scholarly journals Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

2011 ◽  
Vol 7 ◽  
pp. 1421-1435 ◽  
Author(s):  
Lukas Hintermann ◽  
Mauro Perseghini ◽  
Antonio Togni
Keyword(s):  
Asymmetric Catalysis ◽  
Lewis Acids ◽  
Enantiomeric Excess ◽  
Acetonitrile Solution ◽  
Reaction Intermediates ◽  
Reaction Parameters ◽  
Dichloromethane Solution ◽  
Ligand Structure ◽  
Catalyst Complex ◽  
Experimental Findings

Titanium-based Lewis acids catalyze the α-fluorination of β-ketoesters by electrophilic N–F-fluorinating reagents. Asymmetric catalysis with TADDOLato–titanium(IV) dichloride (TADDOL = α,α,α',α'-tetraaryl-(1,3-dioxolane-4,5-diyl)-dimethanol) Lewis acids produces enantiomerically enriched α-fluorinated β-ketoesters in up to 91% enantiomeric excess, with either F–TEDA (1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate)) in acetonitrile solution or NFSI (N-fluorobenzenesulfonimide) in dichloromethane solution as fluorinating reagents. The effects of various reaction parameters and of the TADDOL ligand structure on the catalytic activity and enantioselectivity were investigated. The absolute configuration of several fluorination products was assigned through correlation. Evidence for ionization of the catalyst complex by chloride dissociation, followed by generation of titanium β-ketoenolates as key reaction intermediates, was obtained. Based on the experimental findings, a general mechanistic sketch and a steric model of induction are proposed.

Theoretical Prediction of the Enantiomeric Excess in Asymmetric Catalysis. An Alignment-Independent Molecular Interaction Field Based Approach

2005 ◽  
Vol 70 (22) ◽  
pp. 9025-9027 ◽  
Author(s):  
Simone Sciabola ◽  
Alexander Alex ◽  
Paul D. Higginson ◽  
John C. Mitchell ◽  
Martin J. Snowden ◽  
...  
Keyword(s):  
Theoretical Prediction ◽  
Asymmetric Catalysis ◽  
Molecular Interaction ◽  
Enantiomeric Excess ◽  
Interaction Field ◽  
Molecular Interaction Field

An examination of VANOL, VAPOL, and VAPOL derivatives as ligands for asymmetric catalytic Diels–Alder reactions

2006 ◽  
Vol 84 (10) ◽  
pp. 1487-1503 ◽  
Author(s):  
Douglas P Heller ◽  
Daniel R Goldberg ◽  
Hongqiao Wu ◽  
William D Wulff
Keyword(s):  
Asymmetric Catalysis ◽  
Methyl Acrylate ◽  
Lewis Acids ◽  
Alder Reaction ◽  
Diels Alder ◽  
Asymmetric Catalytic ◽  
Diels Alder Reaction ◽  
Positive Cooperativity ◽  
Derivatives Of ◽  
Methyl Phenyl

Several derivatives of the vaulted biaryl ligand VAPOL were prepared and evaluated as chiral ligands for aluminum Lewis acids in the catalytic asymmetric Diels–Alder reactions of methyl acrylate and methacrolein with cyclopentadiene. The substituents on VAPOL were introduced into the 6- and 6′-positions in an effort to further extend the chiral pocket of the major groove, which contains the phenol functions at the 4- and 4′-positions. The set of four new ligands that have been prepared have the following groups introduced into the 6- and 6′-positions of VAPOL: bromide, methyl, phenyl and 3,5-di-t-butylphenyl. All of these ligands give lower asymmetric inductions than the unsubstituted VAPOL for the Diels–Alder reactions of both methyl acrylate and methacrolein. The positive cooperativity of added carbonyl compounds on the autoinduction in the Diels–Alder reaction of methyl acrylate and cyclopentadiene were also investigated with the VANOL and VAPOL ligands as well as the 6,6′-dibromo and 6,6′-diphenyl derivatives of VAPOL. Only the reaction with VAPOL showed any significant positive cooperativity. The reaction with VANOL was sluggish at –78 °C, but at higher temperatures, the reaction did exhibit positive cooperativity that was similar to that of VAPOL. Finally, no positive cooperativity was observed with the VAPOL ligand for the reaction of methacrolein and cyclopentadiene.Key words: Diels–Alder, asymmetric catalysis, vaulted biaryl ligands, VANOL, VAPOL.

