<p> Carbocyclic and heterocyclic compounds are ubiquitous in nature. Therefore, the discovery and development of new ring forming reactions are of paramount interest to synthetic organic chemists. Recently, the intramolecular cyclization of reactive intermediates, such as anions, cations, and radicals have provided a number of new methods by which known and novel ring systems can be constructed. Cyclizations involving tandem, or multiple sequences have gained considerable popularity due to their high overall efficiency and remarkable speed by which these processes can yield complex polycyclic ring systems.</p> <p> Carbenes are another interesting class of reactive intermediates which undergo characteristic reactions. The cyclization reactions of carbenes have not been studied to a significant extent. In particular, the work described in this thesis outlines the only study of the intramolecular cyclization of dioxycarbenes onto a tethered alkyne moiety.</p> <p> The first section of this dissertation details the development of a convenient new class of thermal dioxycarbene precursors, dioxyoxadiazolines I, which display many significant advantages over previously used sources of dioxycarbenes ll. (See Diagram in Thesis)</p> <p> The second section of this dissertation details the use of dioxyoxadiazolines possessing a tethered triple bond for the thermal generation of dioxycarbenes III which are capable of intramolecular cyclization. It was found that the cyclization of a dioxycarbene onto a tethered triple bond results in the regioselective generation, of another reactive intermediate, a 3,3-dioxyvinylcarbene (IV or V, depending on the nature of R'), which can undergo a number of interesting intermolecular reactions. This approach leads to the rapid construction of some interesting and rather complex polycyclic heterocyles which are, in many cases, obtained with high regioselectivity and sometimes even high stereoselectivity. (See Diagram in Thesis)</p> <p> The results described in this thesis mark the discovery and development of a new synthetic methodology which may, by appropriate choice of the starting material, provide a valuable tool for the rapid and selective synthesis of a number of heterocyclic ring systems.</p> / Thesis / Doctor of Philosophy (PhD)

<p> Aryl radical ring closures onto the azo functional group were investigated. A series of ortho-substituted aryl radicals (83a-f) have been generated by bromine abstraction from the corresponding 1-(orthobromophenyl)-1-methoxy-azoethanes (82a-f) by tributyltin radicals. The radicals generated underwent cyclization in the 5-endo sense, to ultimately afford the substituted indazoles (86a-f). There was also some evidence for cyclization to the other azo nitrogen (closure in the 4-exo sense) to form a 4-membered ring. The aryl radical also underwent hydrogen atom abstraction from tributyltin hydride in competition with cyclization. Since the rate constant for hydrogen atom abstraction from tributyltin hydride by aryl radicals is known, this makes it possible to estimate the rate constants for cyclization throughout the series.</p> / Thesis / Master of Science (MSc)

No description available.

