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  • About
  • 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.
31

The synthesis of homochiral polythiophenes

Golighar, Abdul Munaff January 1995 (has links)
No description available.
32

Asymmetric synthesis of β- and γ- amino acids

Zammit, Charlotte Maria January 2015 (has links)
This thesis is concerned with the development of new synthetic routes for the asymmetric syntheses of a range of β- and γ-amino acids. Chapter 1 introduces the various biological activities displayed by cyclic β-amino acid containing compounds together with their occurrence in pharmaceutical molecules and β-peptides. Some of the most commonly used synthetic strategies for the preparation of carbocyclic β-amino acids are briefly described, with the focus on the formation and functionalisation of a five-membered carbocyclic ring. Chapter 2 describes a full investigation into a highly diastereoselective Ireland-Claisen rearrangement of stereodefined allyl β-amino esters to access enantiopure α-substituted β-amino acid products. The synthetic utility of this methodology is highlighted by its application in the asymmetric syntheses of five previously inaccessible C(5)-substituted 1,2-anti-1,5-syn-transpentacins. Chapter 3 delineates investigations into a highly diastereoselective conjugate additionelimination protocol for the preparation of a cyclic β'-amino-α,β-unsaturated ester. Subsequent chemo- and diastereoselective conjugate addition reactions of Grignard reagents and lithium amides to this substrate enabled the asymmetric syntheses of four C(5)-substituted 1,2-anti-1,5-syn-transpentacins and two five-membered β,β'-diamines. Chapter 4 details the extension of the protocol developed in Chapter 3 for the conjugate addition of Grignard reagents to a range of acyclic γ-(N,N-dibenzylamino)-substituted α,β-unsaturated esters. Elaboration of the β,γ-disubstituted γ-amino ester products culminated in the asymmetric syntheses of six β,γ-disubstituted γ-amino acids. Chapter 5 chronicles the preparation of an azabicyclic α,β-unsaturated ester, following which attempts towards the asymmetric synthesis of various substituted pyrrolizidines using a conjugate addition protocol are subsequently described. Chapter 6 contains full experimental procedures and characterisation data for all compounds synthesised in Chapters 2, 3, 4 and 5.
33

A new type of chiral bipyridine: synthesis and application in asymmetric catalytic cyclopropanation.

January 1999 (has links)
by Wong Hei Lam Harry. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references (leaves 60-67). / Abstract also in Chinese. / Library's copy: Copy 2 imperfect, p. 60-63 missing. / Table of Contents --- p.i / Acknowledgments --- p.iii / Abbreviations --- p.iv / Abstract --- p.v / Abstract (Chinese) --- p.vi / Chapter CHAPTER I --- GENERAL INTRODUCTION / Chapter 1.1.1 --- Different biological activities of enantiomers --- p.1 / Chapter 1.1.2 --- Approach to enantiomerically pure compounds --- p.3 / Chapter 1.1.3 --- Principle of asymmetric synthesis --- p.4 / Chapter 1.1.4 --- Asymmetric catalysis and chiral catalyst --- p.5 / Chapter 1.2.1 --- Asymmetric cyclopropanation: general introduction --- p.6 / Chapter 1.2.2 --- Asymmetric cyclopropanation: initial studies --- p.8 / Chapter 1.2.3 --- Development of c2-symmetric semicorrin and its derivatives --- p.10 / Chapter 1.2.4 --- Bisoxazolines --- p.12 / Chapter 1.2.5 --- Tridentate N donor ligands --- p.13 / Chapter 1.2.6 --- "2,2'-Bipyridines" --- p.14 / Chapter 1.2.7 --- Chiral metalloporphyrin catalyst --- p.15 / Chapter 1.2.8 --- Intramolecular asymmetric cyclopropanation --- p.16 / Chapter CHAPTER II --- DESIGN AND SYNTHESIS OF CHIRAL LIGANDS / Chapter 2.1 --- Development of atropisomeric biaryls --- p.19 / Chapter 2.2 --- "Chiral 2,2'-bipyridine ligands" --- p.19 / Chapter 2.3 --- Design of chiral ligands --- p.22 / Chapter 2.4 --- Synthesis of target ligands: synthetic strategy --- p.22 / Chapter 2.5 --- Attempted synthesis of target ligands via cross-coupling reaction --- p.22
34

The study of uloses in asymmetric expoxidation. / CUHK electronic theses & dissertations collection

January 2000 (has links)
by Leung Yiu Chung. / "2000 July." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (p. 98-102). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.
35

