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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.
91

Development of functionalized spiroligomers for metal-binding and asymmetric catalysis

Xu, Chongsong January 2019 (has links)
This thesis describes the synthesis of functionalized spiroligomers and their applications in metal binding, metal-mediated catalysis, and organocatalysis. By synthesizing a family of functionalized bis-amino acids achieved from reductive alkylation, the Schafmeister group has developed access to highly functionalized and shape programmable structures named “spiroligomers.” The rigid backbones of spiroligomers are good at organizing the orientations of functional groups on their side chains. This property enables them as promising candidates for catalysts. Firstly we synthesized a few spiroligomer dimers presenting metal-binding groups such as terpys and bipys. With the right orientation of metal binding groups controlled by adjusting the stereocenter of the spiroligomer, macrocyclic “square” complexes with metals were obtained. The crystal structures of these intriguing complexes were solved. This work rendered the first structurally, spectroscopically and electronically characterized metal-spiroligomer complexes as well as the first crystal structure of spiroligomer. Secondly, the question of whether metal-binding spiroligomers are able to catalyze certain reactions became our major concern. We developed a binuclear copper catalyst that could accelerate a phosphate ester rearrangement, and that demonstrated that when the two copper binding terpyridine groups were best able to approach each other, they accelerated the rearrangement more than 1,000 times faster than the background reaction. Other molecules that did not properly organize the two copper atoms demonstrate considerably slower reaction rates. At last, catalysts based on spiroligomers without metals are also of interests. By displaying two hydrophobic groups in various directions on a monomeric spiroligomer (also can be regarded as a proline derivative), we observed variable activities and enantioselectivities in the catalysis of asymmetric Michael addition (up to 94% ee at -40 °C for one organocatalyst). / Chemistry
92

Contribution à la synthèse totale de l'alcaloïde (-)-205B / Studies directed towards the total synthesis of Alkaloid (-)-205B

Kamath, Anushree 24 May 2011 (has links)
Une approche hors ‘pool chiral' du système tricyclique 8b-azaacenaphthylène de l'alcaloïde (-)-205B a été développé. Cet alcaloïde, caractérisé par son squelette tricyclique rarement rencontré dans les produits naturels, a suscité un intérêt scientifique important ces dernières années du à son activité biologique potentiel vis à vis de maladies neurodégénératives. Cependant, due à sa très faible bio-disponsibilitié son mode d'action détaillée est actuellement inconnue. Notre stratégie se caractérise par plusieurs transformations remarquables. Une cycloaddition thermique [2 + 2] hautement stéréosélective et une expansion de cycle via un réarrangement de Beckmann donnent accès à un lactame fonctionnalisé. Une réaction de Mannich vinylogue fournit efficacement un buténolide qui est ensuite rapidement transformé en un motif indolizidinone. Après méthylation de cet intermediaire bicyclique, une réaction de cyclisation de type aza-Prins, rarement utilisée en synthèse, conduit à un intermédiaire avancé possédant le système tricyclique qui caractérise le produit naturel. Ainsi, cette approche défini une base solide pour une nouvelle voie d'accès à cet important et particulièrement rare alcaloïde isolé à partir de peau de grenouille néotropicales Dendrobates pumilio considerée comme espèce protégée. / A non-chiral pool approach to the 8b-azaacenaphthylene ring system of the frog poison alkaloid (-)-205B has been developed. This rare tricyclic alkaloid has been of considerable synthetic interest in recent years owing to its potential biological activity against neuronal disorders. However, due to lack of material, a detailed study of the mode of action of this natural product has not yet been reported. Our strategy features several noteworthy transformations. A highly diastereoselective thermal [2+2] cycloaddition and a ring expansion through Beckmann rearrangement generates the functionalised lactam intermediate. An efficient vinylogous Mannich reaction then provides access to a butenolide, which subsequently leads to an indolizidinone ring system. After installation of a methyl group on this bicyclic intermediate, a relatively unexplored aza-Prins cyclization has been successfully employed to obtain an advanced intermediate, possessing the desired tricyclic system found in the natural product. This approach has laid a solid foundation for a novel access to this potentially important but scarce alkaloid extracted from a neotropical frog Dendrobatus pumilio that is threatened to be endangered.
93

Synthesis of rare sugars and novel sugar derivatives from 1,2-dioxines.

