Insight into the Mechanism of the Asymmetric Addition of Alkyl Groups to Aldehydes Catalyzed by Titanium−BINOLate Species

Balsells, Jaume; Davis, Timothy J.; Carroll, Patrick J.; Walsh, Patrick J.

doi:10.1021/ja0171658

Cited by 190 publications

(188 citation statements)

References 103 publications

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“…In addition, the metal center is hardest. [13] Use of this catalyst resulted in the formation of nearly all 4 following completion of the reaction. However, when the ratio of the two catalyst compounds was increased, the Lewis acidity of the catalyst decreased and a small amount of compound 3 was formed.…”

Section: Resultsmentioning

confidence: 99%

Asymmetric Addition of Phenylacetylene to Aldehydes Catalyzed by β‐Sulfonamide Alcohol‐Titanium Complex

Lin

et al. 2006

Adv Synth Catal

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A series of b-sulfonamide alcohol ligands were synthesized from l-phenylalanine. Titanium complexes of these compounds were used to catalyze the asymmetric addition of phenylacetylene to a number of aldehydes. When the conditions were optimized, 20 mol % of ligand 8a catalyzed the reaction with high enantioselectivity (up to 98% ee) and good yield (up to 92%). When a small amount of MeOH was added to the reaction as a modifier, as little as 5 mol % of ligand was required to efficiently catalyze the reaction under very mild conditions, resulting in an ee of up to 99% and good yield.

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Section: Resultsmentioning

confidence: 99%

Asymmetric Addition of Phenylacetylene to Aldehydes Catalyzed by β‐Sulfonamide Alcohol‐Titanium Complex

Lin

et al. 2006

Adv Synth Catal

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“…39 For the particular case of the BINOLateTicatalyzed enantioselective addition of dialkylzinc organometallics to aldehydes, Walsh and co-workers have concluded that the actual catalyst should be the dinuclear mixed dimer (BINOLate)Ti(OiPr) 2 .Ti(OiPr) 4 D MD , in accordance with the absence of NLE in the catalytic reaction. 40 A quite different picture was drawn, however, from the closely related BINOLateTi allylation of ketones, thereby suggesting that seemingly minor issues might have a profound influence on the actual mechanism (in this case, the presence of isopropanol gives rise to a large improvement of ee). 41 In another important study, the solution structure of the major species formed by mixing Binol and Ti(OiPr) 4 (no removal of iPrOH in this case), in different ratios (from 1:1 to 1:8), was examined by means of extensive NMR, DOSY and CD studies by Salvadori and co-workers.…”

Section: Introductionmentioning

confidence: 99%

Curtin–Hammett versus non-Curtin–Hammett frameworks in optimizing the enantioselective binolam/titanium(IV)-catalyzed cyanobenzoylation of aldehydes: Part 2

