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Showing 1 to 20 of 152 for “"enantioselectivity"”.
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The Triplex Diels-Alder Reaction: An Investigation of Enantioselectivity and Scope
… cyclic dienes yielded endo (4+2) adducts with enantioselectivity up to 23%. Our report is the first observation of an enantioselective photochemical cycloaddition reaction which is catalyzed by a chiral sensitizer. The mechanistic investigation suggests the presence of diastereomeric …
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Controlling the Regio- and Enantioselectivity of Iridium-Catalysed Arene Borylation Using Sulfonated Bipyridine Ligands
… interactions to control both the regio- and enantioselectivity of iridium-catalysed arene borylation, an incredibly synthetically useful transformation that commonly suffers from a lack of regioselectivity, and for which enantioselective variants are very few. The strategy followed involved …
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Iridium Catalysed Borylation as a Platform for Exploring the Use of Non-Covalent Interactions to Control Regio- and Enantioselectivity
… catalysis to address issues of regio- and enantioselectivity. In sharp contrast however their utilisation in directing the same aspects of selectivity in transition metal catalysed transformations is rather underexplored. This doctoral thesis aims to explore the use of non-covalent …
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Investigations of Catalysts Which Utilise Non-Covalent Interactions to Control Enantioselectivity in Rhodium-Catalysed Amination of C(sp3)–H Bonds
… proved effective, however, and both yield and enantioselectivity here surpassed those for the analogous alcohol-directed methodology. Variation of the amide directing group, arene-based functionality, and methylene chain length were all viable and well tolerated, with collaborative work from …
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Engineering a highly enantioselective horseradish peroxidase by directed evolution
… for synthetic chemistry. However, their enantioselectivity toward most synthetically useful, non-natural substrates is typically low. Therefore, improving enzymatic enantioselectivity toward a given substrate is a practically important but arduous task. Here we report a highly efficient …
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Development and Application of Computational Methods for the Prediction of Chiral Phosphoric Acid Catalyst Performance
… frequently revealed how these catalysts impart enantioselectivity. Thus, the vast majority of time required for reaction development is expended on the optimisation of the catalyst features. The research described here explores the ability of relating computational derived catalyst parameters to …
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Scope of enantioselective reduction of imines with trichlorosilane
… yields of the reduced product (68-85 %), the enantioselectivity depended on steric bulk in proximity to the nitrogen, steric bulk improved the enantioselectivity (up to 78 % ee), probably due to thwarting the coordination of the nitrogen to HSiCl3. 2. Aromatic heterocycles containing sulfur – …
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Chemistry with chiral lithium amides: enantiotopic group and face-selective reactions
… (up to 98% de) and the moderate to high enantioselectivity (up to 75% ee) induced by those chiral lithium amides. On the other hand, high diastereoselectivity (up to 100% de) and the low enantioselectivity were obtained from the aldol reaction of tropinone enolate with benzaldehyde …
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Synthesis and utilization of guanidine catalysts for applications directed towards the preparation of butenolide and modified amino acid derivatives
… ) amino )-3 -phenylpropan-l-ol, demonstrated enantioselectivity for a variety of adducts. Highest enantiomeric excess (ee) was afforded between dibromofuranone and p-chlorobenzaldehyde, affording the syn conformation in 96% ee and the anti in 54% ee, with an overall yield of30%. Attempts to …
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The Development of Asymmetric Palladium-Catalysed Transformations Using Chiral Sulfonated Phosphine Ligands
… at utilising non-covalent interactions to induce enantioselectivity in palladium-catalysed reactions using sulfonated phosphine ligands. Firstly, a library of achiral sulfonated phosphine ligands that are ion-paired with a chiral cation were synthesised. These ligands only had modest success in a …
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Studies of tartaric acid modified nickel supported catalysts for enantioselective hydrogenation reactions
… ca. 20 nm, proved not to have a major effect on enantioselectivity. However, the nature of the cations constituting the catalyst support was found to influence the enantioselectivity observed. Specifically, when iron or chromium were constituents of the supporting oxide matrix, …
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Transition-metal catalysis of cyclocarbonylation and cycloisomerization reactions
… and the concentration of the catalyst on the enantioselectivity of this cyclization was explored. It has been found that enynes with an octyl-, benzyl-, or allyl-amino group, positioned [beta] to the alkyne and the olefin, were cyclized with a high degree of enantioselectivity. Substrates with …
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The Application of Catalysis based on Hydrogen Bonding and Ion-pairing Interactions to Asymmetric Minisci-type Alkylations of Azines and Iridium-Catalysed C-H Borylation.
… can be applied to regioselectivity and enantioselectivity challenges in synthetic chemistry. The most widely used interactions, hydrogen bonding and ion-pairing, are employed in this thesis for the accomplishment of two important transformations in an enantioselective manner. The …
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Design and modification of rhodium and iridium N-heterocyclic carbene complexes for asymmetric transfer hydrogenation and antimicrobial activity
… alkyl ketones, and optimization studies found enantioselectivity in this system was highly sensitive to the reaction temperature, NHC ligand, and amino acid. Incorporation of secondary amino acids was essential to enantioselectivity. Aryl ketones were reduced in high conversion and …
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Development and Mechanistic Investigation of Indium(III)-Catalysed Hydrosilane Reduction of Imines
… of computational methods in understanding how enantioselectivity is induced in specific reactions is a powerful time-saving tool for organic chemists. By investigating the reaction pathway, specifically the enantiodetermining transition state, factors that result in an increased energy …
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Design, synthesis, and evaluation of conformationally rigid naproxen chiral selectors
… chromatographically and demonstrate enhanced enantioselectivity towards naproxen and other members of profens, an important group of non-steroidal anti-inflammatory drugs(NSAIDs). The improved enantioselectivity is believed to stem from a highly preorganized disposition of the key functional …
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The Synthesis and Application of a Chiral Sulfonated Phosphine Ligand to Asymmetric Transition-Metal Catalysis
… allowing sSPhos to influence site- and enantioselectivity when employed as a ligand for transition-metal catalysis. The development of a linear chemical resolution route, using (R)-BINOL as a chiral auxiliary, is described. This route allows access to sSPhos in its enantiopure form. The …
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Control of selectivity in palladium-catalysed cross-coupling reactions using a sulfonated phosphine ligand
… interactions to influence site-selectivity and enantioselectivity during palladium-catalysed cross-coupling reactions – a category of transformations used widely by synthetic chemists for many purposes. This thesis focuses on members of the privileged dialkylbiarylphosphine ligand class, …
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Parameters influencing yeast-mediated reactions in an organic solvent
… of yeast (2g/mmole substrate) and with good enantioselectivity (97% ee). Although some esters required larger amounts of yeast in order to attain complete conversion to the product, the isolated yields were generally higher than 70% and the enantioselectivity was normally greater than 97% ee. …
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The Design and Application of Ion-paired Ligands to Address Selectivity Challenges in Transition Metal Catalysed Oxygen and Nitrogen Transfer Reactions
… cinchona alkaloids and have been shown to induce enantioselectivity in challenging reaction types: iridium- catalysed C-H borylation, and rhodium-catalysed C-H amination and alkene aziridination. Chapter 2 explores the synthesis of novel ion-paired metalloporphyrins. Porphyrins are a privileged …
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