Ring-closing Metathesis Of Dienes Research Articles

Stereoselective Synthesis of Medium-Sized Cyclic Ethers by Sequential Ring-Closing Metathesis and Tsuji-Trost Allylation.

Fully functionalized medium-sized cyclic ethers, of the type found in fused polyether natural products, have been prepared by sequential ring-closing diene metathesis, conversion of the resulting cyclic enone into an allylic enol carbonate, and Tsuji-Trost allylation using a chiral palladium complex. Very high levels of diastereocontrol, favoring the diastereomer in which there is a cis relationship between the allyl group at C-2 of the medium-ring ether and the substituent at C-7/C-8, are obtained in cases where catalyst control and substrate control are matched.

A partially serendipitous discovery of thermo-switchable ruthenium olefin metathesis initiator that seem to be well suited for ROMP of monomers bearing vinyl pendant groups

A latent Ru olefin metathesis catalyst bearing a chelating ligand with an azoxybenzene fragment was obtained and characterized. The complex was inactive in the ring closing metathesis (RCM) reaction of a standard test diene: diethyl diallylmalonate at room temperature but can be subsequently activated by elevated temperature (up to 100 °C). The lack of activity of this azoxy catalyst in RCM of dienes containing terminal C-C double bonds at room temperature and high activity in ring opening metathesis polymerization (ROMP) of bicyclo [2.2.1]hept-2-ene (norbornene, NBE) permitted the ROMP of the challenging monomer: 5-vinyl-2-norbornene yielding soluble polymers with cyclopentenylenevinylene chains with vinyl pendant groups.

ChemInform Abstract: Synthesis of 5,6‐Dihydro‐2H‐pyran‐2‐ones (Microreview)

AbstractReview: [19 refs.

Cascade Metathesis Reactions for the Synthesis of Taxane and Isotaxane Derivatives.

Tricyclic isotaxane and taxane derivatives have been synthesized by a very efficient cascade ring‐closing dienyne metathesis (RCDEYM) reaction, which formed the A and B rings in one operation. When the alkyne is present at C13 (with no neighboring gem‐dimethyl group), the RCEDYM reaction leads to 14,15‐isotaxanes 16 a,b and 18 b with the gem‐dimethyl group on the A ring. If the alkyne is at the C11 position (and thus flanked by a gem‐dimethyl group), RCEDYM reaction only proceeds in the presence of a trisubstituted olefin at C13, which disfavors the competing diene ring‐closing metathesis reaction, to give the tricyclic core of Taxol 44.

Synthesis of 5,6-dihydro-2H-pyran-2-ones (microreview)

5,6-Dihydro-2H-pyran-2-ones constitute an important class of heterocyclic compounds which also may be considered as α,β-unsaturated δ-lactones. These types of heterocycles have shown a wide range of biological and pharmacological activities including human antitumor,1 , 2 antifungal,3 , 5 antimicrobial,4 anti-inflammatory,4 antistress,4 antibiotic,5antituberculosis,6 antiparasitic,6 antiviral;7 5,6-dihydro-2Hpyran-2-ones are also known as the inducer of a colony stimulating factor in bone marrow stromal cells.5 All this made 5,6-dihydro-2H-pyran-2-ones more attractive both for chemists and pharmacologists. For example, (R)-rugulactone which was firstly reported in 2009 by Cardellina and coworkers possess interesting anticancer properties.2 In addition, 5,6-dihydro-2H-pyran-2-ones as chemical intermediates have widely been applied to the synthesis of numerous organic compounds including heterocycles.8 Nowadays, there are several synthetic routes to the preparation of these heterocycles including intramolecular cyclization, N-heterocyclic carbeneprecatalyst (NHC-precatalyst) reaction of enals and ketones, dicobaltoctacarbonyl-mediated tandem (5+1)/(4+2) cycloaddition, ring-closing metathesis of dienes containing carboxylate group by Grubbs II catalyst, (3+2) cycloaddition reaction, condensation reaction, and biosynthesis pathway.

ChemInform Abstract: A New Route to Pyranocoumarins and Their Benzannulated Derivatives.

A new protocol based on sequential applications of three atom-economic processes viz. Claisen rearrangement, olefin isomerisation, and ring-closing diene metathesis has been developed to access a range of linear and angularly fused pyranocoumarin derivatives. Incorporation of enyne (in place of diene) metathesis and Diels–Alder reaction in the sequence has allowed the corresponding benzannulated derivatives to be prepared in good yields.

A New Route to Pyranocoumarins and Their Benzannulated Derivatives

A new protocol based on sequential applications of three atom-economic processes viz. Claisen rearrangement, olefin isomerisation, and ring-closing diene metathesis has been developed to access a range of linear and angularly fused pyranocoumarin derivatives. Incorporation of enyne (in place of diene) metathesis and Diels–Alder reaction in the sequence has allowed the corresponding benzannulated derivatives to be prepared in good yields.

Synthesis of Dihydro-1-benzazepines

A variety of dihydro-1-benzazepines (X) is prepared via a Claisen rearrangement of allyl phenyl ether (III) and a ring-closing metathesis of dienes (IX) as key steps.

New library of aminosulfonyl-tagged Hoveyda–Grubbs type complexes: Synthesis, kinetic studies and activity in olefin metathesis transformations

Seven novel Hoveyda–Grubbs precatalysts bearing an aminosulfonyl function are reported. Kinetic studies indicate an activity enhancement compared to Hoveyda’s precatalyst. A selection of these catalysts was investigated with various substrates in ring-closing metathesis of dienes or enynes and cross metathesis. The results demonstrate that these catalysts show a good tolerance to various chemical functions.

