Home About us Contact
|
Home About us Contact | ||
|
|
||
RCM Reactions (rcm + reaction)
Selected AbstractsChemInform Abstract: Synthesis of Enantiomerically Pure Cycloalkenols via Combination Strategy of Enzyme-Catalyzed Reaction and RCM Reaction.CHEMINFORM, Issue 14 2008Han Shi-Hui Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: A Novel Synthesis of Substituted Naphthalenes via Claisen Rearrangement and RCM Reaction.CHEMINFORM, Issue 3 2002Keng-Shiang Huang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Facile Synthesis of Versatile Functionalized Amino Caprolactams Using RCM Reactions of ,-Amino Acrylamide.CHEMINFORM, Issue 34 2006Gang Liu Abstract ChemInform 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. [source] Ring-Closing Olefin Metathesis on Ruthenium Carbene Complexes: Model DFT Study of StereochemistryCHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2005Sergei F. Vyboishchikov Dr. Abstract Ring-closing metathesis (RCM) is the key step in a recently reported synthesis of salicylihalamide and related model compounds. Experimentally, the stereochemistry of the resulting cycloolefin (cis/trans) depends strongly on the substituents that are present in the diene substrate. To gain insight into the factors that govern the observed stereochemistry, density functional theory (DFT) calculations have been carried out for a simplified dichloro(2-propylidene)(imidazole-2-ylidene)ruthenium catalyst I, as well as for the real catalyst II with two mesityl substituents on the imidazole ring. Four model substrates are considered, which are closely related to the systems studied experimentally, and in each case, two pathways A and B are possible since the RCM reaction can be initiated by coordination of either of the two diene double bonds to the metal center. The first metathesis yields a carbene intermediate, which can then undergo a second metathesis by ring closure, metallacycle formation, and metallacycle cleavage to give the final cycloolefin complex. According to the DFT calculations, the stereochemistry is always determined in the second metathesis reaction, but the rate-determining step may be different for different catalysts, substrates, and pathways. The ancillary N-heterocyclic carbene ligand lies in the Ru-Cl-Cl plane in the simplified catalyst I, but is perpendicular to it in the real catalyst II, and this affects the relative energies of the relevant intermediates and transition states. Likewise, the introduction of methyl substituents in the diene substrates influences these relative energies appreciably. Good agreement with the experimentally observed stereochemistry is only found when using the real catalyst II and the largest model substrates in the DFT calculations. [source] New Indenylidene-Schiff Base-Ruthenium Complexes for Cross-Metathesis and Ring-Closing MetathesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 16 2009Abstract We here report on the stability and catalytic activity of new indenylidene-Schiff base-ruthenium complexes 3a,f through representative cross-metathesis (CM) and ring-closing metathesis (RCM) reactions. Excellent activity of the new complexes was found for the two selected RCM reactions; prominent conversion was obtained compared to the commercial Hoveyda,Grubbs catalyst 2. Moreover, excellent results were obtained for a standard CM reaction. Higher conversions were achieved with one of the indenylidene catalysts compared with Hoveyda,Grubbs catalyst. Unexpectedly, an isomerization reaction was observed during the CM reaction of allylbenzene. To the best of our knowledge, isomerization reactions in this model CM reaction in closed systems have never been described using first generation catalysts, including the Hoveyda,Grubbs catalyst. The first model CM reactions as well as the RCM reactions have been monitored using 1H,NMR. The course of the CM reaction of 3-phenylprop-1-ene (8) and cis -1,4-diacetoxybut-2-ene (9) was monitored by GC. The isomerization reaction was studied by means of GC-mass spectrometry and in situ IR spectroscopy. All catalysts were structurally characterized by means of 1H, 13C, and 31P,NMR spectroscopy. [source] Stability of Second Generation Grubbs' Alkylidenes to Primary Amines: Formation of Novel Ruthenium-Amine ComplexesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Gerald Abstract The stability of second generation Grubbs' alkylidenes to primary amines relative to the first generation derivatives is investigated. For both Grubbs' alkylidene derivatives, the tricyclohexylphosphine (PCy3) ligand is displaced by n -butylamine and diethylenetriamine. However, while displacement of PCy3 in first generation Grubbs' alkylidene derivatives results in decomposition of the catalyst, the N-heterocyclic carbene (NHC) ligand in second generation derivatives is not displaced by primary amines present in up to 100 equivalents. The result is the formation of new stable ruthenium-amine complexes. These complexes are characterized and their catalytic activity is evaluated in ring-closing metathesis (RCM) and ring-opening metathesis (ROMP) reactions. While the amine complexes evaluated were minimally active in RCM reactions, the ruthenium-butylamine complex was significantly active in ROMP and exhibited an initiation rate constant that was at least an order of magnitude greater than that of the second generation Grubbs' alkylidene from which it was synthesized. [source] [(NHC)(NHCewg)RuCl2(CHPh)] Complexes with Modified NHCewg Ligands for Efficient Ring-Closing Metathesis Leading to Tetrasubstituted Olefins,CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2010Volodymyr Sashuk Abstract Imidazolium salts (NHCewg,HCl) with electronically variable substituents in the 4,5-position (H,H or Cl,Cl or H,NO2 or CN,CN) and sterically variable substituents in the 1,3-position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)ewg] complexes. The reactions of [(NHC)RuCl2(CHPh)(py)2] with the [AgI(NHCewg)] complexes provide the respective [(NHC)(NHCewg)RuCl2(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring-closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2,0.5,mol,% at 80,°C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHCewg group with 1,3-Me,iPr and 4,5-Cl,Cl substituents and can be synthesized in 95,% isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL-NHC)(NHCewg)RuCl2(CHPh)] and [(FL-NHCewg)(NHC)RuCl2(CHPh)], with a dansyl fluorophore (FL)-tagged electron-rich NHC ligand (FL-NHC) and an electron-deficient NHC ligand (FL-NHCewg) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore-tagged ligand. In this manner, it was shown for ring-opening metathesis ploymerization (ROMP) reactions at room temperature that the NHCewg ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium. [source] | ||||||||||