Asymmetric synthesis of substituted 2-aminotetralins

Aaseng, Jon Erik January 2010 (has links)
Presented in this thesis are the results obtained from the project: Asymmetric synthesis of substituted 2-aminotetralins. The initial goal was to establish new or improved routes to enantiopure 2-aminotetralin (2-AT) derivatives. The motivation for this project was based on the diverse applications various 2-ATs represent as biologically active compounds. Despite the role of 2-aminotetralins as interesting target molecules, reflected by the massive research activity in the field, no general and cost efficient route has really been established. Chapter 1 in this thesis gives an introduction to 2-ATs as biologically active compounds, as well as a brief survey of the concepts of chirality and asymmetric synthesis. Aziridines are also presented, given their role as key intermediates in our developed strategies (chapters 2-4). In chapter 2, a total synthesis of substituted (S)-2-ATs is presented, starting from natural L-aspartic acid. Two 2-AT derivatives were successfully synthesised, but especially one step (ring-closing to tetralones) proved difficult, providing up to 41% yield only. Chapter 3 is directly based on the experiences we made in the former chapter, and presents an improved route from the same starting point (chiral pool strategy utilising L-aspartic acid). Again we struggled with one specific cyclisation reaction (up to 36% yield), but the remaining steps provided overall good yields. In Chapter 4, a different approach has been targeted, i.e. asymmetric aziridination of 1,2-dihydronaphthalenes. Here, various copper, rhodium and ruthenium catalytic systems were tested with alternative nitrogen sources. While we were able to achieve quite good results for non-substituted 1,2-dihydronaphthalene, substituted substrates provided only mediocre yields and enantioselectivity. Aziridines were selectively ring-opened by catalytic hydrogenation to their respective N-protected 2-ATs in good yields.
36

New chiral bis(oxazoline) ligands for asymmetric catalysis

Le, Cong-Dung Thi 28 August 2008 (has links)
Not available / text
37

Molecular recognition of carbohydrates by a designed receptor and a formal synthesis of (+)-pancratistatin

Doyle, Timothy John 12 1900 (has links)
No description available.
38

Design and evaluation of a new Lewis acid-assisted Lewis acid catalyst system and further applications of a double-allylation reagent

Sivasubramaniam, Umakanthan Unknown Date
No description available.
39

Synthesis of camphor derived ligands for applications in asymmetric catalysis.

Boyle, Grant Alexander. January 2009 (has links)
Chiral monoterpenes such as camphor have been widely used in the development of asymmetric catalysts with varying degrees of success. Pyridyl N-donor ligands derived from camphor have been extensively studied and have proven to be very successful. C3 pendant pyridyl alcohol ligands have been neglected until this study. Herein the synthesis of a series of six novel C3 pendant ligands is described. The ligands were synthesised in six steps (seven for ligand 4) using R-(+)-camphor as the starting material. Two alternative methods for the synthesis were investigated with the second method (Method B) proving to be superior. Several difficulties with regards to regioisomers and diastereomers were overcome in establishing the procedure for the synthesis of the ligands. The final compounds were successfully synthesised in moderate yields with absolute regio- and stereo-control. The ligands were evaluated as chiral catalysts in a series of different reactions. The first of these was the alkylation of a series of aldehydes using diethylzinc. This reaction was investigated in order to compare the efficacy of the novel compounds to previous camphor derived pyridyl alcohol ligands. All previous molecules of this type have been evaluated as catalysts in this reaction with varying degrees of success. The novel ligands successfully catalysed this reaction with moderate to good enantioselectivity (up to 85% ee). The results obtained showed these compounds to be significantly superior to a previous analogous C2 pendant β-amino alcohol reported in literature. The results were also comparable to other camphor derived pyridyl alcohol ligands reported previously. The synthesis of ligands 1-4 as well as their evaluation as catalysts in the alkylation of aldehydes with diethylzinc is discussed in detail in chapter 2 (Paper 1). The second reaction in which the ligands were evaluated was the Henry (Nitroaldol) reaction. This reaction has not seen many camphor derived ligands applied as catalysts. Two additional derivatives (5-6) were synthesized and all the compounds were screened as catalysts in this reaction. The ligands successfully catalyzed the reaction with good to excellent yields but only moderate selectivity (up to 56% ee). The details of this evaluation are discussed in chapter 3 (Paper 2). The final reaction in which the ligands were evaluated was the Diels-Alder reaction of 2- acrolyloxazolidinone with cyclopentadiene. The reaction was again successfully catalysed in moderate to good yields with good endo:exo selectivity but fairly poor stereoselectivity (up to 43% ee). Computational models of the proposed complexes were developed in order to explain the poor observed selectivity. The details of this study are reported in chapter 4 (Paper 3). Chapter 5 (Paper 4) involves a NMR and computational investigation of some of the ligands. Complete NMR elucidation using 2D NMR techniques were carried out for the selected ligands. Optimisation of the ligands using high level DFT calculations was carried out in order to aid in the visualisation of potential through space interactions within each molecule. / Thesis (Ph.D.)-University of KwaZulu-Natal, 2009.
40

