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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.
1

Reacciones de Friedel-Crafts enantioselectivas catalizadas por complejos de metales de transición del grupo (IV) y binol

Vila Descals, Carlos 23 July 2010 (has links)
La reacción de Friedel-Crafts es un poderoso proceso de formación de enlaces carbono-carbono de gran importancia en síntesis orgánica. La aplicación de la versión asimétrica catalítica de esta reacción a la alquilación de arenos ricos en electrones, como indoles o pirroles, puede proporcionar acceso a importantes productos enantioméricamente enriquecidos alquilados y constituyen un tema de actual interés, ya que estos arenos se han identificado como estructuras "privilegiadas" o farmacóforos. Los complejos Zr(IV) y Hf(IV)-BINOL generados in situ han sido evaluados como catalizadores en la alquilación de Friedel-Crafts enantioselectiva de indoles y pirroles con diferentes cetonas α, β-insaturadas, así como en la alquilación de pirroles con diferentes tipos de los compuestos carbonilícos. Para la alquilación de Friedel-Crafts enantioselectiva de indoles con simples cetonas α,β- insaturadas no quelatantes se han utilizado como catalizadores complejos Zr(OtBu)4-(R)-3,3'-Br2-BINOL (L3) generados in situ. La reacción se lleva a cabo con muy buenos rendimientos (hasta 97%) y buena enantioselectividad (hasta 98% ee). Para hacerse una idea de la estructura del catalizador y los aspectos mecanísticos de la reacción, se investigó los espectros de RMN 1H del catalizador, así como experimentos de efectos no lineales (NLE) y estudios computacionales (DFT). La alquilación de Friedel-Crafts de pirroles con simples cetonas α,β- insaturadas no quelatantes. catalizada por Zr(OtBu)4-(R)-3,3'-Br2-5,5',6,6',7,7',8,8'-BINOL, da lugar a pirroles alquilados con buenos rendimientos y enantioselectividades de moderadas a muy buenas. También se ha desarrollado una estrategia eficaz para acceder a derivados de indol 2-sustituidos de forma enantioenriquecida. Esta estrategia se basa en una reacción catalítica asimétrica “one-pot” de Friedel-Crafts entre 4,7-dihidroindol y cetonas α,β-insaturadas, seguida de una oxidación de p-benzoquinona, utilizando el complejo Zr(OtBu)4-L5 dando lugar a buenos rendimientos y enantioselectividades moderadas. Las cetonas -trifluoro ,-insaturadas- se han utilizado como electrófilos en la alquilación de Friedel-Crafts enantioselectiva de indoles catalizada por el complejo Zr(OtBu)4-(R)-3,3'-Br2-BINOL (L3), proporcionando una variedad de indoles trifluorometilados quirales con buenos rendimientos (hasta 99%) y excelentes enantioselectividades (hasta 99% ee). (E)-1-aril-4-benciloxi-but-2-en-1-onas también pueden ser utilizadas como electrófilos en la reacción de Friedel-Crafts de indoles catalizada por el complejo Hf(OtBu)4-(R)-3,3'-Br2-BINOL (L3) para obtener indoles quirales con una cadena 1,4-funcionalizada. Los rendimientos y enantioselectividades van de buenos a excelentes para una gama de diferentes benciloximetilenonas y indoles. La alquilación de Friedel-Crafts de indoles con (E)-1,4-diaril-but-2-en-1,4-dionas catalizadas por complejos quirales de Hf(OtBu)4-(R)-6,6'-Br2-BINOL (L2) genera un centro estereogénico en  con respecto a uno de los grupos carbonilo. Esto puede considerarse como una inversión del patrón de reactividad normal o umpolung. La reacción se lleva a cabo con buenos rendimientos (hasta un 97%) y buenas enantioselectividades (hasta un 94%), independientemente de la naturaleza y la posición de los sustituyentes en las endionas o en el anillo de indol. Los (E)-4-oxo-4-fenilbutenoatos de alquilo también se han utilizado como electrófilos en la alquilación de Friedel-Crafts enantioselectiva de indoles utilizando el complejo Zr(OtBu)4-(R)-3,3'-Br2-BINOL (L3) como catalizador. En este caso, se forma el