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Substrate Scope (substrate + scope)
Selected AbstractsTantalum,Amidate Complexes for the Hydroaminoalkylation of Secondary Amines: Enhanced Substrate Scope and Enantioselective Chiral Amine Synthesis,ANGEWANDTE CHEMIE, Issue 44 2009Patrick Eisenberger Dr. Mono- und Diamidat-Tantalkomplexe wurden synthetisiert und in der katalytischen ,-Alkylierung sekundärer Amine getestet (siehe Schema). Eine spontane ,-Wasserstoffabstraktion führt zu einem katalytisch aktiven Tantalaaziridin, das als erste Verbindung seiner Klasse vollständig charakterisiert werden konnte. [source] ChemInform Abstract: Exploring the Substrate Scope of the Ru(II)-Catalyzed Kharasch Reaction.CHEMINFORM, Issue 1 2008Eskender Mume 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] Diverse Asymmetric Quinolizidine Synthesis: A Stereodivergent One-Pot ApproachADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 2-3 2010Wei Zhang Abstract A diverse stereodivergent organocatalytic one-pot addition/cyclization/annulation sequence to optically active quinolizidine derivatives from easily available starting materials is presented. The one-pot sequence relies on a pyrrolidine-catalyzed enantioselective conjugate addition of electron-deficient amide ,-carbons to ,,,-unsaturated aldehydes, spontaneous hemiaminal formation and acid-catalyzed/mediated N -acyliminium ion cyclization to give the quinolizidine framework. Simple tuning of the reaction conditions in the N -acyliminuim ion cyclization step provides a diastereomeric switch, which gives access to both of the two bridgehead epimers through kinetic, thermodynamic or chelation control. The methodology display a broad substrate scope that is demonstrated by the stereoselective formation of indolo-, thieno-, benzofuro-, furo- and different benzoquinolizidine derivatives with high atom efficiency, up to >99% ee and up to >95:5 dr. Due to its efficiency, synthetic diversity and operational simplicity, this protocol has the potential to find important use as a key step in natural product synthesis, biochemistry and pharmaceutical science. The stereochemical outcome of the one-pot sequence was investigated, and the mechanism and origin of stereoselectivity of the different steps is discussed. [source] Silver Acetate/TF-BiphamPhos-Catalyzed endo -Selective Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylides with Vinyl Phenyl SulfoneADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Gang Liang Abstract The first catalytic endo -selective 1,3-dipolar cycloaddition of azomethine ylides and vinyl phenyl sulfone has been developed successfully. The highly efficient silver acetate (AgOAc)/TF-BiphamPhos catalytic system exhibited high reactivity, excellent diastereoselectivity (>98:2), good enantioselectivity (67,92% ee) and broad substrate scope under mild conditions. [source] Trapping of Active Methylene Intermediates with Alkenes, Indoles or Thiols: Towards Highly Selective Multicomponent ReactionsADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Yanlong Gu Abstract In this paper, a basic method to access new multicomponent reactions (MCRs) is reported. The mechanism of these MCRs is based on the trapping of methylene intermediates, formed in situ by reaction of formaldehyde with electron-rich carbons, with alkene, thiol or indole derivatives. According to our strategy, a wide range of valuable skeletons has been obtained in a one-pot reaction, thus allowing a minimization of waste, cost and labor. The presented methodology exhibits a broad substrate scope and electron-rich carbons in the ,-position of a hydroxy or carbonyl group were found to be particularly efficient. More generally, this work offers new tools for creating molecular complexity and diversity from one of the simplest organic building blocks, formaldehyde. [source] Directed Evolution of an Enantioselective Enoate-Reductase: Testing the Utility of Iterative Saturation MutagenesisADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009Despina Abstract Directed evolution utilizing iterative saturation mutagenesis (ISM) has been applied to the old yellow enzyme homologue YqjM in the quest to broaden its substrate scope, while controlling the enantioselectivity in the bioreduction of a set of substituted cyclopentenone and cyclohexenone derivatives. Guided by the known crystal structure of YqjM, 20 residues were selected as sites for saturation mutagenesis, a pooling strategy based on the method of Phizicky [M. R. Martzen, S. M. McCraith, S. L. Spinelli, F. M. Torres, S. Fields, E. J. Grayhack, E. M. Phizicky, Science1999, 286, 1153,1155] being used in the GC screening process. The genes of some of