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Showing 1 to 20 of 77 for “"enantiomeric excess"”.
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Progress towards a highly efficient and accurate platform for enantiomeric excess determination
Enantiomeric excess (ee) determination remains as the bottleneck for high throughput screening of asymmetric catalysts. The work described herein sought to expand on two previously developed ee sensing assays from our lab– an iron based amine assembly and a zinc based multicomponent assembly. To …
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Vanadium-katalysierte, asymmetrische Epoxidierung von Allylalkoholen
… acids were shown to led to an increase in the enantiomeric excess of the products obtained. The readily available tert-butyl hydroperoxide was found to be the oxidant of choice. Environmentally friendly and halide free toluene was used as the solvent. Applying the optimised reaction conditions …
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Photoresolvable compounds: Towards a chiroptical-liquid crystalline switch
… optical properties that determine the degree of enantiomeric excess that one can attain at the photostationary state, the g value. Two strategies to increase the g value were investigated: exciton coupling and energy transfer. Energy transfer was shown to be an efficient strategy in the design of …
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Asymmetric Syntheses With (-)-Sparteine-Complexed Benzylic and Allylic Organolithium Reagents
… >20 were obtained, as calculated using the enantiomeric excess of the conjugate addition product.
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Chirale Phosphortriamide und Phosphin-Phosphoramidite als Liganden für die asymmetrische Katalyse
… with different transition metals. The highest enantiomeric excess obtained was 48% for Ni-catalysed hydrovinylation of styrene. The phosphine-phosphoramidites were especially tested as ligands for asymmetric hydrogenation employing Rhodium or Iridium as the catalytically active metal. In the …
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Studies of alpha-lithioamine synthetic equivalents: I. Elaboration of primary amines. II. Detection of an intermediate in the lithiation of a benzylic urea
… the corresponding products with up to 57% enantiomeric excess. Lithiation of N-tert-butyl-N-benzyl carbamates resulted in rearrangement to phenylglycine derivatives. These related investigations are also discussed.
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Derivatisierungsreaktionen von Cinchona-Alkaloiden und eine Cinchona-Alkaloid-katalysierte asymmetrische Synthese von 2,5-Diarylphopholanen
… 2-phospholenes in quantitative yields with an enantiomeric excess of up to 91%. The 2,5-diphenyl-2-phospholeneamide was hydrolyzed to the phospholenic acid in aqueous acid. Diastereoselective reduction of the unsaturated acid with sodium in liquid ammonia and ammonia sulphate as proton source …
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Studies on Resolution of Enantiomeric Dialkylaryl Sulfonium Ions with NMR Shift Reagents
… shift reagent, is focused on for assessment of enantiomeric excess and resolution of methyl sulfonium ions. A series of alkylmethylphenylsulfonium ions were analyzed, where alkyl is ethyl (I), butyl(H), octyl (III), and benzyl(IY). The praseodymium agent gives base-lined resolution of the ortho …
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Explorations with optically active, cage-annulated crown ethers.
… that are capable of differentiating between enantiomeric "guest" molecules during host-guest complexation have been prepared via incorporation of chiral elements into the crown ring skeleton. The ability of these crown ethers to recognize the enantiomers of guest salts, i.e., (+) a-methyl …
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The Tandem Inter [4+2]/[3+2] Cycloadditions of Nitroalkenes: The Bridged-Mode
… that were reduced using nickel boride to provide enantiomerically enriched aminocyclopentanes in good yields and high enantiomeric excess. Additionally, the Lewis acid employed in the $\lbrack 4 + 2\rbrack$ cycloaddition was found to impart a remarkable influence on the stereochemical outcome of …
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CoMFA Study of Chiral Catalysts
… 70% of the variance in the observed enantiomeric excess can be attributed to the steric field and the remainder of the variance to the electrostatic field. Suggestions about how to improve the performance of inefficient catalysts are given the thesis.
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Total synthesis of (S)-4-hydroxy-[a]-Lapachone
… 42613 was used to yield the target compound. The enantiomeric excess of the product was determined to be ~98% by using 1H NMR chiral shift analysis. The overall yield is 80/0. The biological activity of (S)-4-hydroxy-alapachone and its acetate are under investigation.
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Enantioselective nickel catalysis : exploiting activated C-H bonds
… product with the best enantioselectivity (enantiomeric excess ca. 70%), however in low yield.
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The asymmetric synthesis of amino acids via electrophilic glycinates
… furnishes the zwitterionic α-amino acids in high enantiomeric excess. Dissolving metal reduction of 134 permits the preparation of unsaturated amino acids while use of erythro-4-t-butoxycarbonyl-5,6-diphenyl-2,3,5,6-tetrahydro-1,4-oxazin-2-one 160 allows the direct preparation of t-BOC protected …
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Hydrierung im invertierten Zweiphasensystem scCO 2/H 2 O
… used. Hydrogenation of itaconic acid led to an enantiomeric excess of 97-98% ee (S) at full conversion and with recycling of the catalyst. Hydrogenation of Methyl-2-acetamidoacrylate gave full conversion and an enantiomeric excess of >98% ee (R) for at least five cycles. Another subject was the …
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Development and Mechanistic Investigation of Indium(III)-Catalysed Hydrosilane Reduction of Imines
… importance inter alia for the development of enantiomerically pure drugs. The application 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 …
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Development of an Intelligent Heart-Cut Liquid Chromatography System for Chiral Analysis of Chemical Processes
… dimension uses a chiral column to measure the enantiomeric excess (ee) of the chiral analyte and the effluent from the third dimension is re-analyzed via a fourth dimension to determine if any loss of chirality has occurred resulting from the analytical method itself. Performance of the setup …
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Asymmetrische Cycloisomerisierung von 1,6-Dienen
… diethylester in 91% regioselectivity and 79% enantiomeric excess. Furthermore the use of halide free precursors of the type [Ni(allyl)(cod)][Y] with weakly coordinating counterions Y led to a strong increase in activity without loss in regio- and only with small loss in enantioselectivity. …
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Chiral expression at the nanoscale origin and recognition of chirality
… dichroism spectroscopy and NSOM. The small enantiomeric excess achieved in experiments was explained by the limits of chirality determination methods. It was found that crystals formed in enantiomeric excess were of opposite chirality to the SAM they were grown on. This confirms previous …
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Zur asymmetrischen Synthese von C-Azanucleosiden und 2-Amino-1,3-diolen
… were synthesized in high diastereomeric and enantiomeric excess however the titled compound could not be obtained. In the second part a diastereo- and enantioselective synthesis of various 2-amino-1,3-diols (de>=96%, ee = 90-94%) is presented. Starting from the Dioxanon-SAMP-Hydrazone, the …
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