Submitted in fulfillment of the requirements of the Degree of Doctor of Technology: Chemistry,Durban University of Technology, 2014. / Aromatic heterocycles are highly important structural units found in a large number of biologically active natural compounds, pharmaceuticals and catalytic compounds. They have a crucial role in organic syntheses, which results in the generation of high value products. Among heterocycles, those containing nitrogen are the most indispensable structural motifs and are widely used against dreaded diseases such as Malaria, TB, HIV/AIDS and Cancer. The inclusion of highly electronegative atoms such as fluorine in these organic molecules render them very reactive towards proteins. Furthermore these molecules exhibit strong interactions with surfaces of quantum range particles of elemental gold. Various approaches for the synthesis of novel gold nanoparticles linked to potent bioactive molecules are documented and their application as drug delivery systems are of immense value to human health. Also many chemical and physical methods are available for the synthesis of gold, silver and palladium nanoparticles however these methods are usually laborious and produce toxic by-products. The green approach is to use plant extracts to synthesise various size and shape nanoparticles which could be used in biological and catalytic systems. A simple one-pot two component and three component reaction using formyl quinoline, 2-aminothiophenol, thiosemicarbazone and trifluoromethylbenzaldehyde as a reactant to synthesise quinoline, pyridine and pyran based bioactive small molecules; these products are a quinoline type bearing a benzothiazole moiety, quinoline thio semicarbazone ligand, fluorine substituted dihydro pyridine, fluorine substituted dihydropyran and fluorine substituted pyridine derivatives. In total, fifteen compounds were synthesized eleven of which were novel; all compounds were characterized by spectroscopic techniques. In vitro anti-bacterial activities of the synthesized compounds were investigated against a representative panel of pathogenic strains. Compounds 6, 7, 8, 11 and 13 exhibited excellent anti-bacterial activity compared with first line drugs. Potent p53–MDM2 interaction inhibitors 2-thio-1,2-dihydroquinoline-3-carbaldehyde thiosemicarbazone and fluorine substituted new pyridine scaffold were successfully identified by structure-based design. An efficient one-pot four component route to the synthesis of trifluorinated pyrrolophenanthroline and fluoroquinoline pyrrolophenanthrolines was designed. In this reaction 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ionic liquid (DMTIL) was used as a reaction medium; no catalyst was required. The structure of the pyrrolophenanthrolines was deduced by IR and NMR analysis. These compounds were studied with Bovine Serum Albumin (BSA) through molecular docking. Hydrophopic, electrostatic and hydrogen bonding interaction played a crucial role in the binding to sub domain of BSA. Interaction studies of DMTIL with BSA by emission, absorption, synchronous fluorescence, circular dichroism (CD) and three dimensional emission (3D) spectroscopic techniques were under taken. The results from emission titration experiments revealed the existence of a strong interaction between BSA and DMTIL ionic liquid. It showed that compounds with lesser number of hydrogen bonds are found to be more active which is attributed to hydrophobic interaction and electrostatic interaction which also played a vital role in DMTIL binding to sub domain IB of BSA. A novel copper-loaded boron nitride nanosheet (Cu/BN) catalyst was prepared and fully characterized. It was used as an efficient and chemoselective catalysts for the synthesis of α-aminophosphonates by the Kabachnik-Fields reaction; twenty one α-aminophosphonates were synthesised. The enhanced catalytic activity and product yield was attributed to the increase of surface acidity. Overall, this methodology offered competitive advantages such as recyclability of the catalyst without further purification or without using additives or cofactors, low catalyst loading, broad substrate applicability and high yields. The application of this new nanocatalyst in organic synthesis will provide a novel pathway for the synthesis of pharmaceutically important compounds. Gold nanoparticle surfaces were modified with self-assembled monolayers of important thiol and disulfide bioactive molecules since considerable interest is due to their potential application as anti-cancer agents. Herein, a carbazole was conjugated to lipoic acid by using an amide coupling catalyst HBTU and DIEA reaction. The structure of the carbazole thio octanic acid (CTN) was identified by IR and NMR. CTN was attached to the gold nanoparticles surface and the capping behaviour was characterized by UV-vis spectroscopy, TEM, DLS and FTIR. The cytotoxicity of CTNAuNPs on A549 cell lines was determined using the MTT assay. The results suggest CTN and CTNAuNPs possess anti-proliferative properties in the cancerous A549 cells. Furthermore a dual thiol ligand was synthesized by using equimolar 4-aminothiophenol (4-ATP) and amino oxadiazole thiol (AXT). This dual ligand was attached to the gold nanoparticles surface (DTAu) and the capping behaviour was characterized by UV-vis spectroscopy, TEM, DLS and FTIR. The cytotoxicity of DTAu on A549 cell lines was determined using the MTT assay. The results suggest dual ligands (4-ATP, AXT) and DTAu possess anti-proliferative properties in the cancerous A549 cells. South African indigenous plants and agroforestry waste were also used in the synthesis of silver, gold and palladium nanoparticles (NPs). Green protocols such as the use of environmentally benign solvents and non-hazardous reagents were an added advantage to physical and chemical means. Furthermore these reactions were rapid and the size and shape of the NPs could be manipulated by choosing the correct medium. The formulation of natural medicinal compounds capped onto NPs was assessed for their anti-cancer activity, in A549 lung cancer line, and catalytic reduction of dyes and nitrobenzene derivatives were studied. These NPs displayed: Significant cytotoxicity to lung cancer cells with minimal effect on normal healthy cells. Outstanding catalytic reduction of pharmaceutical and textile waste effluents such as dyes and nitro aromatic compounds. In addition, palladium nanoparticles containing capped Moringa olifera compounds were used effectively in the Suzuki coupling reaction of iodobenzene and phenylboronic acid. The reaction was rapid and was conducted in an aqueous medium.