the hits were subsequently employed as templates for randomization experiments at the other putative hot spots. Both (R)- and (S)-selective variants were evolved using 3-methylcyclohexenone as the model substrate in the asymmetric bioreduction of the olefinic functionality, only small mutant libraries and thus minimal screening effort being necessary. Some of the best mutants also proved to be excellent catalysts when testing other prochiral substrates without resorting to additional mutagenesis/screening experiments. Thus, the results constitute an important step forward in generalizing the utility of ISM as an efficient method in laboratory evolution of enzymes as catalysts in organic chemistry. [source] Significant Self-Acceleration Effects of Nitrile Additives in the Rhodium-Catalyzed Conversion of Aldoximes to Amides: A New Mechanistic AspectADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2009Min Kim Abstract It was found that the catalytic activity of rhodium complexes was highly sensitive to the type of N-heterocyclic carbene (NHC) ligands in the conversion of aldoximes to amides. Among those species examined, the (cyclooctadiene)rhodium chloride-carbene complex Rh(cod)(IMes)Cl exhibited the highest reactivity when it was employed in combination with a Brønsted acid, thus allowing mild reaction conditions. A significant rate acceleration effect resulting from the addition of nitrile additives was also observed. With the new protocol, the substrate scope of aldoximes has been widely expanded to include sterically congested and electronically varied derivatives. On the basis of detailed mechanistic studies, it is proposed that the reaction proceeds mainly via intramolecular electrophilic addition of aldoxime to rhodium-bound nitrile, which is different from the generally postulated two-step route: dehydration of aldoxime to nitrile followed by hydration of the latter intermediate. [source] Iron-Catalyzed Ligand-Free Carbon-Selenium (or Tellurium) Coupling of Arylboronic Acids with Diselenides and DitelluridesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2009Min Wang Abstract Carbon-selenium and carbon-tellurium cross-couplings of arylboronic acids with diselenides and ditellurides have been catalyzed by iron(0), iron(II) chloride or iron(III) chloride without any ligand and additive in the air. The method yields the corresponding unsymmetrical diorgano monoselenides and monotellurides in good to excellent yields, displays a broad substrate scope, and is simple, convenient, effective, economical and environmentally friendly. [source] Simple and Fast Synthesis of New Axially Chiral Bipyridine N,N, -Dioxides for Highly Enantioselective Allylation of AldehydesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Aneta Kadl, íková Abstract Unsymmetrically 3,3,-substituted axially chiral bis(tetrahydroisoquinoline) N,N,- dioxides can be prepared in just three steps. They exhibit unique catalytic activity (turnover frequency, enantioselectivity, substrate scope) in the asymmetric allylation of aromatic aldehydes (up to 96% ee). The product of the enantioselective allylation of benzaldehyde served as a building block for the preparation of an intermediate useful in the enantioselective synthesis of diospongines. [source] Increasing the Scope of Palladium-Catalyzed Cyanations of Aryl ChloridesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 4 2009Thomas Schareina Abstract An improved protocol for the palladium-catalyzed cyanation of electron-rich aryl chlorides with potassium ferrocyanide {K4[Fe(CN)6]} is presented. Compared to previous procedures the substrate scope is significantly broadened. [source] Bismuth- and Hafnium-Catalyzed Hydroamination of Vinyl Arenes with Sulfonamides, Carbamates, and CarboxamidesCHEMISTRY - AN ASIAN JOURNAL, Issue 1 2007Hongbo Qin Abstract Catalytic intermolecular hydroamination of vinyl arenes is described. Our initial investigation revealed that a Bi(OTf)3/[Cu(CH3CN)4]PF6 system previously developed for catalytic intermolecular hydroamination of 1,3-dienes was suitable for hydroamination of a styrene with sulfonamides, but the substrate generality of this system was unsatisfactory. Several metals were screened to expand the substrate scope, and a new Hf(OTf)4/[Cu(CH3CN)4]PF6 system was determined to be highly suitable. The combination of Hf(OTf)4 and [Cu(CH3CN)4]PF6 efficiently promoted the hydroamination of various vinyl arenes, including less-reactive vinyl arenes with electron-withdrawing groups. This strategy was applied to sulfonamides, carbamates, and carboxamides, and products were obtained in up to 99,% yield with 0.3,10,mol,% catalyst loading. [source] | ||||||||||||||||||||||