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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
provided by the
Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 11 to 17 of 17 (0.047 seconds)| 11 |
Synthesis of bis(2,2,2-trifluoroethyl) β-ketophosphonates from bis(2,2,2-trifluoroethyl) 1-alkynylphosphonates via enamine vinyl phosphonatesDePizzo, Ashley 20 October 2010 (has links)
No description available.
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Towards the development of direct methodology to enantioenriched α-alkylated aldehydesCharlton, Andrew January 2013 (has links)
Enantiopure α-alkyl-substituted aldehydes are widely recognised as important building blocks in synthesis. Despite this, methods to prepare such substrates are limited. Strategically, asymmetric intermolecular S<sub>N</sub>2 α-alkylation represents a highly straightforward transformation, but still remains an elusive feat. This thesis describes efforts to address this challenge, with attempted access to enantioenriched α-alkyl aldehydes by way of C-alkylation of chiral, non-racemic, hindered aldenamines using simple alkyl halides. Enamines derived from four types of auxiliary (a tropane, an oxazolidine, a pyrrolidine and a homotropane) have been prepared, and their alkylation profile examined. While the desired levels of asymmetric induction were not attained, use of the tropane and homotropane auxiliaries, which differ only by a single methylene group, interestingly, gave complimentary diastereocontrol during alkylation with EtI. The observed stereoselectivity is supported by density functional studies performed for ethylation of both enamines. Additionally, in the course of preparing the homotropane a highly efficient asymmetric synthesis of a homotropinone bearing gem-α-substitution has been developed.
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Perfluroaryl azides : Reactivities, Unique Reactions and their Applications in the Synthesis of Theranostic AgentsXie, Sheng January 2015 (has links)
The work centersaround perfluoroaryl azides (PFAAs), and theirability to undergo certain fast and robusttransformations. The chemistry was furtherappliedfor biomedical applications. The first section focuses on the azide-aldehyde-amine cycloaddition using PFAAs. Experimental and computational investigations uncovered a fast azide-enamine cycloaddition to form triazolines, which spontaneously rearrange into stable amidine products. In addition, this transformation was explored in the formulation of pure nanodrugs. Because this reaction can introduce a phenyl and a perfluoroaryl moiety enabling supramolecular interactions near the antibiotic drug, the resulting ciprofloxacin derivatives formed nano-sized aggregates by precipitation, which displayed aggregation-induced emission for bacterial imaging as well as enhanced size-dependent antibacterial efficacy. In the second section, the high electrophilicity of PFAAs was explored to transform azides to aryl amides. The reactivity of PFAAs in the thioacid/azide reaction was studied. In addition, PFAAs were discovered to react with phenylacetaldehyde to form aryl amidesviaan azide-enol cycloaddition, similar tothe perfluoroaryl azide-aldehyde-amine reaction.This strategyof amide synthesiswas furthermoregeneralized through a combination of base-catalyzed azide-enolate cycloaddition reaction and acid-or heat-promoted rearrangement of triazolines. The last section describes a type of azide fluorogens whose fluorescence can be switched on by alight-initiated intramolecular nitrene insertion intoa C-H bond in the neighboring aromaticring. These fluorogenic structures were efficiently accessed via the direct nucleophilic aromatic substitution of PFAAs. / <p>QC 20150903</p>
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Dynamic Systems : Enzymatic Synthesis, Exchange Reactions and Applications in Materials ScienceZhang, Yang January 2015 (has links)
This thesis is divided into three parts, revolving around the developments of dynamic systems utilized in dynamic kinetic resolution (DKR) and constitutional dynamic chemistry (CDC). The first section gives an introduction to constitutional dynamics, the core concept of this thesis. Constitutional dynamics can be tuned through reversible interactions. Then, the basic principles of constitutional dynamics in DKR and CDC are discussed, along with their applications. The second section explores the asymmetric synthesis of oxazolidinone derivatives using lipase catalysis through kinetic resolution (KR) and dynamic kinetic resolution. In the first example, synthetic protocol to enantioenriched 5-phenyloxazolidin-2-ones is described, where a kinetically controlled carbamation is followed by lipase-catalyzed cyclization. In contrast to the 5-substituted species, the synthesis of 3-phenyloxazolidin-2-one derivatives could be achieved through lipase-catalyzed cascade O- and N- alkoxycarbonylations in one pot. Furthermore, this KR system could be coupled to a ruthenium-catalyzed racemization process of 1,2-aminoalcohols, thus providing an efficient DKR methodology for asymmetric transformations. The third section focuses on dynamic systems built through reversible covalent reactions. In the first example, a selective gelation process is described, and employed to resolve dynamic imine systems consisting of gelator candidates. In the second example, reversible reactions with aldehyde enamines are presented, including enamine formation and exchange reactions. In particular, Bi(III) and Sc(III) were discovered to accelerate the enamine exchange reactions by 50-400 times, in which the equilibria could be reached within hours. The last example describes reversible nitroaldol reactions in aqueous media, where rapid and efficient equilibration was identified for selected structures in neutral phosphate buffer. / <p>QC 20150911</p>
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Ein Baukastensystem zum universellen Aufbau kleiner rigidifizierter Peptidomimetika und spirocyclopropanierter Wirkstoffanaloga / A toolbox-system for the formation of small rigid peptidomimetics and spirocyclopropanated drug-analoguesLimbach, Michael 02 November 2004 (has links)
No description available.
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β-Aminosubstituted α,β-Unsaturated Fischer Carbene Complexes as Precursors for Complex Oligocyclic Molecules - Basics and Applications / β-Amino-substituierte α,β-Ungesättigte Fischer Carben-Komplexeals Vorläufer für Kompexe Oligocyclische Moleküle - Grundforschung und AnwendungenWu, Yao-Ting 03 July 2003 (has links)
No description available.
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Untersuchungen zur Synthese von Yohimban- und Campthoteca-Alkaloiden durch Domino-Knoevenagel-Hetero-Diels-Alder-Reaktion / Efforts toward the total synthesis of yohimban and campthoteca alkaloids via domino Knoevenagel-hetero-Diels-Alder reactionKlapa, Katharina Anna 17 January 2007 (has links)
No description available.
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