centro estereogénico en posición  al éster regioselectivamente, con buenos rendimientos y enantioselectividades. Se ha utilizado el complejos Zr(OtBu)4-(R)-3,3'-Br2-BINOL (L3) como catalizador la alquilación de Friedel-Crafts de pirroles con una variedad de diferentes 2,2,2-trifluoroacetofenonas para dar lugar a alcoholes terciarios teniendo un centro estereogénico cuaternario. La reacción tiene lugar con buenas enantioselectividades (hasta un 93% de ee) y excelentes rendimientos (hasta un 99%). También se ha descrito la alquilación de Friedel-Crafts de diferentes derivados de pirrol con una variedad de -cetoésteres catalizada por complejos Zr(OtBu)4-(L6) para dar lugar alcoholes terciarios con diferente sustituido enantioselectividades muy buena (hasta un 98% ee) y buenos rendimientos (hasta 79%). El 4,7-dihidroindol también se puede utilizar como nucleófilo en la alquilación de Friedel-Crafts con -cetoésteres, seguida de una oxidación de p-benzoquinona proporcionando derivados de indol 2-sustituidos, en un sencillo procedimiento “one-pot”. / The Friedel-Crafts (F-C) reaction is a powerful carbon-carbon bond forming process of great importance in organic synthesis. The application of the asymmetric catalytic version of this reaction to the alkylation of electron-rich arenes, such as indoles or pyrroles, can provide access to important enantiomerically enriched alkylated arene products and constitute a topic of ongoing interest, due that this arenes have identified as “privileged” structure or pharmacophore. In this Thesis Zr(IV) and Hf(IV)-BINOL complexes generated in situ have been evaluated as catalysts in enantioselective F-C alkylation of indoles and pyrroles with different α,β-unsaturated ketones, as well as in the alkylation of pyrroles with different kind of carbonyl compounds. Zr(OtBu)4-(R)-3,3'-Br2-BINOL complexes have been used as very effective catalysts for the enantioselective F-C alkylation of indoles with simple non-chelating α,β-unsaturated ketones. The reaction takes place with very good yields (up 97%) and good enantioselectivity (up 98% ee). The Friedel-Crafts alkylation of pyrroles with simple non-chelating α,β-unsaturated ketones catalyzed by Zr(OtBu)4-(R)-3,3'-Br2-5,5',6,6',7,7',8,8'-BINOL give the products with good yields and moderate to very good enantioselectivities. 2-Substituted indole derivatives were synthetized by one-pot catalytic asymmetric Friedel-Crafts reaction between 4,7-dihydroindole and α,β-unsaturated ketone, followed by a p-benzoquinone oxidation, with good yields and moderated enantioselectivities. The -unsaturated -trifluoroketones have been used as electrophiles in the enantioselective F-C alkylation of indoles catalyzed by BINOL complex, providing a variety of trifluoromethylated chiral indoles in good yields (up 99%) and excellent enantioselectivities (up 99% ee). (E)-1-aryl-4-benzyloxy-2-buten-1-ones, (E)-1,4-diaryl-2-butene-1,4-diones and (E)-4-oxo-4-phenylbutenoates can also be used as electrophiles in the F-C reactions of indoles catalyzed by the BINOL complex to obtain chiral indoles with a 1,4-difunctionalized moiety. Zr(OtBu)4-(R)-3,3'-Br2-BINOL catalyst has been used in a F-C alkylation of unprotected pyrrole with a variety of differently substituted 2,2,2-trifluoroacetophenones to give pyrroles with a trifluoromethyl substituted tertiary alcohol moiety bearing a quaternary stereogenic center. The reaction takes place with good enantioselectivities (up to 93% ee) and high isolated yields (up to 99%). Chiral complex of Zr(OtBu)4-(R)-3,3'-bis(3,5-bis(trifluoromethyl)phenyl)BINOL has been used as a catalyst in a F-C alkylation of different pyrrole and 4,7-dihidroindole derivatives with a variety of differently substituted -ketoesters to give tertiary alcohols with very good enantioselectivities (up to 98% ee) and good yields (up to 79%).
2