Saá

Baeza

Nájera

et al. 2011

Tetrahedron: Asymmetry

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Graphical AbstractTo create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered. Leave this area blank for abstract info. Stereochemistry AbstractTo create your abstract, type over the instructions in the template box below. Fonts or abstract dimensions should not be changed or altered. You may insert more abstracts by copying this box or by using the menu option to insert a stereochemistry abstract.Authors' names here --- * Corresponding author for additional computational details (J.M.S.) Tel.: +34-971173262; fax: +34-971173426; e-mail: jmsaa@uib.es IntroductionEvidences have been provided in support of the involvement of an LABB (Lewis Acid-Brønsted Base) cooperative, 1 dual action mechanism for "Binolam-AlCl"-catalyzed enantioselective cyanation reactions, the overall reaction taking place through an indirect route involving hydrocyanation followed by Ofunctionalization. In these reactions, according to the reported data, the aluminium atom of the in situ-generated catalyst plays the role of a Lewis acid (LA), while the N atom acts as a Brønsted base (BB) in catching the available HCN in the mixture (either present in the commercial samples, or being generated by induced hydrolysis of the cyanide reagent employed induced by trace amounts of water contained in the molecular sieves, or otherwise).2,3,4,5 Unfortunately, such a detailed knowledge of the mechanism of action of the analogous "Binolam-TiX 2 " catalysts is lacking, among other reasons because the structure of the titanium(IV) complexes initially formed (precatalysts), as well as that of the actual catalysts, is not well-known, 6 in spite of recent advances in the field. 7 In this work we will try to show that our "Binolam-TiX 2 " catalyzed cyanobenzoylations are particularly difficult to optimize because these reactions do not fit within the usual Curtin-Hammett (C-H) construction. 8 More on the contrary, as it will be shown below, "Binolam-TiX 2 " catalyzed cyanobenzoylations rather behave as a non-Curtin-Hammett framework. So, let us shed light upon the C-H principle prior to analyze and discuss the results.The basic Curtin-Hammett (C-H)/Winstein-Holness (W-H) kinetic system illustrated in Scheme 1 describes the relationship between two equilibrating molecules (or two conformations of a single molecule) and their reactivity.9 For our present purposes we can think of A and B as equilibrating catalysts involved in an asymmetric catalytic system. A R T I C L E I N F O ABSTRACT Article history: Received Received in revised form Accepted Available onlineExtensive experimental and computational studies have been carried out upon the enantioselective titanium(IV)-catalyzed cyanobenzoylation of aldehydes using 1:n Binolam:Ti(OiPr) 4 mixtures as precatalysts, with the purpose of identifying the key mechanistic aspects governing enantioselectivity. HCN and isopropyl benzoate were detected in the reacting mixtures. This, as well as the reaction response to the presence of an exog...

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“…Under dilute reaction conditions, the heterochiral dimer is soluble and enters into the catalytic cycle upon its break down into monomers, thereby resulting in the absence of an NLE. Walsh and co-workers [40] detected a weak (À)-NLE in the case of the asymmetric addition of dimethylzinc to aldehydes mediated by binolate-titanium complexes (10 mol % binol) [Eq. (6)].…”

mentioning

confidence: 99%

“…[41] Walsh and co-workers found that the NLEs disappeared under catalytic conditions. [40] The authors ruled out the involvement of oligomeric species and the possibility of binol acting as a monodentate ligand. 3 ] complex was presumed to be the active species.…”

mentioning

confidence: 99%

Nonlinear Effects in Asymmetric Catalysis

Satyanarayana¹,

Abraham²,

Kagan³

2008

Angew Chem Int Ed

500

273

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There is a need for the preparation of enantiomerically pure compounds for various applications. An efficient approach to achieve this goal is asymmetric catalysis. The chiral catalyst is usually prepared from a chiral auxiliary, which itself is derived from a natural product or by resolution of a racemic precursor. The use of non-enantiopure chiral auxiliaries in asymmetric catalysis seems unattractive to preparative chemists, since the anticipated enantiomeric excess (ee) of the reaction product should be proportional to the ee value of the chiral auxiliary (linearity). In fact, some deviation from linearity may arise. Such nonlinear effects can be rich in mechanistic information and can be synthetically useful (asymmetric amplification). This Review documents the advances made during the last decade in the use of nonlinear effects in the area of organometallic and organic catalysis.

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Insight into the Mechanism of the Asymmetric Addition of Alkyl Groups to Aldehydes Catalyzed by Titanium−BINOLate Species

Cited by 190 publications

References 103 publications

Asymmetric Addition of Phenylacetylene to Aldehydes Catalyzed by β‐Sulfonamide Alcohol‐Titanium Complex

Asymmetric Addition of Phenylacetylene to Aldehydes Catalyzed by β‐Sulfonamide Alcohol‐Titanium Complex

Curtin–Hammett versus non-Curtin–Hammett frameworks in optimizing the enantioselective binolam/titanium(IV)-catalyzed cyanobenzoylation of aldehydes: Part 2

Nonlinear Effects in Asymmetric Catalysis

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