DFT Mechanistic Study on Diene Metathesis Catalyzed by Ru‐Based Grubbs–Hoveyda‐Type Carbenes: The Key Role of π‐Electron Density Delocalization in the Hoveyda Ligand

The catalytic activity and catalyst recovery of two heterogenized ruthenium-based precatalysts (H and NO(2)(4)) in diene ring-closing metathesis have been studied by means of density functional calculations at the B3LYP level of theory. For comparison and rationalization of the key factors that lead to higher activities and higher catalyst recoveries, four other Grubbs-Hoveyda complexes have also been investigated. The full catalytic cycle (catalyst formation, propagation, and precatalyst regeneration) has been considered. DFT calculations suggest that either for the homogeneous and heterogenized systems the activity of the catalysts mainly depends on the ability of the precursor to generate the propagating carbene. This ability does not correlate with the traditionally identified key factor, the Ru...O interaction strength. In contrast, precatalysts with lower alkoxy-dissociation energy barriers and lower stabilities compared with the propagating carbene also present larger C1-C2 bond length (i.e., lower pi character of the C-C bond that exists between the metal-carbene (Ru=C) and the phenyl ring of the Hoveyda ligand). Catalyst recovery, regardless of whether a release-return mechanism occurs or not, is also mainly determined by the pi delocalization. Therefore, future Grubbs-Hoveyda-type catalyst development should be based on fine-tuning the pi-electron density of the phenyl moiety, with the subsequent effect on the metalloaromaticity of the ruthenafurane ring, rather than considering the modification of the Ru...O interaction.

Mechanistic insights into the ruthenium-catalysed diene ring-closing metathesis reaction

Ruthenium-catalysed ring-closing metathesis (RCM) is a powerful technique for the preparation of medium-to-large rings in organic synthesis, but the details of the intimate mechanism are obscure. The dynamic behaviour of an RCM-relevant ruthenacyclobutane complex and its reactivity with ethene were studied using low-temperature NMR spectroscopy to illuminate the mechanism of this widely used reaction. These kinetic and thermodynamic experiments allowed for mapping the energy surface of the key steps in the RCM reaction as mediated by Grubbs-type catalysts for alkene metathesis. The highest barrier along the RCM path is only 65 kJ mol(-1), which shows that this catalyst has extremely high inherent activity. Furthermore, this transition state corresponds to that connecting the intermediates in this reaction leading to ring opening of the cyclopentene product. This shows that ring closing is kinetically slightly favoured over ring opening, in addition to being driven by the loss of ethene.

Olefinic ester and diene ring-closing metathesis using a reduced titanium alkylidene.

This manuscript describes the use of a reduced titanium ethylidene reagent in olefinic ester cyclization reactions and diene RCM reactions.

Ring‐Closing Metathesis of Heteroatom‐Substituted Dienes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis of (±)-1-Phenyl-2-azabicyclo[2.2.1]heptane Derivatives - Novel NK1Receptor Ligands

The synthesis of the l-phenyl-2-azabicyclo[2.2.1]heptane derivative 2, a potential NK 1 receptor ligand, is reported. Ring-closing metathesis of diene 10 and regio- and stereoselective opening of the oxirane ring in 14 are key steps in the synthetic sequence.

Ring-Closing Metathesis of Heteroatom-Substituted Dienes

The ring-closing metathesis (RCM) of dienes that contain at least one participating heteroatom-substituted olefin is reviewed (olefins substituted with O, N, S, P, Si, B, and halogen atoms will be considered). Efforts have been made to include as many relevant examples of RCM of heteroatom-substituted dienes as possible, but due to the increasing volume of research in this area, an exhaustive coverage is not intended. Attention has focussed on diene RCM reactions catalysed by ruthenium and molybdenum alkylidene complexes, although a brief discussion of some ring-closing reactions of titanium alkylidene species is provided. Other metathesis reactions such as enyne RCM, cross-metathesis and ROMP are not included.

Highly Efficient Ru−Pseudohalide Catalysts for Olefin Metathesis

Ruthenium alkylidene complexes containing one aryloxide "pseudohalide" ligand catalyze ring-closing metathesis of diene and ene-yne substrates with exceptionally high efficiency. Chromatographic removal of Ru residues is unexpectedly facile, offering a convenient means of isolating pure organic products in high yields.

Synthesis of Cyclic Hydrazines by Ring‐Closing Metathesis of Dienes and Enynes Tethered by an N—N Bond.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ring‐Closing Metathesis in the Synthesis of Cyclic α‐Amino Acids

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of cyclic hydrazines by ring-closing metathesis of dienes and enynes tethered by an N–N bond

Ring-closing metathesis of dienes and enynes tethered by an N–N bond produced 6- to 10-membered cyclic 1,2-diaza compounds. The enyne RCM adducts were further transformed by Diels–Alder reaction into aromatic compounds.

Highly active catalysts in alkene metathesis: first observed transformation of allenylidene into indenylidene via alkenylcarbyne--ruthenium species.

A cat. for all seasons: The transformation of the allenylidene-ruthenium complexes [RuCl(η6-arene)(CCCR2)(PR)][CF3SO3] into indenylidene species [RuCl(η6-arene)(indenylidene)(PR)][CF3SO3]2 by the simple protonation with CF3SO3H and formation of an alkenylcarbyne intermediate (see picture; arene=p-cymene) is observed by low temperature NMR experiments. The new in situ generated 18 electron ionic indenylidene species are highly active in the polymerization of cyclooctene and cyclopentene, ring-closing metathesis of dienes and enynes, and the acyclic diene metathesis of decadiene, thus making it a catalyst for all seasons.