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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.
21

Simultaneous construction of axial and planar chirality in the formation of biaryl compounds /

Fogel, Louis E. January 2000 (has links)
Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry. / Includes bibliographical references. Also available on the Internet.
22

Development and application of bifunctional iminophosphorane organocatalysts

Yang, Jinchao January 2016 (has links)
This thesis presents the development and application of bifunctional iminophosphorane (BIMP) organocatalysts, incorporating a triaryl-substituted iminophosphorane organosuperbase for organocatalytic enantioselective reactions. Chapter 2 describes the design and synthesis of a new class of BIMP catalysts and its application in the first organocatalytic enantioselective sulfa-Michael reaction of alkyl thiols to unactivated β-substituted α,β-unsaturated esters. The conjugate adducts were obtained in up to 94% yield and 94% ee. In addition, the reaction was performed on a 1 gram preparative scale with 1 mol% catalyst. Chapter 3 describes the application of BIMP catalysts in the enantioselective desymmetrisation reaction via an intramolecular Michael addition of a pendant pronucleophile to prochiral cyclohexadienone. The high Brønsted basicity of BIMP catalysts was demonstrated in the Michael addition of high pKa pronucleophiles, such as a-substituted malonamate and amide. Chapter 4 describes the application of BIMP catalysts in the challenging Michael addition of malonates to crotonates, cinnamates and methacrylates. For example, the conjugate adduct of malonate and hexafluoroisopropyl cinnamate was achieved in 91% yield and 63% ee in 48 h.
23

Asymmetric aldol reactions and phenylthio migrations in synthesis

Chibale, Kelly January 1992 (has links)
No description available.
24

Investigations into the asymmetric reduction of ketones

Bena, Luvuyo Clifford January 2003 (has links)
A six-step synthesis of salbutamol from methyl salicylate with an overall yield of 17% has been completed, although the yield was not optimised. In the process, Zn(BH4)2 was found to selectively reduce a ketone carbonyl group in the presence of an ester unit. In contrast, borane was found to reduce both the ketone and ester carbonyl groups. Reduction of phenacyl bromide with borane in the presence of chiral catalysts based on (R)-alaninol and (R,S)-ephidrine resulted a measure of enantioselectivity in the product. However, the configuration of the alcohol obtained in the case of (R)-alaninol was contrary to expectations based both on experimental trends observed elsewhere as well as our own theoretical predictions. The asymmetric reduction of methyl 5-bromoacetyl-2-benzyloxybenzoate was accomplished with both borane and Zn(BH4)2 in the presence of a range of chiral catalysts. Optically active products were obtained in all cases, although the optical rotations were significantly smaller in the case of Zn(BH4)2. Unfortunately, we were not successful in determining the enantiomeric excesses of these reactions. The use of a NMR lanthanide shift reagent resulted in a complex spectrum that was impossible to interpret unambiguously. This presumably arises from the presence of several Lewis base sites in the product at which complexation with the shift reagent can take place. It was also not possible to determine the optical rotation of salbutamol itself owing to the relatively small amount of material obtained. A conformational analysis of salbutamol, where NMR data was correlated with molecular modelling results, was successfully carried out and revealed a strong preference for that conformer family characterised by O–C–C–N and Ar–C–C–N torsion angles of ca. 60º and 180º, respectively. Interestingly, these conformers are found to be stabilised by OH…N rather than NH…O hydrogen bonding. This study has also confirmed the effectiveness of the MMFF94 force field for conformational analysis studies in compounds of this kind. Lastly, a relatively simple method for modelling the BH3/oxazaborolidine reduction of ketones at the PM3 semiempirical MO level of approximation was devised. This approach has provided insights into the mechanism of the reaction and has furthermore enabled us to predict the enantioselectivities likely to result from various catalysts and ketones. In comparing our theoretical and experimental findings, an anomalous result was observed in the case of (R)-alaninol; this will have to be investigated further, particularly at the experimental level. However, we believe that our approach provides a sound basis for aiding the design and screening of new, potentially better catalysts.
25

Stereoselective addition reactions of diethylzinc with nitrones, imines and oxime o-ethers

Idris, Musa A. January 1990 (has links)
No description available.
26

Second generation camphor sulfonyl hydrazine (CaSH II) organocatalysis

Li, Qing Hua 01 January 2013 (has links)
No description available.
27

Camphor-derived chiral auxiliaries: a synthetic, mechanistic and computational study

Duggan, Andrew Robert January 2007 (has links)
A broadly based approach has been undertaken to the development and use of camphor derivatives as chiral auxiliaries in asymmetric synthesis – an approach which has embraced synthetic, mechanistic and computational studies. The unambiguous characterization of mono- and dihydroxy-derivatives, obtained by reduction of chiral camphor ether dimers, has been achieved through detailed one- and two-dimensional NMR spectroscopic analysis. The resulting data has been used to establish both the regio- and stereochemistry of the hydroxyl groups. A camphor-derived cyclic iminolactone has been shown to provide a convenient platform for the synthesis of chiral α-amino acids, stereoselective monoalkylation of the iminolactone affording a range of products in yields of 52 - 65 % with up to 85 % d.e. The attempted development of chiral bifunctional Morita-Baylis-Hillman substrates has revealed an unexpected equilibration between isomeric bornane 2,3-diol monoacrylates via acid-catalysed intramolecular transesterification. A detailed [superscript 1]H NMR-based kinetic study of the rearrangement in various media and at various temperatures has permitted the determination of the kinetic and thermodynamic parameters. A computational study at the DFT level has been used to explore the potential energy surfaces of the acid-catalysed and uncatalysed transesterification of the monoacrylate esters. The theoretical data supports the involvement of cyclic intermediates and has provided a rational basis for predicting the favoured reaction pathways. Novel camphor-derived phenyl sulfonate esters and N-adamantylsulfonamides have been synthesised for use as chiral auxiliaries in the Morita-Baylis-Hillman reaction. Modeling at the Molecular Mechanics level has provided useful insights into possible conformational constraints and an adamantyl sulfonate auxiliary has been successfully used in the stereoselective synthesis of a range of products, generally in excellent yield and with up to 95 % d.e.
28

