Thesis (Ph. D.), Memorial University of Newfoundland, 1998. / Bibliography: leaves 142-156.

A full IH, l3C and 31P NMR assignments of phosphoric triamides 1-oxo-2,8-diphenyl-2,5,8-triaza-l-phosphabicyclo [3.3.0]octane (1), l-oxo-lO-phenyl-4,7,lO-triaza-2.3-benzo-l-phoshabicyclo [5.3.0]decane (2) and 1-oxo-4,7,lO-triaza-2,3,11,12-dibenzo-l-phosphabicyclo[5.5.0]dodecane (3) which have been recently synthesised was accomplished. The solution state NMR analysis of these compounds showed a number of interesting spin systems upon moving from 1→2→3, spanning from ABC to ABCDX spin systems where X is phosphorus nucleus. The three systems showed a high degree of rigidity in solution state, which made it possible to compare dihedral/torsion angles determined from solution state NMR with those of X-ray diffraction data. Both X-ray diffraction and NMR analysis supported the molecular conformations. A significant solvent effect was observed for solutions of compounds 1, 2 and 3 in benzene-d6 compared to solutions in chloroform-d1 and acetone. Benzene-d6 showed a generally upfield chemical shift of methylene protons in particular, and this is assumed to be due to different solvent-substrate interactions and to the magnetic anisotropic effect of the solvent. / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

MSc (Chemistry) / Department of Chemistry / Quinolines are well known naturally occurring heterocyclic compounds with nitrogen as a heteroatom. Quinolines are also one of the major classes of naturally occurring compounds and the interest in their chemistry is due to the wide range of their biological activities. The objective of the project was the synthesis of novel tetra-substituted quinoline-3carboxamides and subsequent transformation to other novel derivatives and evaluation of their biological activities against malaria and cytotoxicity. In achieving the objective, 2-chloroquinoline-3-carbaldehyde analogues 54A-G were synthesised from the reaction of acetanilides 53A-G and acetic acid. Knoevenagal reaction of 2chloroquinoline-3-carbaldehydes 54A-G with thiazolidinedi-2,4-one 62 provided 2chloroquinoline-3-methylene thiazolidinedi-2,4-one 55A-G which then underwent nucleophilic substitution reaction with sodium azide and afforded (Z)-5-((tetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56A-F. (Z)-ethyl-2-(2-5-((7bromotetrazolo [1,5a] quinolin-4-yl) methylene-2,4-dioxothiazolidin-3-yl) acetamido) acetate 57 was synthesised from the reaction of (Z)-5-((7-bromotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56D and ethyl-2-(2-chloroacetamido) acetate 65. The structures of the compounds were characterised by 1D NMR (1H, 13C, and DEPT 135), IR spectroscopy, elemental analysis and high-resolution mass spectroscopy. Novel selected synthesised quinoline compounds were evaluated of in vitro for two biological assays; namely anti-malarial activity and cytotoxicity. The anti-malaria activities of the novel quinoline compounds against 3D7 strain of the malaria parasite Plasmodium falciparum displayed that 2,6-dichloroquinoline-3-methylene thiazolidinedi-2,4-one 55C, (Z)-5-((7-fluorotetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56B and (Z)-5((7-ethoxytetrazolo [1,5a] quinoline-4-yl) methylene) thiazolidinedi-2,4-one 56F are potential malaria drugs since they reduced the percentage parasite viability to 25.80, 12.40 and 20.40 respectively. These results were further substantiated by their IC50 values 0.40, 0.04 and 0.50 µg/mL. Compound 56B displayed the highest cytotoxicity activity against human cervix adenocarcinoma cells displaying percentage viability of 14.22 %. Compounds 56F and 56C displayed moderate cytotoxicity activity at 56.60 and 59.81 % viability. / NRF

