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Chiral Induction (chiral + induction)

Distribution by Scientific Domains

Chemistry	90%

Distribution within Chemistry

Organic Chemistry	55%
General & Introductory Chemistry	22%

Selected Abstracts

Complete Chiral Induction from Enantiopure 1,2-Diamines to Benzophenone-Based Achiral Bisphosphane Ligands in Noyori-Type RuII Catalysts

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 16 2006
Qing Jing
Abstract We report the design and synthesis of a novel class of RuII catalysts (3) composed of achiral benzophenone-based bisphosphane ligands and enantiopure 1,2-diamines for the asymmetric hydrogenation of aryl ketones. The developed catalysts show excellent enantioselectivities (up to 97,% ee) and activities (up to S/C = 10,000) in the hydrogenation of a variety of aromatic ketones.Complete chiral induction from the enantiopure 1,2-diamine to the achiral bisphosphane ligand was observed. The coordination of the C=O moiety in 3 to the cationic RuII center is considered to be of key importance in providing a higher thermodynamic and kinetic rotation barrier for the flexible bisphosphane ligand, resulting in the preferential formation of only one diastereomer, and thus explaining the high enantioselectivity of the catalyst. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

ChemInform Abstract: Exploration of Chiral Induction on Epoxides in Lipase-Catalyzed Epoxidation of Alkenes Using (2R,3S,4R,5S)-(-)-2,3:4,6-Di-O-isopropylidiene-2-keto-L-gulonic Acid Monohydrate.

CHEMINFORM, Issue 46 2009
Kuladip Sarma
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]

Chiral Induction, Memory, and Amplification in Porphyrin Homoaggregates Based on Electrostatic Interactions

CHEMPHYSCHEM, Issue 6 2009
LiXi Zeng Dr.
Abstract Supramolecular chirality in two configurational homoaggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D - and L -alanine in acidic water (see picture). The chirality can be further memorized and enforced through strong electrostatic interactions between TPPS aggregates and achiral poly(allylamine) [PAA]. Supramolecular chirality in two configurational homoaggregates of anionic meso -tetrakis(4-sulfonatophenyl)porphyrin (TPPS) can be induced by D - and L -alanine (Ala) in acidic water, respectively. The induced supramolecular chirality can be further memorized and enforced, even after complete removal of Ala or in the presence of excess Ala with the opposite configuration, through strong electrostatic interactions with achiral poly(allylamine) [PAA]. The ionic chiral interactions between TPPS and Ala or PAA are characterized by means of UV/Vis absorption and circular dichroism spectrometry. Fluorescence spectroscopy and atomic force microscopy are used as complementary techniques. On the basis of the comprehensive experimental results, a possible mechanism for chiral induction, memory, and amplification of TPPS homoaggregates by chiral amino acids and achiral PAA is proposed. Thus, we demonstrate a novel strategy to realize chiral memory in supramolecular systems by polyelectrolytes through hierarchical electrostatic self-assembly. [source]

Complete Chiral Induction from Enantiopure 1,2-Diamines to Benzophenone-Based Achiral Bisphosphane Ligands in Noyori-Type RuII Catalysts

Asymmetric Lithiation of Boron Trifluoride-Activated Aminoferrocenes: An Experimental and Computational Investigation

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010
Costa Metallinos
Abstract Tertiary aminoferrocenes complexed to boron trifluoride (BF3) are shown to undergo asymmetric lithiation with alkyllithiums in the presence of bulky chiral 1,2-diaminocyclohexane ligands. This reaction represents the first BF3 -activated asymmetric lithiation of a prochiral aromatic amine and the first such transformation to be mediated by a chiral diamine other than (,)-sparteine. The process provides rapid access to a broad range of enantiomerically enriched 2-substituted-1-aminoferrocenes, including derivatives with uncommon substitution patterns that are of interest in catalysis. The enantioselectivity of the process is high enough (87:13 to 91:9 er) to allow for isolation of single enantiomers of several products after simple recrystallization as either the free aminoferrocenes or their ammonium fluoroborate salts. Both antipodes of the planar chiral 2-substituted-1-aminoferrocene products are accessible, as confirmed by single crystal X-ray diffraction analysis of two compounds with opposite relative stereochemistry. Single-point calculation of thirty-two different transition states of the reaction at the M06-2X/6-311+g(2d,2p) level produced a computational model that correctly predicted both the sense and extent of chiral induction. Three factors appeared to play important roles in determining enantioinduction during lithiation of BF3 -complexed tertiary aminoferrocenes: (i) the maintenance of a highly organized eight-membered ring transition state; (ii) the existence of a strong Li,,,F contact which placed the chiral diamine ligand in close proximity to the ferrocene substrate; (iii) the orientation of the sterically demanding N -alkyl groups of the chiral diamine additives, either away or towards, the aminoferrocene and the alkyllithium. The model may serve as a predictive tool for the rational design of new ligands for this and related asymmetric lithiations. [source]

