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Ring Closing Metathesis Reaction Mechanism

N2 - A tandem cross metathesis (CM)-ring-closing metathesis (RCM) sequence to form cyclic siloxanes is reported. This new enyne metathesis platform expands the scope and utility of the regio- and stereoselective cross metathesis reaction between silylated alkynes and terminal alkenes. The initial cross metathesis was directed to occur on the alkyne by employing sterically hindered mono-, di-, and trisubstituted alkenes tethered to the alkyne via silyl ether. The regio- and stereoselectivity feature of the initial CM step in this tandem CM-RCM process is identical to that of the CM reactions of silylated alkynes and alkenes. This tandem sequence provides both synthetically useful silylated 1,3-diene building blocks and insights into the reaction mechanism of the enyne metathesis reaction.

10/09/2014 · Olefin Metathesis: Reaction, Mechanism, Structure - Duration: 6:46

Ruthenium-based catalysts for olefin metathesis display high activity in the presence of common functional groups and have been utilized in a variety of chemical disciplines. This thesis describes the development of new catalysts with superior properties and mechanistic studies directed at understanding the factors governing catalyst activity and selectivity. Chapter 2 describes the preparation of acid-activated olefin metathesis catalysts containing acetylacetonate (acac)-type ligands. The effect of ligand structure and the exogenous acid on catalytic activity was examined. The acid-activated catalysts were also combined with a photoacid generator (PAG), which resulted in a highly active system for photo-activated olefin metathesis. Chapter 3 details the incorporation of mesoionic carbenes (MICs) into ruthenium metathesis catalysts. The activity of these catalysts in several metathesis assays was measured and correlated to their initiation rates. The protonolysis of a Ru-MIC bond and the incorporation of this reaction into an acid-activated catalyst are also described. Chapter 4 explores the relationship between catalyst structure and degenerate metathesis. A ring-closing metathesis assay was used to measure the preference of different catalysts for productive or degenerate metathesis. The relationship between degenerate metathesis and reactions such as ethenolysis is also discussed. Chapter 5 describes the study of ruthenacyclobutanes formed from the degenerate metathesis selective catalysts presented in Chapter 4. The rates of various chemical exchange processes were measured and correlated to catalyst structure. Kinetic parameters for the rate-limiting step in ring-closing metathesis were also measured and used to rationalize the differences in productive/degenerate selectivity for various catalysts. Chapter 6 details the preparation and study of C-H-activated ruthenium catalysts for Z-selective olefin metathesis. Ligand effects on catalyst activity and selectivity are explored along with the application of these catalysts in Z-selective cross-metathesis and ring-opening metathesis polymerization.

towards the study of the enyne metathesis reaction mechanism

A., On the mechanism of the reaction of organic azides with transition metals: Evidence for triplet nitrene capture.

This insertion was proposed as a way to stop metathesis reactions for kineticanalysis to study reaction mechanism, but it has evolved into a practicalprocedure to both stop a metathesis reaction and to facilitate purification ofthe organic products.

We will interpret these data in terms of our ongoing syntheticstudies in ene-yne metathesis, and collaterally use this knowledge to developnew applications of the ene-yne metathesis.In year two, we have also employed our mechanisticknowledge of the enyne metathesis to develop three new reactions.

Ring-opening Metathesis Polymerization

connect to download. Get pdf. Relay cross metathesis reactions of vinylphosphonates

A tandem cross metathesis (CM)-ring-closing metathesis (RCM) sequence to form cyclic siloxanes is reported. This new enyne metathesis platform expands the scope and utility of the regio- and stereoselective cross metathesis reaction between silylated alkynes and terminal alkenes. The initial cross metathesis was directed to occur on the alkyne by employing sterically hindered mono-, di-, and trisubstituted alkenes tethered to the alkyne via silyl ether. The regio- and stereoselectivity feature of the initial CM step in this tandem CM-RCM process is identical to that of the CM reactions of silylated alkynes and alkenes. This tandem sequence provides both synthetically useful silylated 1,3-diene building blocks and insights into the reaction mechanism of the enyne metathesis reaction.

AB - A tandem cross metathesis (CM)-ring-closing metathesis (RCM) sequence to form cyclic siloxanes is reported. This new enyne metathesis platform expands the scope and utility of the regio- and stereoselective cross metathesis reaction between silylated alkynes and terminal alkenes. The initial cross metathesis was directed to occur on the alkyne by employing sterically hindered mono-, di-, and trisubstituted alkenes tethered to the alkyne via silyl ether. The regio- and stereoselectivity feature of the initial CM step in this tandem CM-RCM process is identical to that of the CM reactions of silylated alkynes and alkenes. This tandem sequence provides both synthetically useful silylated 1,3-diene building blocks and insights into the reaction mechanism of the enyne metathesis reaction.

03/01/2018 · The power of this cross-metathesis reaction is demonstrated by the concise ..
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reaction - Dizionario inglese-italiano WordReference

Olefin metathesis reactions with 3E-1,3-dienes using Z-selective cyclometalated ruthenium benzylidene catalysts are described. In particular, a procedure for employing 3E-1,3-dienes in Z-selective homodimerization and cross-metathesis with terminal alkenes is detailed. The reaction takes advantage of the pronounced chemoselectivity of a recently reported ruthenium-based catalyst containing a cyclometalated NHC ligand for terminal alkenes in the presence of internal E-alkenes. A wide array of commonly encountered functional groups can be tolerated, and only a small excess (1.5 equiv) of the diene coupling partner is required to achieve high yields of the desired internal E,Z-diene cross-metathesis product. Computational studies have been performed to elucidate the reaction mechanism. The computations are consistent with a diene-first pathway. The reaction can be used to quickly assemble structurally complex targets. The power of this cross-metathesis reaction is demonstrated by the concise syntheses of two insect pheromones.

Name Reactions - Organic Chemistry Portal

Last, our evolving mechanistic knowledge has resulted in thedevelopment of synthetic methods employing enyne metathesis for ring expandingreactions and for difficult cross enyne metathesis.

Wittig Reaction - Organic Chemistry Portal

Secondary metathesis reactions (controlled by catalyst choice and reaction conditions) also affect the product distribution. Recoordination of an alkene on the growing polymer chain with the catalyst can lead to cyclic oligomers through a ring-closing metathesis reaction (“backbiting”). Chain transfer (cross metathesis) between a growing polymer unit and an adjacent polymer alkene also leads to broadened molecular weights. Chain transfer can also be used to improve processability of the resulting polymer – addition of an acyclic olefin (chain-transfer agent) can limit chain molecular weights and introduce terminal functional groups.

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