Bichromophoric molecules as absolute standards for the triplet sensitised production of singlet oxygen

Forward, Philip James January 1995 (has links)
A series of bichromophoric molecules containing aromatic ketone and hyrocarbon residues linked by a chain of two methylene groups were prepared by chemical synthesis. Time-resolved photochemical experiments using kinetic emission and absorption spectroscopy were carried out to evaluate the bichromophoric compounds for use as reference standards for the triplet sensitised production of singlet oxygen in organic and aqueous solvents. The efficiency of singlet oxygen formation was found to vary considerably with solvent A comprehensive photophysical study was performed on phenalenone to investigate its potential as a universal reference standard for singlet oxygen formation in both organic and aqueous media. Singlet oxygen yield data were obtained from experiments in benzene which conflicted with recently published work. The experiments also led to the calculation of an accurate value for the molar absorption coefficient of the triplet state of benzophenone in benzene. Time-resolved infrared luminescence detection was employed in an attempt to quantify the possible effect of the substituent group on the observed yield of singlet oxygen from several naphthalene derivatives relative to naphthalene, for which a value of unity, from data using various experimental techniques, has been published. A series of substituted naphthalenes were found to have singlet oxygen yields which were experimentally indishtinguishable from that of naphthalene and were therefore taken to be unity.
3

Development of a commercial process to produce 1,4-butanediol and tetrahydrofuran

Wood, Michael Anthony January 2009 (has links)
This thesis details the experimental programme and research into the formation of 1,4-butanediol and tetrahydrofuran from a novel feedstock dialkylmaleate. This encompassed the evaluation of a range of heterogeneous copper-based catalysts (containing chromium) and subsequent selection and optimisation of one of these catalysts for extended life time studies and eventual use in a commercial facility. The selected operating conditions (temperature of 190 - 205 ºC, pressure 885 psi[g]) ensured that the reaction was performed in the vapour-phase at moderate temperature and pressure to maximise the yield of the main product 1,4- BDO (>95%) and THF (<5%). The thesis details the development of several variants of non-chromium containing Cu-based catalysts, which then enabled a multi-variable product process to be realised. The selection of operating conditions further enhanced the flexibility of the process by operating at temperatures in the 205 - 220 ºC range to increase the selectivity to THF (50 - 95%) responding to changing market conditions. The development of both process options encompasses initial testing, screening and ultimately optimisation of the catalysts using laboratory-based reactors generating data that was suitable for commercial design. The catalysts generated were shown to produce 1,4-BDO and THF over extended periods from the preferred feedstock; dialkylmaleate. The thesis also outlines the importance of the pre-treatment of the catalyst for use in a vapour-phase hydrogenolysis process and that this is a key consideration in achieving any commercially viable process. The operation of the carefully pre-treated catalyst in the vapour-phase enabled a highly efficient process to be developed in the laboratory environment generating design data for commercial facilities, in which all of the development steps were later confirmed in commercial operations in several countries. The development of a solid acid catalyst, used to catalyse the conversion of an acid to ester, is detailed. The ion-exchange resin used as the catalyst was optimised to minimise the main by-products by structuring acid sites on the surface of the solid support only. This enabled high conversions of the acid >99 wt% to be achieved at low temperatures in the region of 95 - 120 ºC, which was an extremely efficient process. The subsequent design and development of a unique reactor for the esterification of the acid species is also outlined in this thesis. The reactor, which is based on a counter-current reactive distillation concept, enabled maximum utilisation of the solid acid catalyst developed and is also reported. This aspect of the thesis involved not only studying the chemical transformation but also a detailed study of the fluid dynamics that would be present in the commercial reactor; this encompassed the build and operation of several cold flow models evaluating not only gas distribution but liquid/resin movement in the reactor. The combination of the two transformations gave a world leading technology to convert maleic anhydride to 1,4-BDO and THF. The work reported in this thesis Is the basis on which further testwork, in both the hydrogenation and esterification, is performed. These process improvements are being researched to ensure the technology remains one of the main manufacturing routes to produce 1,4-BDO and THF from a diaikylmaleate feedstock.
4

