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Recent Developments in Olefin Cross-Metathesis - …

T1 - Catalytic Z-selective olefin cross-metathesis for natural product synthesis

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» Topic: Grubbs Olefin Metathesis Review – 439880

Alkenes are found in many biologically active molecules, and there are a large number of chemical transformations in which alkenes act as the reactants or products (or both) of the reaction. Many alkenes exist as either the E or the higher-energy Z stereoisomer. Catalytic procedures for the stereoselective formation of alkenes are valuable, yet methods enabling the synthesis of 1,2-disubstituted Z alkenes are scarce. Here we report catalytic Z-selective cross-metathesis reactions of terminal enol ethers, which have not been reported previously, and of allylic amides, used until now only in E-selective processes. The corresponding disubstituted alkenes are formed in up to >98% Z selectivity and 97% yield. These transformations, promoted by catalysts that contain the highly abundant and inexpensive metal molybdenum, are amenable to gram-scale operations. Use of reduced pressure is introduced as a simple and effective strategy for achieving high stereoselectivity. The utility of this method is demonstrated by its use in syntheses of an anti-oxidant plasmalogen phospholipid, found in electrically active tissues and implicated in Alzheimers disease, and the potent immunostimulant KRN7000.

24/04/2017 · Olefin cross metathesis and ring-closing metathesis in polymer ..
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Efficiency in olefin cross-metathesis reactions is affected upon reducing the steric bulk of N-heterocyclic carbene ligands of ruthenium-based catalysts. For the formation of disubstituted olefins containing one or more allylic substituents, the catalyst bearing N-toiyl groups is more efficient than the corresponding N-mesityl catalyst. In contrast, the formation of trisubstituted olefins is more efficient using the W-mesitylcontaining catalyst. A hypothesis to explain this dichotomy is described.

Grubbs Olefin Metathesis Review

[09.30] Reactivity of Vinyl-Terminated Self-Assembled Monolayers on Gold: Olefin Cross-Metathesis Reactions.
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Although metathesis-type reactions represent one of the most valuable strategies in modern organic synthesis, making this highly valuable tool more accessible and practical for routine use still remains a challenge. Ruthenium-based catalysts have been at the centre of recent advancements making possible their use in air, moreover these catalysts are becoming more and more stable, efficient and economically friendly with time. With the current development directed towards air and moisture stability and high performance, there is no doubt that more reports will push these reactivity/tolerance limits even further. As seen in this review, conducting metathesis-type reactions in air, in the presence of water and under high temperature has become more concrete, with several groups leading the charge [,].

In 2002, Hoveyda et al. reported the Hoveyda–Grubbs’ 2nd generation type catalyst 36 () []: Complex 36, bearing an unsymmetrical and chiral NHC, was active in the asymmetric ring-opening cross-metathesis (RO/CM) in air using undistilled solvents, and yielded products with high enantiomeric excess (ee). The results where comparable to previously reported results for molybdenum-catalyzed systems [], although the latter was used under inert conditions.

The Olefin Metathesis Reaction Chem 215 Myers Reviews: Nicolaou, K

Bannister* Translational Research Institute.A General Model for Selectivity in Olefin Cross Metathesis Arnab K.
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Specifically, the Columbia team treated ruthenium films with 4-bromophenyldiazomethane--and separately with trimethylsilyldiazomethane--to prepare two types of derivatized surfaces featuring molecules that are multiply bonded to ruthenium. Then in separate reactions, each type of derivatized surface is converted to the other type using olefinic reagents in cross-metathesis reactions. The team reports that the products remain stable upon exposure to oxygen, moisture, and various solvents.

AB - Alkenes are found in many biologically active molecules, and there are a large number of chemical transformations in which alkenes act as the reactants or products (or both) of the reaction. Many alkenes exist as either the E or the higher-energy Z stereoisomer. Catalytic procedures for the stereoselective formation of alkenes are valuable, yet methods enabling the synthesis of 1,2-disubstituted Z alkenes are scarce. Here we report catalytic Z-selective cross-metathesis reactions of terminal enol ethers, which have not been reported previously, and of allylic amides, used until now only in E-selective processes. The corresponding disubstituted alkenes are formed in up to >98% Z selectivity and 97% yield. These transformations, promoted by catalysts that contain the highly abundant and inexpensive metal molybdenum, are amenable to gram-scale operations. Use of reduced pressure is introduced as a simple and effective strategy for achieving high stereoselectivity. The utility of this method is demonstrated by its use in syntheses of an anti-oxidant plasmalogen phospholipid, found in electrically active tissues and implicated in Alzheimers disease, and the potent immunostimulant KRN7000.

29/04/2003 · Review Recent Developments in Olefin Cross-Metathesis
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Application of Olefin Cross-Metathesis to the Synthesis …

Side-chain linked dimers of Ser, Cys and Tyr were obtained by cross-metathesis, while olefin installation at the N- and C-terminus led to dimers of Arg and Phe (or Tic), respectively.

Olefin Cross‐Metathesis: A Powerful Tool for …

Kotohiro Nomura accomplished his master degree from University of Tokyo in 1988 (Institute of Industrial Science, Prof. Y. Saito) and joined as a research scientist in the Organic Synthesis Research Laboratory, Sumitomo Chemical Company, Ltd. He received his Ph.D. degree in 1993 from Osaka University (by thesis submission, Prof. N. Sonoda) and joined the group of Prof. R. R. Schrock (Massachusetts Institute of Technology) as a postdoctoral fellow for two years. He then returned to Sumitomo as a research scientist in the Petrochemical Research Laboratory and moved to Nara Institute of Science and Technology (NAIST) as an Associate Professor in 1998 on the occasion of establishment of the Graduate School of Materials Science. He recently moved to the Laboratory of Organic Chemistry, Department of Chemistry, Tokyo Metropolitan University (TMU) as a full professor (April 2010). His recent research projects especially focus on design of molecular catalysts for precise olefin polymerization, metathesis reactions, and chemospecific organic transformations. He received The CSJ Award for Young Chemists in Technical Development from The Chemical Society of Japan in 1996 and The Society Award (Chemical & Engineering) from Catalysis Society of Japan in 2001. He has coauthored over 170 publications including review articles and book chapters.

New Approaches to Olefin Cross-Metathesis Helen E

N2 - Alkenes are found in many biologically active molecules, and there are a large number of chemical transformations in which alkenes act as the reactants or products (or both) of the reaction. Many alkenes exist as either the E or the higher-energy Z stereoisomer. Catalytic procedures for the stereoselective formation of alkenes are valuable, yet methods enabling the synthesis of 1,2-disubstituted Z alkenes are scarce. Here we report catalytic Z-selective cross-metathesis reactions of terminal enol ethers, which have not been reported previously, and of allylic amides, used until now only in E-selective processes. The corresponding disubstituted alkenes are formed in up to >98% Z selectivity and 97% yield. These transformations, promoted by catalysts that contain the highly abundant and inexpensive metal molybdenum, are amenable to gram-scale operations. Use of reduced pressure is introduced as a simple and effective strategy for achieving high stereoselectivity. The utility of this method is demonstrated by its use in syntheses of an anti-oxidant plasmalogen phospholipid, found in electrically active tissues and implicated in Alzheimers disease, and the potent immunostimulant KRN7000.

Ring-opening Metathesis Polymerization

The cross-metathesis of polynorbornene and polyoctenamer in d-chloroform mediated by the 1 st generation Grubbs catalyst Cl 2 (PCy 3) 2 Ru=CHPh.• Cross metathesis (CM) Classes of olefin metathesis.

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