Asymmetric Activation

Mikami, Kōichi; Terada, Masahiro; Korenaga, Takashi; Matsumoto, Y.; Ueki, Makoto; Angelaud, Rémy

doi:10.1002/1521-3773(20001016)39:20<3532::aid-anie3532>3.0.co;2-l

Cited by 157 publications

(73 citation statements)

References 314 publications

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“…Its steric hindrance is not solely responsible for moderate rates, as shown by the results with a ring fused sulfide B, with much less hindrance around the sulfur atom and epoxidation reactions which are still slow. In 3 cases, the sulfides could be recovered (entries 3,4,6). Diastereoselectivities 12 range from 73:27 to 86:14.…”

Section: Discussionmentioning

confidence: 99%

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Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Minière¹,

Reboul

Metzner³

2005

Arkivoc

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New ferrocenyl sulfides, exhibiting planar chirality, have been prepared. They incorporate various heteroatom groups, and in some cases central chirality (sulfur or carbon). They were evaluated as catalysts for the asymmetric epoxidation of aldehydes via sulfonium ylides. A onepot reaction has been achieved, involving addition of benzaldehyde, benzyl bromide, 20% molar equivalent of the ferrocenyl sulfide, sodium iodide in a mixture of tert-butanol and water. Good yields of stilbene oxide were obtained, with enantiomeric excesses up to 53%.

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Section: Discussionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7] Organocatalysis 8,9 brings specific challenges in terms of kinetic rates and efficiency. We are interested in the synthesis of oxiranes by the Johnson-Corey reaction of sulfur ylides with aldehydes.…”

Section: Introductionmentioning

confidence: 99%

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Minière¹,

Reboul

Metzner³

2005

Arkivoc

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“…20 The lability of such complexes can be traced down to titanium(IV) oxophylicity, itself responsible of the tendency of titanium complexes to form homo or hetero aggregates, as well as of titanium reactivity towards oxygen donors such as water or alcohols, 21,22 not underscoring the capacity of titanium complexes to undergo inter or intramolecular rearrangements. 23 Accordingly, among the additional operational variables which need to be controlled at the optimization step of a titanium(IV)-catalyzed procedure, stoichiometry is a major factor to be adjusted, 24,25 as well as the presence of poisons or activators, 26,27 either chiral, 28 or achiral. 29 Moreover, other apparently trivial matters such as the order of addition of reactants, 30 the aging of the precatalytic mixture, 31 as well as other procedural issues such as the presence or absence of molecular sieves, 32 or even their drying procedure, 33 quite often affect the efficiency of titanium(IV)-catalyzed enantioselective chemistry.…”

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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“…Binaphthol has been widely used in organic synthesis as a chiral auxiliary and in its deprotonated form, it offers a nucleophilic center, (i.e., oxyanion) in a highly asymmetric environment [46]. Here, the chirality comes from a hindered axis of rotation between the naphthyl groups rather than a stereogenic atom.…”

Section: Resultsmentioning

confidence: 99%

Stereoselectivity in the collision-activated reactions of gas phase salt complexes

Gronert

Fagin

Okamoto

2004

J. Am. Soc. Mass Spectrom.

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The collision-activated dissociations (CAD) of gas phase salt complexes composed of chiral ions were studied in a quadrupole ion trap mass spectrometer. Because both partners in the salt are chiral, diastereomeric complexes can be formed (e.g., RR, RS). Two general types of complexes were investigated. In the first, the complex was composed of deprotonated binaphthol and a chiral bis-tetraalkylammonium dication. CAD of these complexes leads to the transfer of a proton or an alkyl cation to the binaphtholate leading to a singly-charged tetraalkylammonium cation. During CAD, diastereomeric complexes give significantly different product distributions indicating reasonable stereoselectivity in the process. In the second system, the complexes involved a peptide dianion and a chiral tetraalkylammonium cation. These systems may be viewed as very simple models for the interactions of peptides/proteins with small chiral molecules. Again, stereoselectivity was evident during CAD, but the extent was dependent on the nature of the peptide and not observable in some cases. To better understand the structural features needed to achieve stereoselectivity in gas phase salt complexes, representative transition states were modeled computationally. The results suggest that it is critical for the asymmetry of the nucleophile (i.e., anion) to be well represented in the vicinity of its reactive center. T he high sensitivity and rapid analysis capabilities of mass spectrometry make it an attractive methodology for solving a wide range of analytical problems. However, stereochemical issues are a challenge because a mass-to-charge ratio provides no direct information with regards to the stereochemistry of a species. Nonetheless, many workers have developed novel approaches for gaining stereochemical information from mass spectrometric data [1,2]. Much of this work has focused on the development of methods that could be used to determine the enantiomeric purity of a product mixture . Like many condensed phase approaches to enantiomeric analysis, the methods rely on complexing the analyte with a substrate of known chirality. This leads to the formation of a pair of diastereomers (assuming that the analyte is not enantiomerically pure). The diastereomers are not equivalent and as a result have different stabilities, kinetic reactivities, and dissociation patterns. These differences can be exploited (i.e., by comparison to data for known standards) and used to determine the enantiomeric purity of a sample. Cooks [3][4][5][6][7][8][9][10][11][12][13][14][15][16], Dearden , , Speranza [27][28][29][30][31][32][33][34][35], and others have provided useful examples of this approach to stereochemical analysis.Along with methods for analyzing the enantiomeric purity of products, there is a growing need for the development of new reaction processes that are stereoselective. In general, these processes have been probed in the condensed phase, but there is no reason why mass spectrometry could not also be used to screen gas phase reactions for stereo...

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Asymmetric Activation

Cited by 157 publications

References 314 publications

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

Synthesis of planar chiral ferrocenyl sulfides and evaluation as catalysts for the asymmetric epoxidation of aldehydes

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

Stereoselectivity in the collision-activated reactions of gas phase salt complexes

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