Electrophilic fluorination of ethers and deactivated benzene derivatives

Trmcic, Jelena January 2005 (has links)
Chapter 1 - Chapter 1 provides a literature review of the relevant topics for this thesis in organofluorine chemistry: effect of fluorine as a substituent on the molecule, synthesis of C-F bond from C-H bond using electrophilic reagents with discussions of mechanisms. Chapter 2 ― Direct fluorination of electron-rich systems such as alkyl and cyclic saturated ethers using elemental fluorine results in the formation of unexpected products: fluorinated aldal acetáis. Selectfluor™ was also used to prepare these products in good yield, but also to gain information about mechanism. Chapter 3 - Same methodology for fluorination of deactivated benzene derivatives using elemental fluorine was applied and resulted in a selective substitution of hydrogen by fluorine and allowed the synthesis of a diverse collection of polyfunctional monofluorinated aromatic products. Chapter 4 - Fluorination of 1,3- and 1,4-disubstituted benzaldehyde derivatives was studied in the reactions with elemental fluorine and resulted usually in mixtures of two products. It is concluded that the distribution of the two competing products is dependent on the total electric effect of the substituent (σ-value) attached to the aromatic ring. Chapter 5 - Our research group has developed a microreactor for the purpose of selective fluorination of a wide range of compounds such as benzaldehydes and nitrobenzenes. Low inventories of fluorine gas, in contact with reagents, provide increased safety. Optimization was obtained by varying substrate flow rate, and often resulted in a good conversion and superior yields. Chapter 6-9- Experimental details of the work discussed in Chapters 2-5.
5

Structure-property relationships in framework materials : anomalous mechanics by design

Collings, Ines E. January 2014 (has links)
Framework materials that contain molecular bridging ligands between metal nodes-as seen in coordination polymers-not only give rise to enhanced structural diversity, but also to a range of useful and unusual mechanical properties. This thesis demonstrates the general structure-property relationships that are developed for coordination polymers in order to enable prediction and design of their mechanical properties, and hence structural flexibility. Variable-temperature and -pressure diffraction experiments are employed for the determination of their mechanical properties, namely by calculating thermal expansion and compressibility coefficients. The anomalous and varied mechanical responses observed are rationalised by the important structural features, or the so-called mechanical building units (XBUs), of the coordination polymers. The XBUs are considered within the setting of framework topology, geometry, and composition in order to establish general design principles for targeting different degrees of flexibility within coordination polymers. The XBUs are identified first in silver(I) 2-methylimidazolate, Ag(mim), a framework which is comprised of structural motifs of varying strength, namely argentophilic interactions, hinge points and metal- ligand bonding. The anomalous mechanical responses in Ag(mim) are shown to be rationalised entirely by the XBUs present in the structure. The XBU abstraction is then applied to a range of other coordination polymers and shown to correspond directly with the anomalous responses known in these materials. The metal-ligand-metal linker XBU is investigated further in both cadmium imidazolate, Cd(imh, and zinc cyanide, Zn(CN)2. Here, the linker chemistries are completely different between the two frameworks, but the diamondoid arrangement of the linkers, and thus the topology, is the same. The structural responses of the two frameworks are examined to unravel the extent of topology- and chemistry-driven mechanics. It is found that the topology dominates the atomic displacements of both frameworks, indicating the existence of common soft-mode dynamics which are likely to extend to other coordination polymers with the same topology. The three-dimensional framework-hinging XBUs in zinc isonicotinate, Zn(ISNh, and indium deuterium terephthalate, InD(BDCh, are considered next. These frameworks have the same topology but contrasting framework geometries, evident from the differing cia-lattice parameter ratios. In this case, a geometric formalism is derived which can predict the direction of framework mechanical anisotropy in Zn(ISNh and InD(BDCh and other uniaxial coordination polymers. Finally, a family of ABX3-type transition metal(II) formates are investigated, where both the B-site and A-site cations are varied. The chemical modifications give rise to variations in B- or A-site cation sizes, which are found to correlate with the magnitude of mechanical responses. These structure-mechanical property relationships-based upon framework topology, geometry and composition- are presented in separate chapters, and in each case generalised so that they can be applied to a range of coordination polymers. Hence the' design principles determined here can provide the materials science community with an intuition on the type and magnitude of responses possible in these materials under different external stimuli.
6