Robinson, Antony Vincent January 2008 (has links)
1,2-Dioxines are a specific class of cyclic peroxide that are both prevalent in nature and important synthetic building blocks. To date, much of the chemistry involving 1,2-dioxines is concerned with cleavage of the weak peroxide bond, providing a convenient method for the incorporation of 1,4-oxygen functionality into molecules. Comparatively little attention has been directed towards transformations of the alkene unit contained within 1,2-dioxines, which is the focus of this thesis. The synthesis of a broad range of diversely functionalised 1,2-dioxines from commonly available starting materials is presented. Subsequently, the osmium catalysed dihydroxylation of 3,6-disubstituted 1,2-dioxines was investigated, furnishing novel peroxy diols in high yield and with excellent diastereoselectivity. The peroxy diols were then reduced, affording stereospecific tetraols and higher polyols, including the rare sugar allitol. In addition, homolytic ring-opening of the 1,2-dioxanes was examined, providing a new route to polyhydroxylated furanoses, highlighted by the synthesis of the natural keto-sugar psicose. Several 4-substituted 1,2-dioxines were also dihydroxylated, followed by reduction of the peroxide bond, providing a convenient route to branched erythritol derivatives, including the important plant sugar 2-C-methyl-erythritol. The cobalt catalysed ring-opening of the peroxy diols produced novel erythrose derivatives in high yield. In addition, the triphenylphosphine induced ring contraction of the peroxy diols is presented, which allowed for the synthesis of novel dihydroxylated tetrahydrofurans in excellent yield. Asymmetric dihydroxylation of the achiral 4-substituted 1,2-dioxines was explored, furnishing optically enriched peroxy diols with varying enantioselectivity depending on the substrate. The synthesis of novel alkyl and aryl branched erythrono-γ-lactones via oxidation of lactols derived from the acetonide protected peroxy diols is also documented. The utility of this sequence is illustrated by the preparation of potassium 2,3,4-trihydroxy-2-methylbutanoate, a leaf-closing substance of Leucaena leucocephalam. Additionally, γ-lactones were prepared from epoxy hydroxy ketones derived from epoxy-1,2-dioxanes, facilitated by a Baeyer-Villiger lactonisation protocol. The requirements and limitations of this procedure are discussed. The proposed and attempted synthesis of other lactones from 1,2-dioxines was also examined. Finally, several other general alkene transformations were investigated on 1,2- dioxines including: halo-hydrin formation, phenylselenyl chloride addition, aminohydroxylation, cyclopropanation, and aziridination, allowing for the preparation of several new classes of functionalised 1,2-dioxines. In summary, the work presented in this thesis establishes clear and efficient methodology towards several interesting and useful sugar-type core structures from modified 1,2-dioxines. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1313493 / Thesis (Ph.D) -- University of Adelaide, School of Chemistry and Physics, 2008
94

Enzyme- and Transition Metal-Catalyzed Asymmetric Transformations : Application of Enzymatic (D)KR in Enantioselective Synthesis

Lihammar, Richard January 2014 (has links)
Dynamic kinetic resolution (DKR) is a powerful method for obtaining compounds with high optical purity. The process relies on the combination of a kinetic resolution with an in situ racemization. In this thesis, a combination of an immobilized hydrolase and a transition metal-based racemization catalyst was employed in DKR to transform racemic alcohols and amines into enantioenriched esters and amides, respectively. In the first part the DKR of 1,2-amino alcohols with different rings sizes and N-protecting groups is described. We showed that the immobilization method used to support the lipase strongly influenced the stereoselectivity of the reaction. The second part deals with the DKR of C3-functionalized cyclic allylic alcohols affording the corresponding allylic esters in high yields and high ee’s. The protocol was also extended to include carbohydrate derivatives, leading to inversion of a hydroxyl substituted chiral center on the carbohydrate. The third part focuses on an improved method for obtaining benzylic primary amines. By using a novel, recyclable catalyst composed of Pd nanoparticles on amino-functionalized mesocellular foam, DKR could be performed at 50 °C. Moreover, Lipase PS was for the first time employed in the DKR of amines. In the fourth part DKR was applied in the total synthesis of Duloxetine, a compound used in the treatment of major depressive disorder. By performing a six-step synthesis, utilizing DKR in the enantiodetermining step, Duloxetine could be isolated in an overall yield of 37% and an ee &gt;96%. In the final part we investigated how the enantioselectivty of reactions catalyzed by Candida Antarctica lipase B for δ-substituted alkan-2-ols are influenced by water. The results showed that the enzyme displays much higher enantioselectivity in water than in anhydrous toluene. The effect was rationalized by the creation of a water mediated hydrogen bond in the active site that helps the enzyme form enantiodiscriminating binding modes. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>
95