ASYMMETRIC CATALYSIS OF ACYL TRANSFER BY LEWIS ACIDS AND NUCLEOPHILES. A REVIEW

2000 ◽  
Vol 32 (4) ◽  
pp. 331-365 ◽  
Author(s):  
Alan C. Spivey ◽  
Adrian Maddaford ◽  
Alison J. Redgrave
Keyword(s):  
Asymmetric Catalysis ◽  
Lewis Acids ◽  
Acyl Transfer

scholarly journals Rigid and concave, 2,4-cis-substituted azetidine derivatives: A platform for asymmetric catalysis

2018 ◽  
Author(s):  
Akina Yoshizawa ◽  
Antonio Feula ◽  
Louise Male ◽  
Andrew G. Leach ◽  
John Fossey
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Asymmetric Catalysis ◽  
Enantiomeric Excess ◽  
Platinum Complex ◽  
Crystal Structure Analysis ◽  
Single Crystal Structure ◽  
Complex Catalyst ◽  
Reaction Conditions ◽  
Absolute Stereochemistry

A series of single enantiomer, 2,4-<i>cis</i>-disubstituted amino azetidines were synthesised and used as ligands for copper-catalysed Henry reactions of aldehydes with nitromethane. Optimisation of ligand substituents and the reaction conditions was conducted. The enantiomeric excess of the formed products was highest when alkyl aldehydes were employed in the reaction (>99% e.e.). The absolute stereochemistry of one representative azetidine derivative salt was determined by analysis of the Flack parameter of an XRD single crystal structure. The origin of selectivity in catalysis was investigated computationally, revealing the importance of the amino-substituent in determining the stereochemical outcome. A racemic platinum complex of a <i>cis</i>-disubstituted azetidine is examined by XRD single crystal structure analysis with reference to its steric parameters, and analogies to the computationally determined copper complex catalyst are drawn.<br>

scholarly journals Enantiodivergent Non-Linear Effects in Asymmetric Catalysis

2020 ◽  
Author(s):  
Yannick Geiger ◽  
thierry achard ◽  
aline maisse-françois ◽  
Stephane Bellemin-Laponnaz
Keyword(s):  
Metal Complexes ◽  
Asymmetric Catalysis ◽  
Catalytic System ◽  
Catalyst Concentration ◽  
Enantiomeric Excess ◽  
Product Formation ◽  
Experimental Results ◽  
Non Linear ◽  
Linear Effects ◽  
Special Case

In this paper, we theoretically discuss the enantiodivergent product formation in asymmetric catalysis, a process in which the sign of the overall product enantiomer switches upon a change of catalyst concentration. The presented model is based on a catalytic system that consists of both discrete and dimeric aggregated metal complexes, in competition and in equilibrium. These concepts were then expanded to a non-enantiopure catalyst, giving rise to enantiodivergent non-linear effects – a special case of a hyperpositive non-linear effects where the product enantiomer’s sign switches upon a change of the catalyst enantiomeric excess. Different cases are considered allowing a discussion of the influence of the parameters governing both models. Finally, we present experimental results that support the enantiodivergence while varying the concentration of enantiopure catalyst or while varying the enantiomeric excess of the catalyst, using chiral N-methylephedrine as a ligand for the enantioselective addition of dimethylzinc to benzaldehyde.

scholarly journals A unified machine-learning protocol for asymmetric catalysis as a proof of concept demonstration using asymmetric hydrogenation

2020 ◽  
Vol 117 (3) ◽  
pp. 1339-1345 ◽  
Author(s):  
Sukriti Singh ◽  
Monika Pareek ◽  
Avtar Changotra ◽  
Sayan Banerjee ◽  
Bangaru Bhaskararao ◽  
...  
Keyword(s):  
Machine Learning ◽  
Asymmetric Catalysis ◽  
Predictive Power ◽  
Enantiomeric Excess ◽  
Asymmetric Hydrogenation ◽  
Gradient Boosting ◽  
Steady Increase ◽  
Asymmetric Transformations ◽  
Asymmetric Catalysts ◽  
Extreme Gradient Boosting

Design of asymmetric catalysts generally involves time- and resource-intensive heuristic endeavors. In view of the steady increase in interest toward efficient catalytic asymmetric reactions and the rapid growth in the field of machine learning (ML) in recent years, we envisaged dovetailing these two important domains. We selected a set of quantum chemically derived molecular descriptors from five different asymmetric binaphthyl-derived catalyst families with the propensity to impact the enantioselectivity of asymmetric hydrogenation of alkenes and imines. The predictive power of the random forest (RF) built using the molecular parameters of a set of 368 substrate–catalyst combinations is found to be impressive, with a root-mean-square error (rmse) in the predicted enantiomeric excess (%ee) of about 8.4 ± 1.8 compared to the experimentally known values. The accuracy of RF is found to be superior to other ML methods such as convolutional neural network, decision tree, and eXtreme gradient boosting as well as stepwise linear regression. The proposed method is expected to provide a leap forward in the design of catalysts for asymmetric transformations.