Asymmetric Strecker Reaction of Ketoimines Catalyzed by a Novel Chiral Bifunctional N,N, -Dioxide

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 18 2006
Xiao Huang
Abstract A novel bifunctional N,N, -dioxide derived from L -prolinamide was employed to catalyze the enantioselective Strecker reaction of a range of N -tosyl ketoimines, and an effective additive was used to improve the reactivity (up to 99,% yield) as well as the enantioselectivity (up to 91,% ee). In addition, a rational transition state was proposed to elucidate the origin of chiral induction in which an S -adduct was produced. [source]

Long-range effects of chirality in aromatic poly(isocyanide)s

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 10 2006
David B. Amabilino
Abstract The preparation of optically active atropoisomeric polymers which present chiral backbones, thanks to induction during their synthesis from stereogenic centers, located far away from the skeleton is possible, thanks principally to semirigid conformations of the promesogenic spacers between them. The result is that chiral "information" can be passed as far as 21 Å from the asymmetric center to the carbon atom that forms the polymeric chain in poly(isocyanide)s. The sense of chiral induction in these conformationally rigid polymers parallels the helical sense of the cholesteric phases, as well as to the helical senses of chiral smectic C phases, induced by the monomers in nematic and smectic C phases, respectively. All these phenomena obey the odd,even rules proposed for chiral sense changes in these liquid crystalline phases. Noncovalent interactions play an important part in the induction process, in which steric arguments can be used to justify the inductions observed. The methodology can be used to prepare macromolecules, which display switching behavior upon thermal or electrochemical stimulus. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3161,3174, 2006 [source]

Mechanistic Investigation of Chiral Phosphoric Acid Catalyzed Asymmetric Baeyer,Villiger Reaction of 3-Substituted Cyclobutanones with H2O2 as the Oxidant

CHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2010
Senmiao Xu Dr.
Abstract The mechanism of the chiral phosphoric acid catalyzed Baeyer,Villiger (B,V) reaction of cyclobutanones with hydrogen peroxide was investigated by using a combination of experimental and theoretical methods. Of the two pathways that have been proposed for the present reaction, the pathway involving a peroxyphosphate intermediate is not viable. The reaction progress kinetic analysis indicates that the reaction is partially inhibited by the ,-lactone product. Initial rate measurements suggest that the reaction follows Michaelis,Menten-type kinetics consistent with a bifunctional mechanism in which the catalyst is actively involved in both carbonyl addition and the subsequent rearrangement steps through hydrogen-bonding interactions with the reactants or the intermediate. High-level quantum chemical calculations strongly support a two-step concerted mechanism in which the phosphoric acid activates the reactants or the intermediate in a synergistic manner through partial proton transfer. The catalyst simultaneously acts as a general acid, by increasing the electrophilicity of the carbonyl carbon, increases the nucleophilicity of hydrogen peroxide as a Lewis base in the addition step, and facilitates the dissociation of the OH group from the Criegee intermediate in the rearrangement step. The overall reaction is highly exothermic, and the rearrangement of the Criegee intermediate is the rate-determining step. The observed reactivity of this catalytic B,V reaction also results, in part, from the ring strain in cyclobutanones. The sense of chiral induction is rationalized by the analysis of the relative energies of the competing diastereomeric transition states, in which the steric repulsion between the 3-substituent of the cyclobutanone and the 3- and 3,-substituents of the catalyst, as well as the entropy and solvent effects, are found to be critically important. [source]

Chiral Induction, Memory, and Amplification in Porphyrin Homoaggregates Based on Electrostatic Interactions

Asymmetric Synthesis of the C(17),C(28) Subunit of Didemnaketal B

CHINESE JOURNAL OF CHEMISTRY, Issue 9 2007
Xue-Qiang Li
Abstract The stereocontrolled synthesis of the C(17),C(28) fragment 3 of didemnaketal B was accomplished in 21 steps from the natural (R)-(+)-pulegone and (S)-(,)-citronellal. The key steps involved diastereoselective construction of two chiral carbon centers through the intramolecular chiral induction and uncommon Julia olefination of ketone forming the E -trisubstituted C(22),C(23) double bound. [source]