This thesis concerned about the Ru-catalyzed C-H functionalizations on the synthesis of 2-arylindole unit, silylation of heteroarenes and preparation of aryne precursor. In the first project, we developed the Ru-catalyzed C2-H arylation of N-(2-pyrimidyl) indoles and pyrroles with nucleophilic arylboronic acids under oxidative conditions. Wide variety of arylboronic acids afforded the desired product in excellent yield regardless of the substituents or functional group electronic nature. Electron-rich heteroarenes are well suited for this method than electron-poor heteroarenes. Halides such as bromide and iodide also survived, further derivatisation of the halide is shown by Heck alkenylation. In order to find catalytic on-cycle intermediate extensive mechanistic experiments have been carried out by preparing presumed ruthenacyclic complexes and C-H/D exchange reactions. It suggested that para-cymene ligand is not present in the catalytic on-cycle intermediate and we suspect that metalation occurs with electrophilic ruthenium center via SEAr mechanism. In the second project, we developed the Ru-catalyzed silylation of gramine, tryptamine and their congeners using silanes as coupling partner. The transformation worked well with many different silanes. Regarding directing group, nitrogen atom containing directing groups are more favoured than the oxygen containing directing groups. Wide range of gramines and tryptamines also yielded the desired product in poor to excellent yield. At higher temperature, albeit in low yield, undirected silylation occurred. In order to get some insights about the reaction pathway of the silylation C-H/D exchange experiments were performed, and it revealed the possibility of C4-H activation of gramines by an electron rich metal- Si-H/D experiments showed Si-H activation by Ru is easy. In the final project, we presented the closely related aryne precursors from arylboronic acids via Ru-catalyzed C-H silylation of arylboronates and their selective oxidation. Worthy of note, the aryne capture products obtained from arylboronic acids in a single purification.

This thesis describes the development of a synthetic route that encodes a library of compounds containing medium-sized ring systems, with particular emphasis on the use of oxidative fragmentation and rearrangement strategies. Chapter 1 introduces diversity oriented synthesis (DOS) with particular emphasis on medium-sized ring synthesis and fragmentation/rearrangement protocols to achieve diversity. A more detailed discussion of oxidative fragmentation and rearrangement methods is also presented. Chapter 2 describes strategies for the synthesis of a collection of heterocyclic compounds known as diazabenz[e]aceanthrylenes. The scope of the reaction was explored as a function of a range of substituents and of the ring size of the N-aryl lactam that was used. Spectroscopic observations associated with this set of compounds are also discussed. Chapter 3 describes the development of an m-CPBA-mediated oxidative fragmentation of the diazabenz[e]aceanthrylenes. Analysis of the products from these reactions revealed the presence of atropisomerism due to restricted rotation about the N sp²-C(aryl) sp² bond. Chapter 4 focuses on a related example of oxidative fragmentation from the literature. A previously overlooked stereogenic axis is explored in this system using X-ray crystallographic analysis and variable temperature ¹H NMR spectroscopy. Reinterpretation of the reported mechanism-probing experiment led to the isolation of an alternative isomeric product and an improved interpretation for the reaction outcome is presented. Variable temperature ¹H NMR spectroscopic experiments revealed the energy barrier to racemisation in the medium-sized ring-containing analogues and based on this data the mode of ring inversion is discussed. Chapter 5 describes three rearrangements of the medium-sized ring system created in Chapter 3 including the formation of an azepinoindole ring structure, a Favorskii reaction and spiro-oxindole synthesis. A rationalisation for these reaction outcomes is included along with experimental support of mechanistic proposals. The generality and scope of the reactions are demonstrated including a nucleophile screen. Chapter 6 describes the synthesis of a library of 69 compounds consisting of examples of the core structures described in Chapters 2, 3 and 5. A discussion of the selection process and adaption of the protocol to parallel synthesis is presented. This chapter concludes with preliminary screening of the library against a variety of strains of yeasts and bacteria.

