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Robert H Grubbs - One of the best experts on this subject based on the ideXlab platform.
Chimia, 2020Co-Authors: Robert H GrubbsAbstract:
The development of highly active ruthenium alkylidene catalysts for olefin Metathesis has enabled new applications in organic synthesis, especially with the cross-Metathesis reaction.
Metathesis and Decomposition of Fischer Carbenes of Cyclometalated Z-Selective Ruthenium Metathesis CatalystsOrganometallics, 2018Co-Authors: Tonia S. Ahmed, Jessica M. Grandner, Buck L. H. Taylor, Myles B. Herbert, Kendall N. Houk, Robert H GrubbsAbstract:
The addition of vinyl ethers to Z-selective, cyclometalated ruthenium Metathesis catalysts generates Fischer carbene complexes. Although Fischer carbenes are usually thought to be Metathesis inactive, we show that Fischer carbenes are Metathesis active under certain circumstances. These species were found to decompose facilely to Ru hydride complexes, as identified by both experiment and computation. Since vinyl ethers are often used to quench Metathesis reactions implementing Ru-based Metathesis catalysts, their decomposition to hydrides can have a deleterious effect on the desired stereochemistry of the olefin product.
tandem olefin Metathesis oxidative cyclization synthesis of tetrahydrofuran diols from simple olefinsJournal of the American Chemical Society, 2016Co-Authors: Peter K Dornan, Robert H GrubbsAbstract:
A tandem olefin Metathesis/oxidative cyclization has been developed to synthesize 2,5-disubstituted tetrahydrofuran (THF) diols in a stereocontrolled fashion from simple olefin precursors. The ruthenium Metathesis catalyst is converted into an oxidation catalyst in the second step and is thus responsible for both catalytic steps. The stereochemistry of the 1,5-diene intermediate can be controlled through the choice of catalyst and the type of Metathesis conducted. This olefin stereochemistry then controls the THF diol stereochemistry through a highly stereospecific oxidative cyclization.
Multiple Olefin Metathesis Polymerization That Combines All Three Olefin Metathesis Transformations: Ring-Opening, Ring-Closing, and Cross MetathesisJournal of the American Chemical Society, 2015Co-Authors: Ki-taek Bang, Robert H Grubbs, Andreas Hess, Tae-lim ChoiAbstract:
We demonstrated tandem ring-opening/ring-closing Metathesis (RO/RCM) polymerization of monomers containing two cyclopentene moieties and postmodification via insertion polymerization. In this system, well-defined polymers were efficiently formed by tandem cascade RO/RCM reaction pathway. Furthermore, these polymers could be transformed to new A,B-alternating copolymers via a sequential cross Metathesis reaction with a diacrylate. Additionally, we demonstrated the concept of multiple olefin Metathesis polymerization in which the dicyclopentene and diacrylate monomers underwent all three olefin Metathesis transformations (ring-opening, ring-closing, and cross Metathesis) in one shot to produce A,B-alternating copolymer.
z selective cross Metathesis with ruthenium catalysts synthetic applications and mechanistic implicationsAngewandte Chemie, 2015Co-Authors: Myles B. Herbert, Robert H GrubbsAbstract:
Olefin cross Metathesis is a particularly powerful transformation that has been exploited extensively for the formation of complex products. Until recently, however, constructing Z-olefins using this methodology was not possible. With the discovery and development of three families of ruthenium-based Z-selective catalysts, the formation of Z-olefins using Metathesis is now not only possible but becoming increasingly prevalent in the literature. In particular, ruthenium complexes containing cyclometalated NHC architectures developed in our group have been shown to catalyze various cross Metathesis reactions with high activity and, in most cases, near perfect selectivity for the Z-isomer. The types of cross Metathesis reactions investigated thus far are presented here and explored in depth.
Siegfried Blechert - One of the best experts on this subject based on the ideXlab platform.
ChemInform, 2004Co-Authors: Stephen J. Connon, Siegfried BlechertAbstract:
The last half decade has been a period of unprecedented development for the range of transition-metal-catalysed alkylidene exchange reactions collectively known as alkene Metathesis. These carbon–carbon bond forming processes have, in a relatively short time, evolved from relative obscurity into a major research area at the forefront of both modern organometallic and synthetic organic chemistry, driven by the rational design of ever more robust and powerful catalytic systems. The advent of modern well-defined catalysts has allowed practitioners to develop alkene Metathesis beyond traditional intramolecular processes into diverse areas such as chemoselective cross-Metathesis, intramolecular and intramolecular enyne Metathesis, domino Metathesis reactions and enantioselective alkene Metathesis, together with applications in solid-phase organic synthesis. The major recent developments in these areas are discussed.
