ELECTROANALYSIS, Issue 17 2006
Raluca-Ioana Stefan-van, Staden
Abstract Four enantioselective, potentiometric membrane electrodes (EPMEs) based on carbon paste impregnated with ,-, ,-, 2-hydroxyl-3-trimethylammoniopropyl-,-(as chloride salt) and ,-cyclodextrins, were proposed as a chiral selectors for assay of S-flurbiprofen raw materials and in its pharmaceutical formulation Froben 100 tablets. The best response was obtained when ,-cyclodextrin was used for the electrode design. The four EPMEs showed very low detection limits (of 10,8 to 10,9 mol/L magnitude orders). The surfaces of the electrodes are easily renewable by simply polishing on an alumina paper. [source]

Electro-Organocatalysis: Enantioselective ,-Alkylation of Aldehydes

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 23 2010
Xuan-Huong Ho
Abstract The asymmetric organocatalyzed ,-alkylation of aldehydes via a cationic radical enamine intermediate was performed under environmentally benign electro-oxidation conditions without the use of chemical oxidants. To promote the desired ,-alkylation reaction of aldehydes, various aldehydes with xanthene or cycloheptatriene groups were exposed to electro-organocatalytic conditions to afford optically active ,-substituted aldehydes (,-alkylated aldehydes) in good yield. A reaction mechanism involving the cationic radical enamine was proposed based on the cyclic voltammetry (CV) results, DFT calculations, and control experiments. [source]

A Highly Enantioselective and Catalytic Aryl Transfer Reaction Using Mixed Triarylbismuthane and Dialkylzinc Reagents

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2007
Itaru Sato
Abstract Highly enantioselective and catalytic aryl transfer reactions to aromatic aldehydes by using mixed triarylbismuthane and dimethylzinc reagents were studied. In the presence of a chiral ,-amino alcohol catalyst, chiral diarylmethanols with up to 97,% ee were obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Mannich and O -Alkylation Reactions of Tetraalkoxyresorcin[4]arenes , The Use of Some Products in Ligand-Assisted Reactions

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 22 2006
Benjamin R. Buckley
Abstract The measurement of the pKa of racemic tetramethoxyresorcin[4]arenes explains the failure to obtain good yields in attempted Mannich reactions of these substrates under classical reaction conditions. The failure is related to the lack of adequate concentrations of the iminium ions that results from the reduced acid strength of tetraalkoxyresorcin[4]arenes compared with that of the parent octahydroxyresorcin[4]arenes. However, the preparation of a series of Mannich bases derived from racemic tetraalkoxyresorcin[4]arenes was accomplished under microwave-assisted aprotic reaction conditions and the use of preformed iminium ion intermediates. When the reactions were carried out with the use of chiral bis(aminol) ethers, mixtures of diastereomers were obtained that could be separated by flash chromatography. The absolute configurations of the enantiomerically pure tetrabenzoxazine derivatives were established in some cases by X-ray crystallographic analysis and by a comparison of the nuclear magnetic resonance spectroscopic data. The alkylation of racemic tetramethoxyresorcin[4]arenes was achieved with the use of an excess of 2-bromo- N -[(R)-(+)-(,-methylbenzyl)]acetamide in acetonitrile containing potassium carbonate. Enantioselective ligand-assisted reactions of aromatic aldehydes are also reported with the use of dialkylzinc reagents both in the absence and in the presence of terminal alkynes.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Organocatalyzed Highly Enantioselective and anti -Selective Construction of ,-Butenolides through Vinylogous Mukaiyama Aldol Reaction

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 8 2010
Ning Zhu
Abstract The formation of chiral ,-butenolides has been achieved with good yields (up to 90%), high enantioselectivity (up to 91%) and diastereoselectivity (up to 9/1, anti -selective) through an organocatalyzed vinylogous Mukaiyama aldol reaction of 2-(trimethylsilyloxy)furan and aldehydes. A wide range of chiral ,-butenolides was obtained under mild conditions by this methodology. [source]

Copper-Catalyzed Enantioselective [2+2],Cycloadditions of 2-Nitrosopyridine with Ketenes

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 6 2010
Indranil Chatterjee
Abstract Copper(I)-catalyzed [2+2],cycloadditions of various ketenes with 2-nitrosopyridine to afford synthetically highly valuable 1,2-oxazetidine-3-ones are shown to occur with good enantioselectivities. The thermal uncatalyzed process furnishes the unstable regioisomeric oxazetidinone. Density function theory (DFT) calculations give evidence that the reaction occurs via a concerted [2+2],cycloaddtion pathway. [source]