Rh-catalyzed asymmetric C-H bond activation by chiral primary amine

Taleb Sereshki, Farzaneh 03 February 2017 (has links)
Developing asymmetric C-H bond activation methods in order to achieve enantiopure products is crucial for the advancement of the field and for the production of novel chiral compounds. Therefore, we tried to develop this area of organic chemistry by presenting metal catalyzed stereoselective C-H bond activation utilizing chelation-assisted tools. The first section of this study involves Rh(I) catalyzed asymmetric C-H bond activation of a series of ketones via an intermolecular procedure. By this method, we examine ortho-alkylation of aromatic ketones and β-functionalization of α-β unsaturated ketones with a series of prochiral olefins. In the second section, we present an efficient three steps method for stereoselective intramolecular C-H bond activation of indol-3-carboxaldehyde with tethered prochiral olefins. The catalytic system in both methods involves a joint chiral primary amine and Rh(I) catalyst. Chiral primary amines can serve to induce enantioselectivity as well as acting as a useful directing group which has shown appropriate coordination to the transition metal catalyst, providing high regioselectivity. / February 2017
96

Chiral phanephos derived catalysts and their application in asymmetric catalysis

Konrad, Tina Maria January 2013 (has links)
The research presented in this thesis is a project funded by the EU-network of the Marie Curie project NANO-HOST in collaboration with partner institutes. The aims of this network are to develop innovative methods for the preparation, recovery and reuse of single-site, nanostructured catalytic materials, and further on apply them in combination with specifically engineered reactors for a sustainable production process for making high value fine chemicals. One part of this project was to prepare chiral diphosphine ligands and their complexes for currently challenging reactions, such as asymmetric carbonylations (homogeneous catalysis). Catalytic studies of these chiral diphosphine ligands were carried out in asymmetric hydroxy-and alkoxy-carbonylations and hydrogenation reactions. The second part of this project was the heterogenisation of these chiral homogeneous complexes through collaborations with the network partners and furthermore their catalytic behavior was studied.
97

Asymetrická organokatalytická syntéza organických sloučenin z α,β-nenasycených aldehydů / Organocatalytic asymmetric synthesis of various organic compounds from α,β-unsaturated aledyhes

Kamlar, Martin January 2010 (has links)
With regard to a fast development in the field of fluoroorganic chemisty, the intention of this diploma thesis is focused to utilize of organocatalysis by secondary amines as catalysts for preparation enantiomerically pure compounds containing fluorine atom in its structure. The preparation of these subsances is realized by way of nucleofilic addition to α,β- unsaturated aldehydes using suitable fluorine containing nuclephilic agent 1-(fluoronitromethylsulphonyl)benzene, to get appropriate 1,4-adduct.
98

Synthesis and resolution of novel chiral pyridylphenols and their applications in catalytic asymmetric addition of diethylzinc to aldehydes.