Angewandte Chemie, 2003Co-Authors: Stephen J. Connon, Siegfried BlechertAbstract:
: Among the many types of transition-metal-catalyzed C-C bond-forming reactions, olefin Metathesis has come to the fore in recent years owing to the wide range of transformations that are possible with commercially available and easily handled catalysts. Consequently, olefin Metathesis is now widely considered as one of the most powerful synthetic tools in organic chemistry. Until recently the intermolecular variant of this reaction, cross-Metathesis, had been neglected despite its potential. With the evolution of new catalysts, the selectivity, efficiency, and functional-group compatibility of this reaction have improved to a level that was unimaginable just a few years ago. These advances, together with a better understanding of the mechanism and catalyst-substrate interactions, have brought us to a stage where more and more researchers are employing cross-Metathesis reactions in multistep procedures and in the synthesis of natural products. The recent inclusion of alkynes and hindered bicyclic olefins as viable substrates for bimolecular Metathesis coupling, the discovery of enantioselective cross-Metathesis and cross-Metathesis in water, and the successful marriage of Metathesis and solid-phase organic synthesis has further widened the scope of this versatile reaction.
Angewandte Chemie, 2003Co-Authors: Stephen J. Connon, Siegfried BlechertAbstract:
Among the many types of transition-metal-catalyzed C-C bond-forming reactions, olefin Metathesis has come to the fore in recent years owing to the wide range of transformations that are possible with commercially available and easily handled catalysts. Consequently, olefin Metathesis is now widely considered as one of the most powerful synthetic tools in organic chemistry. Until recently the intermolecular variant of this reaction, cross-Metathesis, had been neglected despite its potential. With the evolution of new catalysts, the selectivity, efficiency, and functional-group compatibility of this reaction have improved to a level that was unimaginable just a few years ago. These advances, together with a better understanding of the mechanism and catalyst-substrate interactions, have brought us to a stage where more and more researchers are employing cross-Metathesis reactions in multistep procedures and in the synthesis of natural products. The recent inclusion of alkynes and hindered bicyclic olefins as viable substrates for bimolecular Metathesis coupling, the discovery of enantioselective cross-Metathesis and cross-Metathesis in water, and the successful marriage of Metathesis and solid-phase organic synthesis has further widened the scope of this versatile reaction.
Tetrahedron Letters, 2000Co-Authors: Simon Gessler, Stefan Randl, Siegfried BlechertAbstract:
Abstract Synthesis and activity in ring closure Metathesis (RCM) and cross Metathesis (CM) of the phosphine-free 1,3-dimesityl-4,5-dihydroimidazole-2-ylidene (IHMes) ruthenium alkoxybenzylidene complex 6 are reported.
Angewandte Chemie, 1997Co-Authors: Matthias Schuster, Siegfried BlechertAbstract:
Transition metal catalyzed CC bond formations belong to the most important reactions in organic synthesis. One particularly interesting reaction is olefin Metathesis, a metal-catalyzed exchange of alkylidene moieties between alkenes. Olefin Metathesis can induce both cleavage and formation of CC double bonds. Special functional groups are not necessary. Although this reaction—which can be catalyzed by numerous transition metals—is used in industry, its potential in organic synthesis was not recognized for many years. The recent abrupt end to this Sleeping-Beauty slumber has several reasons. Novel catalysts can effect the conversion of highly fictionalized and sterically demanding olefins under mild reaction conditions and in high yields. Improved understanding of substrate–catalyst interaction has greatly contributed to the recent establishment of olefin Metathesis as a synthetic method. In addition to the preparation of polymers with fine-tuned characteristics, the Metathesis today also provides new routes to compounds of low molecular weight. The highly developed ring-closing Metathesis has been proven to be key step in the synthesis of a growing number of natural products. At the same time interesting applications can be envisioned for newly developed variants of bimolecular Metathesis. Improvements in the selective cross-Metathesis of acyclic olefins as well as promising attempts to include alkynes as viable substrates provide for a vivid development of the Metathesis chemistry.
Steven T Diver - One of the best experts on this subject based on the ideXlab platform.
Organic Letters, 2005Co-Authors: Anthony J Giessert, Steven T DiverAbstract:
The intermolecular enyne Metathesis between alkynes and styrene derivatives was developed to study electronic effects in enyne Metathesis. A Hammett plot for the overall reaction, catalyst initiati...