Camphor-derived chiral auxiliaries in asymmetric synthesis

Molema, Warner Evert January 1998 (has links)
The investigation has been focussed largely on the chemistry and stereo-directing potential of camphor-derived compounds. The major regioisomer produced on partial hydrolysis of N-benzylcamphorimide was identified, by one- and two-dimensional NMR and X-ray crystallography, as (+)-(1S,3R)-(N-enzylcarbamoyl)-2,3,3-trimethylcyclopentanecarboxylic acid, the methyl ester of which was shown to undergo an unexpected intramolecular rearrangement during LAH reduction to afford (1S,3R)-Nbenzyl-3-hydroxymethyl-2,2,3-trimethylcyclopentane carboxamide. Several tartrate- and camphor-derived diols have been investigated as chiral auxiliaries in various asymmetric reactions of corresponding acetals of α,β-unsaturated aldehydes. MCPBA epoxidation of the tartrate-derived acetals afforded epoxy acetals in 4-12% diastereomeric excess. The camphor-derived acetals were obtained solely as the exosubstituted diastereomers, the stereochemistry being confirmed by two-dimensional NMR spectroscopy and X-ray crystallography. Simmons-Smith cyclopropanation of these camphor-derived acetals afforded cyclopropyl products with diastereoselectivities of 4% d.e. for the bornane-2,10-diol acetal and 46->99% d.e. for the bomane-2,3-diol acetals. In order to increase diastereofacial selectivity, a camphor-derived diol having a bulky substituent at C-10 was prepared, viz., phenyl 2,3-dihydroxybomane-10sulfonate, and α,β-unsaturated acetals of this diol were shown to undergo Simmons-Smith cyclopropanation with complete topological control (>99% d.e.), the diastereoselectivities being conveniently determined by ¹H and ¹³C NMR spectroscopy. Computer modelling, with the software package HYPERCHEM®, was used to explore the stereochemical aspects of the Simmons-Smith cyclopropanation, and hydrolysis of one of the cyclopropyl acetals has permitted the diastereoselective bias to be confirmed. (+)-Pinane-2,3-diol was also investigated as a chiral auxiliary in the Simmons-Smith reactions of α,β-unsaturated aldehydes, and moderate diastereoselectivities (20-30% d.e.) were observed. In a series of exploratory studies, the Diels-Alder reaction of the 2,3-dihydroxybomane-10-sulfonate acetal of trans-cinnamaldehyde with cyclopentadiene afforded a single cycloadduct, while OSO₄ dihydroxylation, MCPBA oxidation and alkylation of chiral acetals produced from both bomane-2,3-diol and phenyl 2,3-dihydroxybomane-10-sulfonate were less selective.
29

Synthesis and characterization of symmetrical and unsymmetrical ferrocenyl ligands for use in the preparation of Redox Active Ruthenium Alkylidene Complexes

Saku, Duduetsang January 2007 (has links)
Oxidation of a ferrocenyl group in conjugation to another metal centre can alter the electron density at that metal centre and lead to a change in overall reactivity of a complex. Herein, the synthesis and characterization of redox active symmetrical and unsymmetrical ferrocenylalkene derivatives is described. A change in the standard redox potential of ferrocene (465 mV), to more positive potentials in vinylferrocene 1 (478 mV) and 4-phenylvinylferrocene 3 (499 mV), showed how manipulation of a redox potential can be effected on the ferrocenyl moiety by just using conjugation effects. A shift by +13 mV is observed in 1 and this potential more than doubled in 3 (+34 mV). Ferrocenylderived ruthenium alkylidene complexes were also prepared in a cross metathesis of 1 and 3 with Grubbs’ 1 (676.5 mV) to give complexes Ferrocenylidenebis( tricyclohexylphosphine)dichlororuthenium 14, 4-ferrocenylphenylidene-bis (tricyclohexylphosphine)dichlororuthenium 15 respectively. The extent of the electronic communication between the ferrocenyl group and the ruthenium centre was then estimated by looking at the positive or negative redox potential shifts of 14 and 15 as a result of 1 and 3. A large positive potential shift by 180 mV in 14 indicated that there was a strong electronic communication between the two metal centres, while the smaller, yet significant positive potential shift by 89.5 mV in 15 showed 3 to have a lesser effect on the ruthenium centre. Compounds 14 and 15 were tested in a Ring Closing Metathesis (RCM) of diethyldiallylmalonate showed enhanced reactivity.
30

Enantioselective synthesis of oxygenated hydrocarbons by biotransformation

Archer, Ian Victor James January 1996 (has links)
No description available.

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