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy

Imidazo[1,5-a]pyridines are an important and versatile class of N-heterocyclic compounds due to their stability, unique biological, and photochemical properties. Due to the conjugation and charged structure, their properties are extended to conducting electricity and also have electronic properties. They can be used for chelating transition metals especially heavy metals that can be harmful to living things (including human). The aim of this research was to develop more useful imidazo[1,5-a]pyridines which are stable in both free and complexed state. A variety of imidazo[1,5-a]pyridyl compounds was synthesized following three useful methods namely (i) The first route includes the isolation of imine intermediates which were then treated with phosphorus oxychloride in one case and hydrochloric acid in another case as catalysts. Both cases resulted in the yield of the same imidazo[1,5-a]pyridyl compounds. (ii) The second route was the development on the first route for those imine intermediates that could not be isolated and only hydrochloric acid catalyst was used. In both the first and second routes, paraformaldehyde was used for the ringclosure step of the reaction. The last route for the formation of imidazo[1,5-a]pyridyl compounds did not involve the use of the paraformaldehyde reagent. The suitable routes were followed depending on the nature of the targeted products and the reaction yields were moderate to excellent. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg,2010.

The halogenated derivatives of heterocyclic compounds (haloarenes) are highly utilized in many fields of chemistry, including drug discovery, medicinal, and material chemistry. There are a variety of ways to functionalize an aromatic system and introduce halogen substituent into the ring. However, electrophilic aromatic substitution (EAS) has been the focus of growing attention, particularly for electronrich substrates. Electrophilic aromatic bromination protocols are one of the most important electrophilic aromatic substitution reactions. However, preparation of bromoarenes classically recommends the use of highly oxidative agents along with utilizing various metal catalysts in a halogenated solvent. The corrosive and toxic nature of these reagents and need of harsh conditions for these protocols make their utility less desirable in current practice. Furthermore, lack of regioselectivity for most substituted aromatics is the other distinguished drawback, since most products contain ortho/para directors which afford a mixture of isomers. The innovation of our procedure for the bromination of various substituted aromatic compounds is twofold in that highly regiospecific para-bromination of activated aryls by treatment with NBS has been accomplished. Although various reaction mediums, such as cyclohexane, acetone, and acetonitrile has been used in this procedure, the significant high yields of the product formation along with the very short reaction times using acetonitrile make this approach more attractive. That this regiospecific p-substitution takes place under such mild conditions leads us to question whether it is EAS.

Hak-fun Chow. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1981. / Bibliography: leaves 70-73.

N-Heterocyclic carbenes (NHCs) are an important class of compounds responsible for a wide variety of chemical transformations. NHCs may be used as organocatalysts that permit non-traditional carbon carbon bond formations due to their renowned ability to invert the electrophilic character of aldehyde carbonyl groups, a concept otherwise known as polarity reversal or umpolung reactivity. Despite their ubiquity with respect to accessing the umpolung of aldehydes, fundamental studies of these reactive species are still rather limited and narrow in scope. As a result, clarifying and solving problems relevant to umpolung-themed asymmetric catalysis becomes quite challenging. In this regard, our work has been focused on a three-pronged approach towards providing a more unified understanding of these complex catalytic systems. First, we describe the synthesis of unprecedented carboxylate-tethered triazolium NHCs and use them in the intramolecular Stetter reaction to understand their function. Second, we describe the acidities of a broad range of both chiral and achiral NHCs that have never had their acidities assessed before and use them to construct the first linear free-energy relationships of their kind. Finally, we develop a simple and noninvasive experimental protocol in which we can quickly benchmark the performance of a series of chiral catalysts by way of single competition experiments. We anticipate that these studies will have direct implications on the development of novel NHC-catalyzed reactions.

