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Ruthenium-Catalyzed Olefin Metathesis Double-Bond ..

(2005), Ruthenium-Catalyzed Olefin Metathesis Double-Bond Isomerization Sequence

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Ring Closing Metathesis - Organic Chemistry Portal

A novel ruthenium-catalyzed tandem ring-closing metathesis (RCM) double-bond isomerization reaction is described in this paper. The utility of this method for the efficient syntheses of five-, six-, and seven-membered cyclic enol ethers is demonstrated. It relies on the conversion of a metathesis-active ruthenium carbene species to an isomerization-active ruthenium−hydride species in situ. This conversion is achieved by using various additives. Scope and limitations of the different protocols are discussed, and some mechanistic considerations based on 31P and 1H NMR spectroscopic studies are presented.

Ruthenium-catalyzed olefin metathesis double-bond isomerization sequence

Whereas a number of highly -selective ruthenium-based olefin metathesis catalysts bearing N-heterocyclic carbene ligands have been reported in recent years, -selectivity has so far been difficult to achieve for phosphine-based catalysts. Guided by predictive density functional theory (DFT) calculations, we have developed phosphine-based ruthenium olefin metathesis catalysts giving 70–95% of the -isomer product in homocoupling of terminal alkenes such as allylbenzene, 1-octene, allyl acetate, and 2-allyloxyethanol. Starting from a moderately selective catalyst, [P(Cy)3](-S-2,4,6-Ph-C6H2)ClRu(═CH--OPrC6H4) (4, Cy = cyclohexyl, Pr = isopropyl), obtained by substituting a chloride of the Hoveyda–Grubbs first-generation catalyst with 2,4,6-triphenylbenzenethiolate, we moved on to replace Cl and PCy3 by chelating, anionic phosphine ligands. Such ligands increase selectivity by limiting rotation around the P–Ru bond and by specifically directing the steric bulk of the phosphine substituents toward the selectivity-inducing thiolate ligand. In particular, DFT calculations predicted that -(dialkylphosphino)phenolate ligands should improve selectivity and activity compared to 4. The most promising of these compounds (8b), based on the -(di--butylphosphino)phenolate ligand, directs the two P-bonded -butyl substituents toward the 2,4,6-triphenylbenzenethiolate and has little steric hindrance to the thiolate. This compound metathesizes terminal olefins such as allylbenzene and 1-octene with -selectivities above 80% and allylacetate above 90%. Although these phosphine-based ruthenium monothiolate catalysts in general achieve somewhat lower activities and -selectivities than their second-generation counterparts, they also offer examples giving less substrate and product isomerization and thus higher yields.

Olefin Ring Closing Metathesis and Hydrosilylation ..

In this regard, reaction conditions have been identified that allow for a tandem ring-closing metathesis-olefin isomerization sequence catalyzed by a common ruthenium precursor.

Tandem reactions that proceed with a single metal catalyst precursor offer novel opportunities for developing efficient new reaction sequences. In this regard, reaction conditions have been identified that allows for a tandem ring-closing metathesis−olefin isomerization sequence catalyzed by a common ruthenium precursor. Specifically, the tandem process generates cyclic enol ethers from a variety of readily available acyclic dienes in a single reaction vessel using Grubbs' ruthenium alkylidene.

Nonmetathesis Heterocycle Formation by Ruthenium-Catalyzed ..

Ruthenium catalysts.We have made several contributions to this research field and have already reported several nonmetathesis reactions, i.e., isomerizations of terminal olefins, cycloisomerizations, and one-pot metathesis and subsequent nonmetathesis reactions to give novel heterocyclic dyes.Allenamides are important functional groups in organic synthesis, and many allenamides reactions have been developed. Allenamides reactions using organometallic catalysts have been reported, but nonmetathesis reactions with ruthenium carbene catalysts are limited to isomerizations and cycloisomerizations (see eqs 1 and 2 in ). These reactions both proceed via a ruthenium hydride species with a nitrogen-containing heterocyclic carbene ligand generated from a Grubbs II catalyst.

A novel ruthenium-catalyzed tandem ring-closing metathesis (RCM) double-bond isomerization reaction is described in this paper. The utility of this method for the efficient syntheses of five-, six-, and seven-membered cyclic enol ethers is demonstrated. It relies on the conversion of a metathesis-active ruthenium carbene species to an isomerization-active ruthenium−hydride species in situ. This conversion is achieved by using various additives. Scope and limitations of the different protocols are discussed, and some mechanistic considerations based on 31P and 1H NMR spectroscopic studies are presented.

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  • Ruthenium-catalyzed tandem ring closing metathesis …

    An Olefin Metathesis/Double Bond Isomerization Sequence Catalyzed by an In Situ Generated Ruthenium Hydride Species

  • Ruthenium-catalyzed tandem ring closing metathesis ..

    Organic Chemistry

  • field of ruthenium-catalyzed olefin metathesis ..

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