Synthetic tools for carbohydrate-protein interaction studies

Fourniere, Viviane January 2013 (has links)
Carbohydrate-protein interactions are important for the tuning of many biological processes. Tools are required to investigate the carbohydrate recognition domains. Several examples are presented in this work. The first project consists in the synthesis of neoglycoconjugates for binding studies. Here a simple and efficient route to functionalise chitobiose, chitotriose and chitotetraose with a suitable linker avoiding protecting group chemistry is described. Unprotected chitooligomeres were used as starting material. After amination of the anomeric position of the saccharides, the linker was attached by amide formation. An amide bond was chosen to mimic the peptide bond. Two projects discuss the synthesis of a pentasaccharide and a heptasaccharide. Using as many identical building and reactions as possible in both the synthesis, the oligosaccharides was assembled following a linear pathway. For the pentasaccharide synthesis, a convergent pathway was attempted first. Starting respectively with a monosaccharide or a disaccharide, each sugar was added after the other, usually followed by a protecting group manipulation. Experience gained during the pentasaccharide synthesis for protecting group manipulation, strategic group pattern and glycosylation was used for the heptasaccharide synthesis. 1,2-cis glycosylation was improved via a new one-pot procedure. At the end, a hydrogenolysis provided the fully deprotected target molecule. The last project deals with selenoglycosides. They are intended to improve structure elucidation of lectins by X-Ray crystallography-: Since both 0 and 13 selenoglycosides are of interest, a route to the two anomers using a common precursor was investigated. The l3-selenoglycosides of common mono- and disaccharides were prepared. The respective glycosyl halides were added to the "in situ" reduced dimethyldiselenide. The anomerisation of the 13 anomers were performed using BF3· OEt2. This route was applied on a H1/Lewisb determinant as well. The major problem in this part of the project was to obtain the β orientation of the selenomethyl group without using a participating group. A solution was eventually found by employing a large excess of the reducing agent during the introduction of the seleno group as a smaller excess led to an α/β mixture.
7

New approaches towards the total synthesis of macrocyclic bisbenzyl natural products

Murgues, Paul Gabriel January 2013 (has links)
The macrocyclic bisbibenzyls are a family of natural products generally extracted from species of liverworts. They have attracted considerable attention from synthetic chemists as they display an interesting array of biological activities. Furthermore, as each contains a strained cyclophane core, they present an interesting challenge to the synthetic chemist. Many total syntheses have been published, but to date no general strategy based on robust conditions has been established. The thesis describes our attempts to establish such an approach for the synthesis of the macrocyclic bisbibenzyl family of natural product. The discussion is divided in two independent parts. The first approach described sought to generalise an existing approach that had proven successful for the synthesis of a few macrocyclic bisbibenzyl natural products. A key of that strategy was the use of palladium-catalysed cross-coupling reactions to unite key fragments. The synthetic plan was redesigned for the general case and rationalised in light of difficulties reported in the existing literature. Over 20 potential coupling precursors were synthesised in a few high-yielding steps and their behaviour examined in Suzuki-Miyaura cross-coupling reactions using various reaction protocols. A suitable combination of precursors and catalyst was found to afford many of the desired biaryl products in high yields, though further investigation is required to advance these to the natural product targets. The second strategy was based on a bidirectional approach and a biomimetic ring closure. The synthesis of acyclic precursors by means of Sonogashira and Heck couplings gave disappointing results. The use of Wittig olefination provided an excellent synthetic route to the required bisbibenzyl macrocyclisation precursors. Alas, none of the envisioned macrocyclisation reactions succeeded.
8