ChemInform Abstract: [Cr(Salen)] as a “Bridge” Between Asymmetric Catalysis, Lewis Acids and Redox Processes

ChemInform ◽  
2010 ◽  
Vol 33 (31) ◽  
pp. no-no
Author(s):  
Marco Bandini ◽  
Pier Giorgio Cozzi ◽  
Achille Umani-Ronchi
Keyword(s):  
Asymmetric Catalysis ◽  
Lewis Acids ◽  
Redox Processes

Autoxidation catalysed by transition metal complexes. I. The coordinative mechanism for phenylmethanethiol autoxidation catalysed by Bis[dimercaptomaleonitrilato(2 -)]cobaltate(2-) [Co(mnt)2]22- in acetonitrile solution

1977 ◽  
Vol 30 (2) ◽  
pp. 305 ◽  
Author(s):  
IG Dance ◽  
RC Conrad
Keyword(s):  
Electron Transfer ◽  
Oxygen Consumption ◽  
Transition Metal Complexes ◽  
Homogeneous Catalysis ◽  
Kinetic Data ◽  
Ligand Substitution ◽  
Acetonitrile Solution ◽  
Intramolecular Electron Transfer ◽  
Catalyst Complex

The homogeneous catalysis of phenylmethanethiol autoxidation ���������������������� 2PhCH2SH+O2 → PhCH2SSCH2Ph+H2O2 by [Co(mnt)2]22- (mnt, doubly deprotonated dimercaptomaleonitrile) in acetonitrile solution buffered with excess PhMe2N and PhMe2NH+ClO4- at 18.0�C is described. Effective catalysis occurs in this medium, with catalyst complex decomposition less than 1 mole % of the turnover. Spectrophotometric and oxygen-consumption kinetic data indicate that the mechanism involves initial coordination of the thiolate to [Co(mnt)2]- to form an intermediate which then, with Bronsted acid assistance, interacts with oxygen to form a second intermediate, which dissociates to products and regenerates [Co(mnt)2]22-. It is concluded that the role of the catalyst is to sequentially coordinate and activate the reactants and facilitate intramolecular electron transfer from thiolate to oxygen, without itself undergoing reduction or oxidation or dithiolene ligand substitution.

scholarly journals Enantiodivergent Non-Linear Effects in Asymmetric Catalysis

2020 ◽  
Author(s):  
Yannick Geiger ◽  
thierry achard ◽  
aline maisse-françois ◽  
Stephane Bellemin-Laponnaz
Keyword(s):  
Metal Complexes ◽  
Asymmetric Catalysis ◽  
Catalytic System ◽  
Catalyst Concentration ◽  
Enantiomeric Excess ◽  
Product Formation ◽  
Experimental Results ◽  
Non Linear ◽  
Linear Effects ◽  
Special Case

In this paper, we theoretically discuss the enantiodivergent product formation in asymmetric catalysis, a process in which the sign of the overall product enantiomer switches upon a change of catalyst concentration. The presented model is based on a catalytic system that consists of both discrete and dimeric aggregated metal complexes, in competition and in equilibrium. These concepts were then expanded to a non-enantiopure catalyst, giving rise to enantiodivergent non-linear effects – a special case of a hyperpositive non-linear effects where the product enantiomer’s sign switches upon a change of the catalyst enantiomeric excess. Different cases are considered allowing a discussion of the influence of the parameters governing both models. Finally, we present experimental results that support the enantiodivergence while varying the concentration of enantiopure catalyst or while varying the enantiomeric excess of the catalyst, using chiral N-methylephedrine as a ligand for the enantioselective addition of dimethylzinc to benzaldehyde.

scholarly journals Enantiodivergent Non-Linear Effects in Asymmetric Catalysis

2020 ◽  
Author(s):  
Yannick Geiger ◽  
thierry achard ◽  
aline maisse-françois ◽  
Stephane Bellemin-Laponnaz
Keyword(s):  
Metal Complexes ◽  
Asymmetric Catalysis ◽  
Catalytic System ◽  
Catalyst Concentration ◽  
Enantiomeric Excess ◽  
Product Formation ◽  
Experimental Results ◽  
Non Linear ◽  
Linear Effects ◽  
Special Case

In this paper, we theoretically discuss the enantiodivergent product formation in asymmetric catalysis, a process in which the sign of the overall product enantiomer switches upon a change of catalyst concentration. The presented model is based on a catalytic system that consists of both discrete and dimeric aggregated metal complexes, in competition and in equilibrium. These concepts were then expanded to a non-enantiopure catalyst, giving rise to enantiodivergent non-linear effects – a special case of a hyperpositive non-linear effects where the product enantiomer’s sign switches upon a change of the catalyst enantiomeric excess. Different cases are considered allowing a discussion of the influence of the parameters governing both models. Finally, we present experimental results that support the enantiodivergence while varying the concentration of enantiopure catalyst or while varying the enantiomeric excess of the catalyst, using chiral N-methylephedrine as a ligand for the enantioselective addition of dimethylzinc to benzaldehyde.

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