Phosphorus-Selenium chemistry has seen a surge in development over the last five to ten years thanks to the optimisation of the synthesis of 2,4-diphenyl-1,3,2,4-diselenadiphosphetane-2,4-diselenide, Woollins' Reagent. This selenium analogue of the well known Lawesson's Reagent has proved itself to be a valuable asset to modern inorganic chemistry, providing a route to novel heterocycles, as well as acting as a selenation reagent with a wide range of functional groups. A series of new ammonium phenylphosphonamidodiselenoate ligands were synthesised via the reaction of Woollins' Reagent with a range of amines. The products were obtained in high yields and could be used as ligands for the synthesis of novel metal complexes. The reaction of diisopropylamine N-isopropyl-P-phenylphosphonamidodiselenoate with nickel(II) acetate produces a dimeric structure, whilst the reaction with copper(II) acetate yields a beautiful cluster of the form Cu₆Se₃L₆. The phenylphosphonamidodiselenoate ligands were further reacted with a range of cis-Pt(PR₃)₂Cl₂ complexes to form a library of 20 novel compounds, which were studied by ³¹P{¹H}, ⁷⁷Se{¹H} and ¹⁹⁵Pt{¹H} NMR spectroscopy. The X-ray crystal structure of one of these compounds was obtained, which confirmed the atom connectivity and spatial arrangement of the complexes and the geometry around the platinum centre. During investigations into the above-mentioned platinum complexes, it was postulated that an increase in steric bulk of the phosphine ligands would aid crystallisation of the products. As such, trimesityl-, dimesitylphenyl- and mesityldiphenyl phosphine were synthesised and reacted with elemental sulfur and selenium and hydrogen peroxide, as well as Pt(cod)Cl₂ and K₂[PtCl₄], yielding nine new structures, all of which were characterised by X-ray crystallography, ³¹P{¹H}, ¹³C{¹H} and ¹H NMR spectroscopy. Finally Woollins' Reagent was reacted directly with a selection of metal complexes, yielding some new insights into its reactivity with inorganic moieties, which has been relatively sparsely reported until now.

Chapter 1 is a literature review of selected palladium-catalysed aryl C-N and C-S bond forming reactions. The application of these reactions to the synthesis of heterocycles is also discussed. Chapter 2 highlights the importance of the benzimidazole motif and gives a brief discussion of the existing routes to this scaffold. The utility of N-(o-halophenyl)imidoyl chlorides and imidates as precursors to heterocycles is demonstrated in a palladium-catalysed reaction with N-nucleophiles to afford benzimidazole products. Chapter 3 provides a brief introduction to the synthesis of benzothiazoles and describes efforts towards the use of our established substrates for the preparation of these heterocycles. This is achieved via reaction of N-(o-chlorophenyl)imidoyl chlorides with a sulfur nucleophile in a metal-free process. Chapter 4 is a literature review of palladium-catalysed carbonylation chemistry with specific focus on aminocarbonylation and thiocarbonylation reactions of aryl halides. Heterocycle syntheses which employ such carbonylative methods are also discussed. Chapter 5 describes existing protocols for the synthesis of quinazolinones. A novel palladium-catalysed synthesis of these heterocycles from the reaction of our imidate substrates with an amine and carbon monoxide is described. This further demonstrates their utility as general heterocycle precursors