The synthesis of rationally designed donor-acceptor dyads incorporating the boron dipyrromethene fluorophore

Clift, Sophie January 2013 (has links)
This thesis is concerned with the design, synthesis, characterisation and subsequent photophysical examination of dyads incorporating the boron dipyrromethane (bodipy) framework. Photodriven processes such as electron-, energy- and charge-transfer reactions are of the utmost importance in nature, with photosynthesis as a key example. Energy capturing arrays composed of intricate building blocks trap, transfer and store energy within a cell, employing a complex series of cascade-type reactions to channel this energy to the desired acceptor. Within this thesis, the theme of charge-transfer in particular is of principal focus and systems designed to investigate this phenomenon are examined. Chapter one presents an introduction to the bodipy fluorophore and the everexpanding field of artificial photosynthesis. In addition to this, the methods involved in analysing the distribution and movement of charge are discussed, as are the thought processes behind the rational design of molecules for specific functions. The second chapter serves as a detailed account of all the synthetic procedures undertaken. The chapter covers all the bodipy derivatives prepared, in addition to the precursors to these compounds and all additional materials synthesised. In chapters three to six, the rationale behind the design of each purpose built system is discussed, along with any preparative difficulties encountered and modifications to traditional synthetic protocol. Finally, the electrochemical properties of the compounds are analysed by cyclic voltammetry and their photophysics investigated by absorption and fluorescence spectroscopy. The data obtained is complimented by both appropriate NMR spectra and a discussion of crystal structural information obtained. In the case of the novel push-pull chromophore, JULBD, which is the principal focus of chapters three and four, the charge transfer capabilities of the dyad are analysed by correlating 13C chemical shift values with solvent polarity. This polarity dependence is further explored and analysed by solvent dependent absorption spectroscopy. In ii order to study the emissive properties, a temperature dependent fluorescence experiment was undertaken. Chapter five discusses the use of current catalytic methods to prepare a series of novel donor acceptor dyads and their precursor building blocks, introducing novel methodology for the synthesis of boronic esters including iridium and palladium catalysis. Finally, chapter six addresses the design rationale, synthesis and characterisation of a binaphthalene-spaced dyad incorporating the N,N-dimethylaniline moiety. This chapter also serves to introduce novel methodology which can be employed to execute bodipy sythesis employing the commonly used organic reagent formamide.
9

Protecting group free approaches to the synthesis of stemona alkaloids

Connelly, Rickki L. January 2013 (has links)
No description available.
10

Collinear laser spectroscopy of the 178Hf S- isomer and the 18<>-ra naturally occurring isomer

Lloyd, Bissell January 2007 (has links)
The work presented in this thesis was conducted as part of an ongoing investigation into the properties of multi quasiparticle isomers. Specifically, collinear laser spectroscopy was perfonned on singly ionized 178Hf. Laser induced fluorescence spectra of the 301.3 nm transition were recorded from which the isomer shift between the 178Hf ground state and the r=s- isomer was obtained along with the hyperfine structure associated with this isomer, With these measurements it was possible to detennine the change in mean square charge radius between the ground state and isomer and also its magnetic and elec;:trostatic quadrupole moments. The observed properties of this isomer have been used in conjunction with measurements ofother isomeric systems to explore the origins of the decrease in charge radii of multi quasi-particle isomers, a phenomenon observed in all systems ofthis type measured to date. With the objective of extending this work on the properties ofmulti quasi-particle isomers, off-line measurements of transitions in singly charged Ta were conducted. Strong second order contributions to the hyperfine structures were observed. With a full description of these contributions, it was possible to unambiguously detennine the spin of the 18<>-ra naturally occurring isomer along with its magnetic and electrostatic quadrupole moments.

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