No description available.

No description available.

No description available.

The "modified triester" and phosphodichloridite procedures for oligoribonucleotide synthesis, using 2'- silylated nucleosides, were compared. Phosphodichloridite reagents were faster and more efficient than the arylsulphonyl reagents for both dinucleotide and mononucleotide phosphotriester synthesis. / The trichloroethyl group was better than tribromoethyl, p-nitrophenethyl or methyl protecting groups for solution-phase synthesis. Trichloroethyl dichlorophosphite was used in block condensations to prepare CCCGA and UCAUAA. / An automated RNA synthesizer was developed. Nucleoside methyl chlorophosphites were used with silica gel supports. Polystyrene, polyacryloylmorpholide and controlled pore glass supports were also used but were not as satisfactory. Oligoribonucleotides, up to 17 units long, were rapidly prepared in high overall yield. The sequences were purified by TLC and gel electrophoresis. Enzymatic degradations and HPLC confirmed the composition of the products.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 173-179). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references (leaves 173-179). Also available on the Internet.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 263-272). Also available on the Internet.

Thesis (Ph.D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 263-272). Also available on the Internet.

The concept of combining two well established areas of organic chemistry, viz., organosilicon chemistry and the use of chiral auxiliaries, into a viable, alternative method of asymmetric synthesis has only very recently begun to receive attention. At the outset of this investigation, no asymmetric reactions of silyl enol ethers, chiral by virtue of optically active substituents on the silicon, had been reported. A range of novel chiral silyl enol ethers have thus been prepared from a variety of ketones, including pinacolone, cyclohexanone, and α-tetralone, and employing menthol, borneol, and cholesterol as chiral auxiliaries. These preparations have been achieved via several distinct routes, including a novel convergent approach involving the isolation of either the chloro(menthyloxy)dimethylsilane or the (bornyloxy)chlorodimethylsilane. The MS and NMR spectra of these silyl enol ethers were examined in detail and, in the case of the crystalline cholesteryloxy silyl enol ether, the X-ray structure has been determined. The potential of chloroalkoxysilanes to act as general, chiral derivatizing agents has been established by the preparation of diastereomeric silyl acetal mixtures of racemic secondary alcohols (e.g. I-phenylethanol and 2-octanol). The experimental diastereomeric ratios, obtained by GLC and ¹H NMR spectroscopy, approached the expected value of unity, confirming the potential of the alkoxychlorosilanes as chiral probes. The chiral silyl enol ethers have been successfully oxidized to the corresponding α-siloxy ketones employing MCPBA, MMPP, and 2-(phenylsulphonyl)-3-phenyloxaziridine as oxidizing agents and the diastereomeric excesses obtained, which varied from 0 to 16%, indicated some potential for stereochemical control. Alkylation and hydroxyalkylation reactions of the silyl enol ethers have yielded the expected α-iert-butyl and β-hydroxy ketones in good to excellent material yields, with the enantiomeric excesses, as determined by chiral shift reagent studies, reaching 14%. To improve the stereo control in these reactions, attempts have been made to prepare chiral silyl enol ethers with auxiliaries possessing the potential for transition state complex co-ordination in the reactions under consideration. The preparation of such silyl enol ethers, incorporating the proline-derived auxiliaries, N-methyl-2-hydroxymethylpyrrolidine and 2-methoxymethylpyrrolidine met with only limited success. In an alternative approach, three derivatives of 2,3-dihydroxybornane have been prepared. However, two of these auxiliaries, viz., 3-exo-benzyloxy-2-exo-hydroxybornane and 3-exo-(1-methoxyethoxy)-2-exo-hydroxybornane failed to form silyl enol ethers, even under considerably more vigorous conditions than normally employed. The third derivative, 3,3-ethylenedioxy-2-hydroxybornane has been successfully utilized in the preparation of a pinacolone-derived chiral silyl enol ether. Hydroxyalkylation of this compound with benzaldehyde has yielded the β-hydroxyketone with significantly improved enantiomeric excess (26%) and a transition state complex has been proposed to rationalize this improvement.

Sasol endeavors to expand its current business through the beneficiation of commodity feedstreams having marginal value into high-value chemicals via cost-effective processes. In this regard Merisol, a division of Sasol has access to phenolic and cresylic feedstreams, which have the potential to be converted to fine chemicals. Targeted products include para-anisaldehyde, ortho- and para-hydroxybenzaldehyde which are important intermediates for the manufacture of chemicals used in the flavor and fragrance market and various other chemicals. The use of CO technology (HF/BF3) to produce these aldehydes in a two-step process from phenol as reagent is economically attractive due to the relative low cost and other benefits associated with syngas as reagent. The aim of the study was to evaluate and understand this relatively unexplored approach to the formylation of aromatic compounds. The reactivity of both phenol and anisole proved to be much lower than that of toluene. The main aldehyde isomer (para) produced in these HF/BF3/CO formylations as well as of other ortho-para directing mono-substituted benzenes tested in our laboratories were in accordance with published results. Efforts to increase substrate conversion resulted in substantial secondary product formation and mechanistic investigations showed this to be a consequence of the inherent high acidity of the reaction environment. The effect of different substituents on the relative formylation rates of benzene derivatives was investigated. These results showed that methyl groups are activating while halogens are deactivating relative to benzene as substrate. The decrease in reactivity from fluorobenzene> chlorobenzene> bromobenzene is in accordance with formylation trends observed in other acidic systems. Deuterium labeling experiments were applied to gain additional information on the formylation reaction mechanism. This study provided interesting but inconclusive results in support of the so-called intra-complex mechanism. All reported studies as well as our own work suggested that HF and BF3 in (at least) stoichiometric amounts are required for effective formylation with CO. Under these conditions this methodology for effecting aromatic formylation is not economically viable. Industrial application of formylation using CO will require the development of new catalysts or methodology to allow the use of HF/BF3 in a catalytic way. In this regard ionic liquids as a new and ecological-friendly field was explored. Chloro-aluminate ionic liquids promote the carbonylation of alkylated aromatic compounds, but fails in the case of oxygenated aromatics. Aldehyde yields of formylation in the acidified neutral ionic liquids were generally similar compared to reactions conducted in HF as solvent/catalyst. Formylation of anisole and toluene, but not of phenol in the neutral ionic liquids resulted in increased secondary product formation in comparison with hydrogen fluoride used as solvent/catalyst. This difference in behavior is not understood at present, but suggests that phenol is a good substrate for formylation in this medium, particularly with the development of a system catalytic with respect to HF/BF3 in mind. / Prof. C.W. Holzapfel