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.

A series of 88 novel tetrahydroisoquinoline (TIQ) compounds have been synthesised for applications in asymmetric catalysis. Several chiral TIQ ligands, possessing N,O and N,N donor atoms, have been prepared and evaluated for the catalytic asymmetric transfer hydrogenation (ATH) of pro-chiral ketones. The highest selectivity obtained for the asymmetric transfer hydrogenation of acetophenone with the N,O donor atom ligands was >99 % ee at low temperatures in iso-propanol with [Ru(p-cymene)Cl2]2 as a pre-catalyst. The observed enantioselectivity was supported by theoretical calculations using the Jaguar interphase program (Paper I). An enantioselectivity of 70 % was obtained with the ligands possessing the N,N donor atoms with the observation that water played a significant role in the enantioselectivity of the ATH reaction of acetophenone (Paper II). An investigation into the usefulness of the TIQ scaffold with other donor atoms was also undertaken. A series of novel P,N oxazoline ligands were synthesised and coordinated to Iridium BArF. These complexes were screened as chiral catalysts for the high pressure asymmetric hydrogenation of unsymmetrical olefins. The reactions proceeded readily at ambient temperature and provided selectivities of up to >91 % ee with excellent conversion rates (>99 %) for the benchmark reactions. Based upon these favorable results, the ligands providing the best results were further screened on a variety of functionalized and unfunctionalised olefins (Paper III). The success of the TIQ backbone in ATH reactions prompted an investigation into its applications in carbon-carbon (C-C) bond forming reactions. The Henry (nitroaldol) reaction is an important C-C bond forming reaction with the chiral oxazoline class of ligands being widely utilised. A series of novel, chiral TIQ oxazoline ligands were synthesised and complexed to various metals (Cu, Sc, Co, Zn, Ni and Mn). These complexes were screened as chiral catalysts in the asymmetric Henry reaction. The highest enantioselectivity (>77 %) was obtained when Cu(OAc)2was employed as a pre-catalyst and iso-propanol as a solvent (Paper IV). The final chapter deals with carbon-sulphur bond formations facilitated by the conjugate addition of thioglycolate to various chalcones. A series of novel, chiral TIQ N-oxide ligands were synthesised and complexed to lanthanum. The complexes were screened for activity against the benchmark reaction and an enantioselectivity of 81 % was obtained. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2010.

This study has shown that alkythioboranes 1,3,2-dithiaborolane and 1,3,2-dithiaborinane, disproportionated significantly during their synthesis. Their interaction with 1-octene has been investigated, and the rate constants, enthalpies and entropies of the hydroboration process, have been determined. The thermodynamic and kinetic parameters obtained have shown that the hydroboration reaction is sluggish and proceeded via an associative mechanism. / Thesis (Ph.D.) - University of KwaZulu-Natal, Pietermaritzburg, 2008.

The present work represents an attempt to study the inhibition of corrosion of mild steel in acid media by seventeen furan derivatives, at 17 to 30 different inhibitor concentrations, from 0 up to 20 mMole per liter. / One of the techniques used to correlate the inhibitive action of organic compounds is based on the Linear Free Energy Relationship (LFER). The relationship is used to elucidate the mechanism of inhibition, by studying the effects of physico-chemical characteristics of the inhibitor molecules, such as functional group, polar function electron density, steric effects, and (pi)-orbital character of the donating electrons on the corrosion inhibition of mild steel in acid solution. / The results show that furfuryl alcohol, 2,5-furan dimethanol, and 2-furonitrile act as excellent inhibitors over the entire concentration range covered in this study, whereas the remaining investigated compounds exhibit substantial fluctuations in the inhibitive action with concentration. Frequent maxima and minima of inhibitive action have been observed. This behaviour can be explained on the basis of the different reaction mechanisms of the absorbed intermediate inhibitor complex at the metal surface. / The results of the study suggest that the inhibitive action of ortho-substituted compounds is influenced by steric effect. Although LFER is a valuable tool for comparing inhibitive actions of various compounds, other criteria should be considered. These criterion or special effects include polymerization, (pi)-orbital electrondelocalization, and mesomeric effects. Such effects could cause a compound to act as a good inhibitor, irrespective of considerations relating to electron affinity.