Silver Acetate/TF-BiphamPhos-Catalyzed endo -Selective Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylides with Vinyl Phenyl Sulfone

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2009
Gang 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]

The Direct, Enantioselective, One-Pot, Three-Component, Cross-Mannich Reaction of Aldehydes: The Reason for the Higher Reactivity of Aldimine versus Aldehyde in Proline-Mediated Mannich and Aldol Reactions

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-13 2005
Yujiro Hayashi
Abstract In the proline-mediated Mannich and aldol reactions of propanal as a nucleophile, the aldimine prepared from benzaldehyde and p -anisidine is about 7 times more reactive than the corresponding aldehyde, benzaldehyde, as an electrophile. This higher reactivity of aldimine over aldehyde is attributed to the carboxylic acid of proline protonating the basic nitrogen atom of the aldimine more effectively than the oxygen atom of the aldehyde, an explanation which has been both experimentally and theoretically verified. [source]

Tuning Electronic and Steric Effects: Highly Enantioselective [4+1] Pyrroline Annulation of Sulfur Ylides with ,,,-Unsaturated Imines,

ANGEWANDTE CHEMIE, Issue 26 2010
Liang-Qiu Lu
Sterische und elektronische Effekte: Mithilfe einer neuartigen [4+1]-Cycloaddition von atropisomeren Schwefel-Yliden 1 und ungesättigten Iminen 2 gelingt die Synthese enantiomerenangereicherter Pyrroline 3 in hohen Ausbeuten. Die beobachteten hohen Stereoselektivitäten wurden anhand einer Konformationsanalyse der Ylide erklärt. [source]

Chiral Calcium Catalysts with Neutral Coordinative Ligands: Enantioselective 1,4-Addition Reactions of 1,3-Dicarbonyl Compounds to Nitroalkenes,

ANGEWANDTE CHEMIE, Issue 48 2009
Tetsu Tsubogo
Salz der Erde: Die ersten chiralen Erdalkalimetallkomplex-Katalysatoren wurden entwickelt. Diese Katalysatoren erwiesen sich bei asymmetrischen Additionen von ,-Dicarbonylverbindungen an Nitroalkene als sehr effektiv: Ausbeuten und Enantioselektivitäten sind hoch (bis 96 %,ee). [source]

Enantioselective, Thiourea-Catalyzed Intermolecular Addition of Indoles to Cyclic N -Acyl Iminium Ions,

ANGEWANDTE CHEMIE, Issue 34 2009
Emily
Freiwild für Indole sind N -Acyliminium-Ionen als Reaktionszwischenstufen, die unter der katalytischen Wirkung einer chiralen Thioharnstoff-Schiff-Base einer intermolekularen Addition dieser Nucleophile unterliegen. Die Methode wurde genutzt, um aus einfachen Vorstufen eine Vielfalt von funktionalisierten Indolgerüsten mit hoher Enantioselektivität aufzubauen (siehe Schema; TMS=Trimethylsilyl; R=H, Me, Vinyl, OMe, F, Cl, Br; R1=Benzyl, Methyl; n=1,2). [source]

Rhodium-Catalyzed Enantioselective and Diastereoselective Hydrogenation of ,-Ketoenamides: Efficient Access to anti 1,3-Amino Alcohols,

ANGEWANDTE CHEMIE, Issue 33 2009
Huiling Geng
Nützliche chirale Bausteine werden mit ausgezeichneter Enantio- und Diastereoselektivität bei einer Tandemhydrierung von (Z)-,-Ketoenamiden gebildet, die wiederum durch direkte Kondensation von 1,3-Diketonen mit Acetamid erhalten werden (siehe Schema). Die chiralen Aminoalkoholprodukte können durch Hydrogenolyse mit Pd/C in nützliche ,-Arylisobutylamine überführt werden. R1=Aryl, Heteroaryl, Methyl; R2=Alkyl. [source]

Enantioselective 6,,,Electrocyclizations: Pushing the Limits in Organocatalytic Pericyclic Reactions

CHEMCATCHEM, Issue 4 2010

Catalysis sans frontières: Enantioselective catalysis has been achieved for 6,, electrocyclizations. Two recent reports have shown that this particular pericyclic reaction can be carried out in a catalytic and highly enantioselective way, provided that careful design of the structure of the substrate is made. Excellent results have been obtained under organocatalytic conditions, with catalysts operating by different mechanisms. [source]

ChemInform Abstract: Enantioselective and Regiodivergent Copper-Catalyzed Conjugate Addition Trialkylaluminum Reagents to Extended Nitro-Michael Acceptors.