2-Pyridinyl-2-pyrazinylmethanone (L4) is able to exist in the neat ketone form and gem-diol form (2-C5H4N)C(OH) 2(2-C4H3N2) (L4a) in its Ag(I) and Cu(II) complexes. Two isostructural Cu(II) complexes [Cu(L4 a)2X2·2H2O, X = C lO4-, BF4-] with the L4a ligand taking the chelating mode are formed, in which the different linkage modes of lattice water molecules between the Cu(L4 a)22+ units lead to different space groups in crystallization. Through versatile anion-pi(pyrazinyl ring) and hydrogen-bonding interactions, the Cu(L4a)22+ units are assembled into distinct 3-D metal-organic hybrid frameworks in these two complexes. Different ligation modes of L4 in its neat ketone and gem-diol forms are found in its silver(I) complexes that exhibit diverse network structures. / By tuning the counter anion, mu2-bridging 2,6-pyridinediylbis(4-pyridinyl)methanone (L2) via two terminal 4-pyridyl N atoms links Ag(I) ions into two distinct structural motifs in its silver(I) complexes, namely infinite helical chain and metallacyclophane, which are further assembled into higher-dimensional metal-organic frameworks through Ag···Ag, pi···pi, hydrogen-bonding, Ag···O=C, carbonyl···carbonyl, as well as unconventional anion-pi(pyridyl ring) interactions. Intermolecular dipolar carbonyl···carbonyl interaction of three principal types serves as a common dominant non-covalent interaction in the supramolecular conglomeration of these complexes. / Di-2-pyrazinylmethanone (L3) readily undergoes metal-assisted hydration reaction in its Ag(I), Cu(II), Co(II) and Cd(II) complexes, and is potentially useful for the construction of extended coordination networks with its gem-diol (2-C4H3N2)2C(OH) 2 (L3a) or anionic (2-C4H3N 2)2C(OH)CO- (L3b) form as an architectural moiety. A sheet-like net, an alpha-polonium topology of the NaCl-type and a rare 1-D nanotubular coordination architecture has been generated in its Ag(I) complexes through the tuning of counter-anions. Three isostructural complexes Cu(L3a)2X2· nH2O (n = 4.5; X = ClO 4-, BF4-, PF 6-) have been obtained and characterized. The 3-D host frameworks of these complexes are constructed from the linkage of mononuclear Cu(L3a)22+ metallotectons through a combination of hydrogen-bonding and anion-pi interactions, leading to honeycomb-like channels that accommodate guest water molecules. A cubane-like Co(II) cluster stabilized by L3b and the topological structure of Cd(II) complexes with L3a have also been obtained. / Di-2-pyridinylmethanone (di-2-pyridyl ketone) is a well-known versatile ligand among the basic building blocks for the construction of metal-organic hybrid materials. It can exist in its neat form, or in the hydrated gem-diol and alcoholated hemiketal forms. In this thesis, through modification of the heterocyclic ring and the bridging functional group, we have systematically synthesized a series of transition metal complexes of five carbonyl-bridged heterocycles (L1-L5) (see P. xi) and two structural analogs with sulfinyl and sulfonyl bridging groups (L6-L7), which are expected to provide flexible coordination bonding and additional non-covalent interactions in the generation of metal-organic hybrid frameworks. / In the two mononuclear Cu(II) complexes of 2,6-pyridinediylbis(3-pyridinyl)methanone (L1) with the ligand taking a chelating mode, four distinct types of unconventional intermolecular C=O···pi interactions between the carbonyl and pyridyl rings were identified. Moreover, the mu2-bridging L1 via two 3-pyridyl N atoms proves to be an excellent building block for the construction of disilver(I) metallacyclophanes with a [Ag2(L1) 2]2+ skeleton in a series silver(I) complexes. The [Ag 2(L1)2]2+ metallacycle functions as a secondary building unit to form infinite chains through Ag···O=C or argentophilic interactions, which are further assembled into a 3-D supramolecular structure via collective weak interactions including the anion-pi interaction. The employment of different Cd(II) and Hg(II) salts to react with the flexible L1 ligand has resulted in infinite chain, mononuclear, and 3-D network structures, in which L1 takes eta1-terminal, N,N-chelating, and mu2- and mu3-bridging modes. In these complexes, C--H···O, C--H···Cl--M hydrogen bonding, pi···pi, carbonyl···carbonyl, O(perchlorate)···C=O, as well as unconventional anion···pi(pyridyl ring) interactions, play important roles in consolidation of the supramolecular frameworks. / Sulfinyldipyrazine (L7) is capable of forming intriguing architectures in various sivler(I) salts, including a series of coordination polymers exhibiting (4,4) net, infinite chain and 3-D framework structures. A remarkable characteristic of L7 is that the electron-deficient pyrazinyl ring and the sulfonyl group provide potential bonding sites for lone-pair-aromatic interactions in the supramolecular assemblies, such as anion-pi and S=O···pi(pyrazinyl ring) interactions. The S=O moiety of the sulfonyl group exhibits an affinity for the pyrazinyl ring, which is evidenced by the existence of two types of such interaction in the silver(I) complexes of L7. (Abstract shortened by UMI.) / by Wan, Chongqing. / Adviser: Thomas C. W. Mak. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3504. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 172-190). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307.