Thesis (M.S.)--University of Nevada, Reno, 2008. / "August, 2008." Includes bibliographical references (leaves 45-54). Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2008]. 1 microfilm reel ; 35 mm. Online version available on the World Wide Web.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

The problem initially presented was the structural elucidation of a compound obtained when 2,5-dimethylpyrrole was subjected to conditions of acidic reduction. Previous workers had assigned a molecular formula C₁₂H₁₇N to this product and a partial structure had been put forward based on the indolenine system. In the course of this work it was found that the compound obtained by these earlier workers was the result of a reductive self-condensation of 2,5-dimethylpyrrole, and Its structure was conclusively established as 1,3,4,7-tetramethylisoindoline. The methods used in the structural elucidation of this product included elemental analysis of its derivatives, measurement of its basicity and equivalent weight, infrared and ultraviolet spectroscopic evidence, oxidative degradation, and its proton magnetic resonance spectrum. Two related isoindolines were prepared by different routes. 2,4,7-trimethylisoindoline was synthesised by methods analogous to those already known, and the ultraviolet spectrum of its methiodide, when compared with that of the methiodide from 1,3,4,7-tetramethylisoindoline, reinforced the structural assignment of the latter. 1,3-diphenyl-4,7-dimethylisoindoline was obtained by the reductive condensation of acetonylacetone with 2,5-diphenylpyrrole (which did not undergo self-condensation). The favourable result of this reaction suggested that a similar condensation may have occurred to give the 1,3,4,7-tetramethylisoindoline and also admitted the possibility of a general synthesis of substituted isoindolines by this route. An attempt was made to resolve the mechanism of the 2,5-dimethylpyrrole condensation, for which either a Diels-Alder reaction or a ring-opening process may be postulated. The failure of the dimethylpyrrole to show dienic character, even in the presence of very strong dienophiles, together with positive evidence for ring-opening and ketone-pyrrole condensation argued forcibly for the latter mechanism. / Science, Faculty of / Chemistry, Department of / Graduate

Reproduction de : Thèse de docteur-ingénieur : Chimie : Metz : 1977. / Titre provenant de l'écran-titre. Notes bibliogr.

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Described in this thesis is the development of a key Diels-Alder reaction for use in a total synthesis of the potently immunosuppressant marine alkaloid palau'amine. This study focuses on the originally proposed structure of palau'amine. The strategy utilizes a computationally designed thiohydantoin dienophile as the 2pi component and a thermally stable 2-silyloxy-5-(silyloxymethyl)cyclopentadiene as the 4pi component in the critical Diels-Alder reaction. Essential to the design and study of these partners was the use of computational density functional theory (DFT) predictions. / Four families of dienophiles---oxazolones, dehydroalanines, hydantoins and thiohydantoins---were investigated. The hydantoins and thiohydantoins react with cyclopentadiene with up to 13:1 exo-selectivity while the dehydroalanines are modestly selective and the oxazolones are unselective. The exo-selectivity of the hydantoin and thiohydantoin dienophiles is attributed to a novel stabilizing interaction whereby the lone pair of electrons on nitrogen interacts with a developing positive charge on the diene in the transition state. In terms of reactivity, the oxazolones are the superior dienophiles. The reactivity of the thiohydantoins is greater than that of analogous hydantoins and approaches that of the oxazolones. The bolstered reactivity of the thiohydantoins is attributed to the increased donation of the nitrogen lone-pair into the thiocarbonyl bond. This phenomenon was recognized first in DFT predictions and then proven experimentally. Synthetic access to the requisite beta-(chloromethylene)thiohydantoins necessitated the development of a reaction between dilithium diamides and thiophosgene. / 2-silyloxy-5-(silyloxymethyl)cyclopentadienes were studied experimentally and computationally and found to be much more stable than conventional 5-substituted cyclopentadienes towards thermal decomposition by 1,5 hydride shift. The new dienes undergo Diels-Alder reaction with oxazolone and thiohydantoin dienophiles with exoselectivities as high as 6:1 for nonchlorinated dienophiles. Fully functionalized chlorinated exo-cycloadducts were prepared with up to 1.5:1 selectivity and subjected to oxidative ring-opening to reveal the persubstituted core of palau'amine.

The aim of this project was a broad one, namely to develop general methods for the preparation of nitrogen-containing heterocycles. This topic also encompasses the preparation of precursors to heterocycles with the goal of obtaining compounds that can undergo various transformations to give different cyclic products (general synthetic precursors). Workers in our group have previously reported the preparation of indolizinones from N-propargyl enaminones. Immediate goals were to elucidate the mechanism of this transformation, optimise its yields and explore its generality. Initial work revealed a possible reaction intermediate in the form of isomeric N-allenyl enaminones. These compounds can be easily prepared from N-propargyl enaminones using potassium tertbutoxide. Although parallels between the two reactions were noted, the presence of N-allenyls as reaction intermediates was not substantiated. In spite of this, N-allenyl enaminones were considered to be potentially valuable compounds in their own right and their chemistry was briefly explored. It was shown that they undergo hydroboration smoothly yielding only one hydroboration product. This was observed using dynamic iiB NMR spectroscopy. Subsequent oxidation gave interesting results and these are discussed further. At this stage it was considered important to prepare piperidine and acyclic analogues of the N-allenyl enaminones already synthesised. Both preparations proved problematic and were ultimately abandoned. Although these attempts were not fruitful, a number of interesting observations were made en route and contribute to the discussion. Whilst attempting to prepare acyclic analogues it was found that when a mixture of a secondary enaminone and propargyl bromide was treated with silver nitrate functionalised pyrroles were formed. This method of pyrrole formation, although low yielding (~25%), was both novel and intriguing. As pyrroles are important heterocycles and common synthetic targets, further work was carried out to elucidate the mechanism in operation during this conversion. A thorough investigation led to a proposed mechanism involving silver-mediated hydro amination followed by an intramolecular nucleophilic substitution. This proposed mechanism is discussed further. Carrying out the reaction over two steps was found to improve the procedure. Carbon-carbon bond formation prior to an intramolecular silver-catalysed hydroamination provides superior overall yields. Intramolecular hydroamination can be carried out at room temperature or using microwave irradiation. Employing microwave irradiation reduces reaction times from sixteen hours to sixty seconds without any decrease in yields. This process was extended to bicyclic systems, namely N-bridgehead pyrroles. The preparation of the necessary cyclic precursors via a protection-deprotection strategy is described. N-Bridgehead pyrroles provide the framework for pyrrolizidine, indolizidine and lehmizidine alkaloids and general synthetic protocols toward the synthesis of such alkaloids is proposed. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.

No description available.

Diss. (sammanfattning) Stockholm : Karol. inst., 2004. / Härtill 4 uppsatser.

Thesis (Ph.D.)--University of Western Sydney, Nepean, 1994. / Bibliography: leaves 227-256.