The novel candidate high energy insensitive explosive; 2,5-diamino-3,6-dinitropyrazine (ANPZ-i) has been prepared in acceptable overall yield. ANPZ-i was synthesised by the nitration of 2,5-diethoxypyrazine using nitronium tetrafluoroborate (NO2+BF4-) in sulfolane and the subsequent amination of 2,5-diethoxy-3,6-dinitropyrazine, under autoclave conditions. Oxidation studies towards the dioxide derivative of ANPZ-i, 2,5-diamino-3,6-dinitropyrazine-1,4-dioxide (PZDO), were unsuccessful. The synthesis of existing high explosives; 2,6-diamino-3,5-dintropyrazine (ANPZ) and 2,6-diamino-3,5-dinitropyrazine-1-oxide (PZO) has been scaled up to produce approximately 25 g batches of material. A number of novel nitrations using NO2+BF4- have been carried out on a range of chloro-, methyl- and hydroxy-functionalised quinoxalines and quinazolines. A range of novel functionalisations have also been carried out on the platform molecule; 2,4-diamino-6,8-dinitroquinazoline giving rise to 2,4-diamino-6,8-dinitroquinazoline-1,3-dioxide (di-N-oxidation product), 2,4,7-triamino-6,8-dinitroquinazoline (monoamination product) and 2,4,6,8-tetra-aminoquinazoline (dihydrogenation product). Detonics molecular modelling was carried out on the following target molecules: 2,5-diamino-3,6-dinitropyrazine-1,4-dioxide (PZDO), 2,5,8-triamino-3,6,7-trinitroquinoxaline-1-oxide and 2,5,7-triamino-4,6,8-trinitroquinazoline-1-oxide. The detonation velocity of the new explosive molecule; 2,5-diamino-3,6-dinitropyrazine (ANPZ-i) was calculated and it was found to be a similar value to that obtained experimentally for the existing high explosive RDX. Calculation by molecular modelling of the steric energies of ANPZ, PZO, ANPZ-i and PZDO gave a quantitative assessment of the difficulty in oxidising ANPZ-i to give PZDO. Extensive analysis of carbon-13 NMR spectroscopy shift values was carried out for approximately twenty nitrogen heterocyclic compounds. Comparison of shift values indicated consistency in the interpretations. On-line literature searches have shown that the following compounds prepared in this project are new: 2,3,6-trichloro-5-nitroquinoxaline, 2,3-dimethoxy-6,7-dinitroquinoxaline, 2,3,6-trichloroquinoxaline-1-oxide, 2,4-diamino-6,8-dinitroquinazoline-1,3-dioxide, 2,4,7-triamino-6,8-dinitroquinazoline and 2,5-diamino-3,6-dinitropyrazine (ANPZ-i). Furthermore, new synthetic routes have been used in the preparation of the following compounds: 2,3-dichloro-5-nitroquinoxaline, 2,3,6,7-tetrachloro-5-nitroquinoxaline, 2-hydroxy-6-nitroquinoxaline, 2-hydroxy-3-methyl-6-nitroquinoxaline and 2,5-diethoxy-3,6-dinitropyrazine.

A range of N-H alkynylaziridines were prepared from amphoteric unprotected aziridine aldehydes without protecting-group manipulation. Unprotected alpha -amino allenes can be obtained from these strained propargyl amines via a 9-BBN mediated hydride transfer. Further transformation of alpha -amino allenes to 2,4,6-trisubstituted pyridines was realized. We also developed another class of amphoteric molecules – alpha-boryl aldehydes, equipped with the tetrahedral MIDA boryl group. A wide range of boryl-substituted building blocks or functionalized boronic acid derivatives have been accessed from these bench-stable alpha-borylcarbonyl compounds. Further chemoselective transformations of these alpha-boryl aldehyde derived building blocks have been conducted, where alph-boryl isocyanates, alpha-aminoboronic acids, acylboronates, and borylated heterocycles were achieved through the decarboxylative functionalization of alpha-borylcarboxylic acids.

The primary aim of this project was to synthesize new heterocyclic dimers of isoflavones and flavones, and investigate various methodologies for their synthesis. The secondary aim of the project was to synthesize some flavonoid natural products. Dimeric systems were synthesized using various methodologies including acid catalyzed arylation of isoflavanols and flavanols, acid catalyzed dimerization of flavenes, oxidative dimerization, Sonogashira coupling, Ullmann coupling and Suzuki-Miyaura coupling reactions. The acid catalyzed arylation of isoflavanols was found to proceed in a very stereoselective fashion to give trans-4-arylisoflavans in good yield in a single step. However, related flavanols under similar conditions gave mixtures of cis and trans isomers of 4-arylflavans. Interestingly, it was found that appropriately substituted flavenes, upon treatment with acid undergo stereoselective rearrangement and dimerization to give benzopyranobenzopyrans in high yields. A rationale for the rearrangement is proposed and this dimerization was used for the stereoselective synthesis of the natural product dependensin. As part of the project, some polycyclic natural products such as octandrenolone, flemiculosin, 3-deoxy-MS-II and laxichalcone were also synthesized. Oxidative dimerization of activated isoflavones was found to be very regioselective, and novel isoflavone dimeric systems were synthesized. Related flavones however, failed to undergo dimerization under similar conditions. A probable explanation for high regioselectivity in the case of isoflavones and unreactivity of flavones has been presented. Phenol oxidative coupling was used for the one-step synthesis of another natural product kudzuisoflavone-A from daidzein. Sonogashira coupling was utilized for the synthesis of dimeric systems linked via an acetylic linker. A variety of soflavone isoflavone, flavone-flavone and isoflavone-flavone dimers were synthesized in "one-pot" by this methodology and in excellent yields. Although Ullmann coupling was found not to be suitable for the synthesis of isoflavone or flavone dimers, one-pot Suzuki-Miyaura methodology gave flavone dimers and various other heterocyclic dimers in good yields.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2005. / Härtill 4 uppsatser.

Thesis (Ph.D.) -- University of Adelaide, Department of Organic Chemistry, 1981.

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.