheses, solid-phase syntheses of natural products, or diversity-oriented syntheses. It enables the use of chemically robust alkenes as linkers which can be cleaved by RCM or CM. It, of course, provides new manifolds of diversification in diversity-oriented synthesis as has been elegantly shown in landmark examples by Schreiber and Nelson. Another metathesis application of paramount importance is in peptide chemistry where solid-phase synthesis is omnipresent. The ability to stabilize secondary structures in short peptide motifs and replace pharmacologically unsuitable disulfide bonds or simply restrict the conformation of a peptidic library has already been successfully implemented in a number of important examples. The orthogonality of the metathesis reaction to peptide chemistry provides a really powerful tool in this regard. 

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