Chemical Reviews, 2004Co-Authors: Steven T Diver, Anthony J GiessertAbstract:
Enyne Metathesis is a bond reorganization of an alkene and an alkyne to produce a 1,3-diene (eqs 1 and 2 in Scheme 1). It has been used in both intramolecular and intermolecular applications. Enyne Metathesis bears a mechanistic kinship to alkene Metathesis; however, it is less-studied than alkene Metathesis. The enyne bond reorganization is atom economical and is driven by the enthalpic stability of the conjugated 1,3-diene produced. Stereoselection is often low in intermolecular cases but can be controlled in intramolecular cases. The enyne Metathesis can be catalyzed by metal carbenes or “templated” by metal salts. Many of the same metal carbenes that catalyze alkene Metathesis can be used to promote enyne Metathesis.1 Steven T. Diver grew up in Salt Lake City and attended the University of Utah where he studied with Professor F. G. West as an undergraduate researcher. Diver went on to do his doctoral work with Professor Ed Vedejs at the University of WisconsinsMadison, studying nucleophilic catalysis promoted by phosphines. Diver conducted postdoctoral studies with Professor Stuart Schreiber at Harvard where he used alkene Metathesis to make chemical dimerizers. Presumably this is where he got bitten by the Metathesis bug. Diver began his independent work at the University at Buffalo−The State University of New York (SUNY−Buffalo) in 1997. Diver’s research group is interested in the application of enyne Metathesis to challenging synthetic problems, mechanistic aspects of the enyne Metathesis, and catalyst design employing unusual heterocyclic carbene ligands.
Tetrahedron Letters, 2001Co-Authors: Jason A. Smulik, Steven T DiverAbstract:
Abstract Tandem enyne cross-Metathesis/ring-closing Metathesis between terminal alkynes and 1,5-hexadiene has been demonstrated using the 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene-substituted ruthenium benzylidene complex. Synthesis of 2-substituted 1,3-cyclohexadienes using this one step tandem reaction is reported. In addition, Metathesis products were subjected to [4+2] cycloaddition with N -methylmaleimide yielding the corresponding cycloadducts in one synthetic step.
Amir H Hoveyda - One of the best experts on this subject based on the ideXlab platform.
catalyst controlled stereoselective olefin Metathesis as a principal strategy in multistep synthesis design a concise route to neopeltolideAngewandte Chemie, 2015Co-Authors: Miao Yu, Richard R Schrock, Amir H HoveydaAbstract:
Molybdenum-, tungsten-, and ruthenium-based complexes that control the stereochemical outcome of olefin Metathesis reactions have been recently introduced. However, the complementary nature of these systems through their combined use in multistep complex molecule synthesis has not been illustrated. A concise diastereo- and enantioselective route that furnishes the anti-proliferative natural product neopeltolide is now disclosed. Catalytic transformations are employed to address every stereochemical issue. Among the featured processes are an enantioselective ring-opening/cross-Metathesis promoted by a Mo monoaryloxide pyrrolide (MAP) complex and a macrocyclic ring-closing Metathesis that affords a trisubstituted alkene and is catalyzed by a Mo bis(aryloxide) species. Furthermore, Z-selective cross-Metathesis reactions, facilitated by Mo and Ru complexes, have been employed in the stereoselective synthesis of the acyclic dienyl moiety of the target molecule.
Nature, 2008Co-Authors: Steven J Malcolmson, Simon J Meek, Elizabeth S Sattely, Richard R Schrock, Amir H HoveydaAbstract:
Alkene Metathesis (also called olefin Metathesis or transalkylidenation) is an organic reaction widely used to synthesize products including medicines, polymers and fuels. Its importance was recognized in 2005, when Yves Chauvin, Robert Grubbs and Richard Schrock shared the Nobel prize for work on Metathesis. A new class of molybdenum-based chiral catalyst, capable of initiating alkene Metathesis with exceptional efficiency and enantioselectivity, is reported in this issue. The new catalysts bear a stereogenic metal centre and carry only monodentate ligands. Their effectiveness was demonstrated in an enantioselective synthesis of the Aspidosperma alkaloid, quebrachamine, via a Metathesis reaction that cannot be promoted by any of the previously reported catalysts. This paper discloses a new class of chiral catalysts that initiate olefin Metathesis with exceptional efficiency and enantioselectivity. These new catalysts bear a stereogenic metal centre and carry only monodentate ligands; the molybdenum-based complexes are rendered non-racemic by a stereoselective ligand exchange process involving an enantiomerically pure aryloxide, a class of ligands rarely used in asymmetric catalysis. Discovery of efficient catalysts is one of the most compelling objectives of modern chemistry. Chiral catalysts are in particularly high demand, as they facilitate synthesis of enantiomerically enriched small molecules that are critical to developments in medicine, biology and materials science1. Especially noteworthy are catalysts that promote—with otherwise inaccessible efficiency and selectivity levels—reactions demonstrated to be of great utility in chemical synthesis. Here we report a class of chiral catalysts that initiate alkene Metathesis1 with very high efficiency and enantioselectivity. Such attributes arise from structural fluxionality of the chiral catalysts and the central role that enhanced electronic factors have in the catalytic cycle. The new catalysts have a stereogenic metal centre and carry only monodentate ligands; the molybdenum-based complexes are prepared stereoselectively by a ligand exchange process involving an enantiomerically pure aryloxide, a class of ligands scarcely used in enantioselective catalysis2,3. We demonstrate the application of the new catalysts in an enantioselective synthesis of the Aspidosperma alkaloid, quebrachamine, through an alkene Metathesis reaction that cannot be promoted by any of the previously reported chiral catalysts.