New bisphosphine ligands for asymmetric catalysis

Carey, Joseph Vincent January 1991 (has links)
The success of homogeneous asymmetric catalysis has been attributed to the structure and stereochemistry of the coordinated ligand(s). The most effective ligands are C<sub>2</sub>-symmetrical bisphosphines containing either a rigid chiral backbone linking two PPh<sub>2</sub> units or a bisphosphine, DIPAMP containing two chiral phosphine units linked by an achiral backbone. The synthesis of P-chiral ligands of this type has been severely hindered by the lack of a general synthetic route allowing the incorporation of phosphorus chirality without the need for separation of diastereomeric precursors or resolution of intermediate enantiomers. The objective of this work was to develop a general synthetic route to homochiral bulky arylphosphines with substantial flexibility in the groups at phosphorus and extend the approach to new P-chiral bisphosphines. In one approach, diastereomerically pure (2R, 4S, 5R)-2,5-diphenyl-3,4-dimethyl-1,3,2-oxazaphospholidine was prepared directly from PhPCl<sub>2</sub> using l-ephedrine as a chiral auxiliary. Stereospecific oxidation using Bu<sup>t</sup>OOH gave the corresponding P-oxide which was shown to have R-stereochemistry at phosphorus by single-crystal X-ray diffraction studies. The compound reacted regiospecifically with ortho-anisylmagnesium bromide to afford the product formed by P-O bond cleavage with >96% d.e. and with retention of configuration at phosphorus as demonstrated by single-crystal X-ray diffraction studies. The l-ephedrine residue was replaced by O-methyl under acid-catalysis with inversion of configuration and with >95% e.e., the reaction was monitored by <sup>1</sup>H n.m.r. spectroscopy which gave t<sub>1/2</sub> of ca. 30 min. Attempts to incorporate para-fluorophenol using similar conditions led to the isolation of the pyrophosphinate in low yield. The OMe residue in the methyl (ortho-anisyl)phenylphosphinate was readily displaced by aliphatic Grignard reagents giving the corresponding phosphine oxides with inversion of configuration and with >95% e.e. Displacement of methoxy using aryl magnesium bromides showed similar enantioselectivity but in lower chemical yield, however the corresponding arylmagnesium chlorides were more efficient. In a second approach, diastereomerically pure (2R, 4S, 5R)-2-chloro-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine was prepared from PCl<sub>3</sub> and l-ephedrine. The compound underwent diastereoselective P-C1 cleavage with aryl Grignard and aryllithium reagents with net retention of configuration at phosphorus and with 90% d.e. Oxidation of the ortho-anisyl derivative afforded (2R, 4S, 5R)-2-(ortho-anisyl)-3,4-dimethyl-5-phenyl-1,3,2-oxazaphospholidine-2-oxide which was subsequently reacted with a range of bulky aryl Grignard reagents to afford the corresponding biarylphosphinamides with retention of configuration at phosphorus. Subsequent acid-catalysed methanolysis and displacement of the methoxy residue with PhMgCl afforded a range of bulky arylphosphine oxides with defined configuration at phosphorus with >95% e.e. as determined by <sup>1</sup>H n.m.r. methods. (S)-ortho-anisyl (meta-anisyl)phenylphosphine oxide underwent regiospecific ortho-lithiation on the meta-anisyl ring which on quenching with D<sub>2</sub>O afforded the corresponding 2-deuteride in 80% yield. The 2-iodo analogue was also prepared although in low chemical purity and is a key precursor to new axially dissymmetric bisphosphines containing chiral phosphorus centres. Other approaches to P-chiral ferrocenyl ligands and biaryl ligands are also described and modifications for further development are implicated. An X-ray crystallographic study of six aryl-oxazaphospholidines is also presented and demonstrates the influence of the substituents at phosphorus in determining the conformation of the 1,3,2-oxazaphospholidine ring. A comparison with solution <sup>1</sup>H n.m.r. data showed, in some cases, good correlation between the P-O-C-H dihedral angle and the corresponding solid state torsion angle.

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