CHEMINFORM, Issue 41 2010
Matthieu Tissot
Abstract Regio- and enantioselective conjugate addition reaction of trimethyl aluminium (II) to nitroenynes (I) and nitrodienes (VI) is developed. [source]

ChemInform Abstract: Catalytic Enantioselective 1,3-Dipolar Cycloaddition of C,N-Cyclic Azomethine Imines with ,,,-Unsaturated Aldehydes.

CHEMINFORM, Issue 33 2010
Takuya Hashimoto
Abstract A titanium/(S)-BINOL complex catalyzes the title reaction of azomethine imines (I) to give a variety of pharmaceutically attractive chiral pyrazolo-fused tetrahydroisoquinolines. [source]

ChemInform Abstract: Chiral Spiroaminoborate Ester as a Highly Enantioselective and Efficient Catalyst for the Borane Reduction of Furyl, Thiophene, Chroman, and Thiochroman-Containing Ketones.

CHEMINFORM, Issue 23 2010
Viatcheslav Stepanenko
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]

ChemInform Abstract: Enantioselective ,-Trifluoromethylation of Aldehydes via Photoredox Organocatalysis.

CHEMINFORM, Issue 2 2010
David A. Nagib
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]

ChemInform Abstract: Enantioselective, Iridium-Catalyzed Monoallylation of Ammonia.

CHEMINFORM, Issue 2 2010
Mark J. Pouy
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]

ChemInform Abstract: Enantioselective, Thiourea-Catalyzed Intermolecular Addition of Indoles to Cyclic N-Acyl Iminium Ions.

CHEMINFORM, Issue 1 2010
Emily A. Peterson
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]

ChemInform Abstract: Rhodium-Catalyzed Enantioselective and Diastereoselective Hydrogenation of ,-Ketoenamides: Efficient Access to anti 1,3-Amino Alcohols

CHEMINFORM, Issue 51 2009
Huiling Geng
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: Palladium-Catalyzed Enantioselective ,-Arylation and ,-Vinylation of Oxindoles Facilitated by an Axially Chiral P-Stereogenic Ligand.

CHEMINFORM, Issue 50 2009
Alexander M. Taylor
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: Titanium Binolate Catalyzed Aminolysis of meso Aziridines: A Highly Enantioselective and Direct Access to 1,2-Diamines.

CHEMINFORM, Issue 42 2009
Saravanan Peruncheralathan
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: Highly Enantioselective 1,3-Dipolar Cycloaddition of Azomethine Ylides Catalyzed by AgOAc/TF-BiphamPhos.

CHEMINFORM, Issue 41 2009
Chun-Jiang Wang
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: Highly Enantioselective 1,4-Addition of Diethyl Phosphite to Enones Using a Dinuclear Zn Catalyst.

CHEMINFORM, Issue 28 2009
Depeng Zhao
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: Weak Broensted Acid,Thiourea Co-Catalysis: Enantioselective, Catalytic Protio-Pictet,Spengler Reactions

CHEMINFORM, Issue 26 2009
Rebekka S. Klausen
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: Broensted Acid Catalyzed, Enantioselective, Vinylogous Mannich Reaction of Vinylketene Silyl N,O-Acetals.

CHEMINFORM, Issue 6 2009
David S. Giera
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: Enantioselective [1,2]-Stevens Rearrangement of Quaternary Ammonium Salts.

CHEMINFORM, Issue 25 2008
A Mechanistic Evaluation.
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: Highly Regio-, Diastereo-, and Enantioselective [2 + 2 + 2] Cycloaddition of 1,6-Enynes with Electron-Deficient Ketones Catalyzed by a Cationic Rh(I)/H8 -binap Complex.

CHEMINFORM, Issue 24 2008
Ken Tanaka
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: Enantioselective, NHC-Catalyzed Bicyclo-,-lactam Formation via Direct Annulations of Enals and Unsaturated N-Sulfonyl Ketimines.

CHEMINFORM, Issue 22 2008
Ming He
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: Cationic Palladium(II)-Catalyzed Highly Enantioselective [3 + 2] Annulation of 2-Acylarylboronic Acids with Substituted Alkynes.

CHEMINFORM, Issue 17 2008
Miao Yang
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]