Journal of the American Chemical Society, 2000Co-Authors: Steven B Garber, Jason S Kingsbury, And Brian L Gray, Amir H HoveydaAbstract:
Several highly active, recoverable and recyclable Ru-based Metathesis catalysts are presented. The crystal structure of Ru complex 5, bearing a 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene and styrenyl ether ligand is disclosed. The heterocyclic ligand significantly enhances the catalytic activity, and the styrenyl ether allows for the easy recovery of the Ru complex. Catalyst 5 promotes ring-closing Metathesis (RCM) and the efficient formation of various trisubstituted olefins at ambient temperature in high yield within 2 h; the catalyst is obtained in >95% yield after silica gel chromatography and can be used directly in subsequent reactions. Tetrasubstituted olefins can also be synthesized by RCM reactions catalyzed by 5. In addition, the synthesis and catalytic activities of two dendritic and recyclable Ru-based complexes are disclosed (32 and 33). Examples involving catalytic ring-closing, ring-opening, and cross metatheses are presented where, unlike monomer 5, dendritic 33 can be readily recovered.
Didier Astruc - One of the best experts on this subject based on the ideXlab platform.
Beilstein Journal of Organic Chemistry, 2011Co-Authors: Didier Astruc, Abdou K. Diallo, Sylvain Gatard, Liyuan Liang, Catia Ornelas, Victor Martinez, Denise Méry, Jaime RuizAbstract:
The interplay between olefin Metathesis and dendrimers and other nano systems is addressed in this mini review mostly based on the authors’ own contributions over the last decade. Two subjects are presented and discussed: (i) The catalysis of olefin Metathesis by dendritic nano-catalysts via either covalent attachment (ROMP) or, more usefully, dendrimer encapsulation – ring closing Metathesis (RCM), cross Metathesis (CM), enyne Metathesis reactions (EYM) – for reactions in water without a co-solvent and (ii) construction and functionalization of dendrimers by CM reactions.
Oil & Gas Science and Technology-revue De L Institut Francais Du Petrole, 2007Co-Authors: Didier AstrucAbstract:
Dendrimers containing terminal olefins or ruthenium-benzylidene terminal groups undergo olefin Metathesis reactions (RCM and ROMP types), and essentially results from our group are reviewed here. Dendrimers have been loaded at their periphery with ruthenium-chelating bis-phosphines, which leads to the formation of dendrimer-cored stars by ring-opening-Metathesis polymerization (ROMP). CpFe+-induced perallylation of polymethylaromatics (Cp = η5-C5H5) followed by ring-closing Metathesis (RCM) and/or cross Metathesis (CM) leads to poly-ring, cage, oligomeric and polymeric architectures. In the presence of acrylic acid or metha-crylate, stereospecific CM inhibits oligomerization, and dendritic olefins yield polyacid dendrimers. Finally, cros-metahesis reactions with dendronic acrylate allow dendritic construction and growth.
New Journal of Chemistry, 2005Co-Authors: Didier AstrucAbstract:
Metathesis is one of the most spectacular recent improvements in synthetic strategies for organic synthesis and polymer science. The historical aspects and modern developments of the Metathesis reactions are summarized here. In particular, emphasis is placed on the leading role played by the mechanistic work and proposals of Yves Chauvin and on the history of the efficient catalysts discovered by the groups of R. R. Schrock and R. H. Grubbs. It is pointed out how the Chauvin Metathesis mechanism, with formation of a metallacyclobutane, has been generalized to many organometallic reactions that also involve square intermediates comprising a metal atom. Subsequently, the progressive development of ideas by Schrock and Grubbs during the last three decades has brought the field to the forefront of synthetic chemistry. The quest for efficient Metathesis catalysts is a success story, starting from organometallic mechanisms, that has now invaded the worlds of organic synthesis and polymer science. Indeed, the Schrock’ and Grubbs’ catalysts and their derivatives are now the most efficient catalysts compatible with functional groups for the Metathesis reactions. They considerably shorten synthetic schemes by affording new routes and therefore have changed the way chemists think about synthesis.