January 1996 (has links)
by Huichang Zhang. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 114-130). / Acknowledgment --- p.i / Abstract --- p.ii / Abbreviations --- p.iii / Table of Contents --- p.iv-v / Chapter Chapter I --- Introduction --- p.1 / Chapter I --- The basis of asymmetric catalysis --- p.6 / Chapter II --- Chiral catalyst --- p.8 / Chapter II-I --- Center metal --- p.9 / Chapter II-II --- Chiral ligand --- p.10 / Chapter III --- Structural analysis of effective chiral ligands --- p.13 / Chapter III-I --- Monodentate ligand --- p.15 / Chapter III-II --- Bidentate Ligand --- p.16 / Chapter 1 --- Bidentate phosphine ligand --- p.16 / Chapter 2 --- Bidentate oxygen ligand --- p.17 / Chapter 3 --- Bidentate nitrogen ligand --- p.19 / Chapter 4 --- "Bidentate ligand with N, 0,P, or S donor atom" --- p.21 / Chapter III-III --- Potentially tridentate ligand --- p.22 / Chapter III-IV --- Potentially tetradentate ligand --- p.23 / Chapter IV --- Tentative conclusions on the effect of structural elements --- p.24 / Chapter Chapter II --- "Design, synthesis and resolution of novel chiral pyridylphenols" --- p.27 / Chapter I --- Design of chiral ligand --- p.27 / Chapter II --- Synthesis of chiral ligands --- p.29 / Chapter II-I --- "Synthesis of the chiral N, O-donor ligands" --- p.29 / Chapter 1 --- Synthesis of the chiral ligands 75a-75c --- p.29 / Chapter 2 --- Synthesis of the chiral ligands 93a and 93b --- p.37 / Chapter 3 --- Synthesis of the chiral ligands 97a-97c --- p.41 / Chapter II-II --- "Synthesis of the chiral N, P-donor ligand 98 and N, S-donor ligand 101" --- p.42 / Chapter III --- Resolution of racemates of chiral ligands --- p.44 / Chapter III-I --- Resolution of of the pyridylphenol 75b --- p.44 / Chapter III-II --- Resolution of of the pyridylphenol 93a --- p.48 / Chapter III-III --- Racemization study of 75b and 93a --- p.52 / Chapter 1 --- Racemization test of 75b --- p.52 / Chapter 2 --- Racemization test of 93a --- p.52 / Chapter Chapter III --- Asymmetric addition of diethylzinc to aromatic aldehydes catalyzed by chiral pyridylphenols / Chapter I --- Backgound --- p.53 / Chapter II --- Asmmetric addition of Et2Zn to aldehydes catalyzed by chiral pyridylphenols --- p.61 / Chapter II-I --- Asmmetric addition of Et2Zn to aldehydes catalyzed by (R)-(+)-75b --- p.61 / Chapter 1 --- The influence of the solvent --- p.61 / Chapter 2 --- The influence of the reaction temperature --- p.64 / Chapter 3 --- The influence of the concentration of catalyst --- p.66 / Chapter 4 --- Electronic effect on the enantioselectivity of asymmetric addition of Et2Zn to aromatic aldehydes --- p.67 / Chapter II-II --- Asmmetric addition of Et2Zn to aldehydes catalyzed by (5)-(+)-75b --- p.73 / Chapter II-III --- Asmmetric addition of Et2Zn to aldehydes catalyzed by (R)-(+)-93a --- p.75 / Chapter III --- Conclusions --- p.78 / Chapter Chapter V --- Experimental Section --- p.79 / References --- p.114 / NMR Spectra --- p.131
99

Novel palladium catalyzed phosphination using triarylphosphines: synthesis of atropisomeric P,N ligands and their application in asymmetric hydroboration. / CUHK electronic theses & dissertations collection

January 2000 (has links)
by Fuk Yee Kwong. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2000. / 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.
100

Biocatalytic imine reduction and reductive amination

France, Scott January 2018 (has links)
Chiral amine motifs are found in many bioactive compounds and therefore strategies for their direct asymmetric synthesis are of great interest. Alongside traditional chemical methods, biocatalysis serves as an important tool for the formation of these compounds that can confer the benefits of sustainable catalyst supply and mild reaction conditions. This thesis describes the application of imine reductase (IRED) biocatalysts for the asymmetric reduction of pre-formed imines and the reductive amination of carbonyl compounds to produce chiral amines. These enzymes are relatively recent additions to the toolbox of biocatalysts for chiral amine synthesis and therefore their scope and application is still very much being explored. The research carried out as part of this PhD is presented as a series of manuscripts that have either been published or are planned for submission to peer-reviewed journals. The choice of presenting this thesis in journal format was made because a considerable body of the candidate's PhD research has been published, with the rest planned for publication in the near future. Furthermore, the compiled review articles and research papers lend themselves to a clear thesis narrative and, combined, have taken considerable time and effort to prepare, equal to that of a traditional thesis format. The contents are organised as follows: Chapter 1: an introduction to biocatalysis and its impact on sustainable chemical manufacturing; Chapter 2: a review assessing the current state of the art in imine reductase biocatalysts; Chapter 3: a perspective on the design and implementation of biocatalytic cascades; Chapter 4: a research article on the application of IREDs in a biocatalytic cascade for the synthesis of chiral piperidine and pyrrolidine frameworks; Chapter 5: aims of the PhD project; Chapter 6: a research article on the discovery and investigation of a reductive aminase (RedAm) found within the IRED family; Chapter 7: a research article on the screening of a diverse set of novel IREDs for their ability to facilitate reductive amination; Chapter 8: a research article on the synthesis of complex bulky dibenz[c,e]azepine compounds using IRED and transaminase biocatalysts; Chapter 9: a summary and outlook; Chapter 10: manuscript supporting information further detailing experimental work; Appendix: list of other publications resulting from this doctoral research.

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