O presente trabalho divide-se em três capítulos: Capítulo I - Nova síntese de ?-xiloidona: rearranjo de Claisen em hidroxinaftoquinonas; Capítulo II - Síntese e estudo de reatividade de promissores núcleos heteroaromáticos subexplorados pela química medicinal; Capítulo III - Análise computacional de similaridade e propriedades físico-químicas dos núcleos heterocíclicos do capítulo II. O capítulo I descreve uma nova rota para a síntese de ?-xiloidona, um produto natural relacionado ao lapachol, subexplorado pela química medicinal. Esta rota é baseada no rearranjo propargílico de Claisen, a partir da reação de lausona com 3-cloro-3- metilbutino sob catálise de CuCl2/I2.Este capítulo também descreveu a síntese de um derivado furano naftoquinoidal, o qual pode ser utilizado como precursor de ?- duniona, via rearranjo de Claisen aril-alílico. Além da realização desta metodologia substituindo o 3-cloro-3-metilbutino por cinco diferentes alcinos. Este novo processo ofereceu como vantagens principais o menor custo dos catalisadores empregados, os rendimentos melhorados e o reduzido número de etapas reacionais em relação as rotas descritas na literatura para obtenção de?-xiloidona. O Capítulo II apresenta o desenvolvimento de métodos sintéticos novos e eficazes para 3 núcleos heterocíclicos (naftiridinona, pirazolopiridinona e dihidropirrolopirazinona) pouco explorados pela química medicinal porém com potencial para descoberta de fármacos. Buscando abranger metodologias orientadas pela diversidade, neste capítulo foi realizado um estudo preliminar de reatividade destes núcleos frente diferentes abordagens, tanto frente métodos diretos de arilação quanto metodologias clássicas de modificação de anéis aromáticos. Além disso, no capítulo III foram realizados estudos de similaridade para a obtenção de padrões estruturais que possam ser aplicados em programas de descoberta de fármacos assim como o estudo de propriedades físico-químicas dos núcleos do capítulo II. Todo este trabalho permitiu desenvolver 10 moléculas inéditas na literatura, bem como novas metodologias para a síntese de compostos previamente descritos. / The present work is divided in two chapters: Chapter I - New synthesis of ? - xiloidone: Claisen rearrangement of hydroxynaphthoquinones; Chapter II - Synthesis and reactivity study of promising heteroaromatic coresunderstudied by medicinal chemistry; Chapter III - Similarity and physic-chemical properties analysis of the heterocyclic cores from chapter II. Chapter I describes a newsynthetic route to?- xiloidona, which isa natural product related to lapachol and understudied by medicinal chemistry. This route is based on propargyl Claisen rearrangement from the reaction of lawsone and 3-chloro-3- methylbutynemediated by CuCl2/I2. This chapter also describes the synthesis of a furan derivative which can be used as?- dunnione precursor. Also this methodology had been applied replacing the 3-chloro- 3-methyllbutynefor five different alkynes. This new process is associated with lower cost, improved yields and reduced number of reaction steps when compared to the literature. The chapter II aimed at the development of synthetic methods to obtain 3 heterocyclic cores(naphthyridinone, pyrazolopyridinoneand dihydropyrrolopyrazinone)with drug discovery potential but also understudied by medicinal chemistry. Diversity-oriented methodologies had been performedresulting in a reactivity study of these cores across severalsynthetic approaches. Furthermore, the chapter III described the similarity studies that were conducted aiming to obtain structural patterns that can be applied in drug discovery programs. This work describes the development of 10 non-published molecules as well as new methodologies for the synthesis of these previously described compounds.

Aza-heterocycles such as pyridines, imidazoles, piperidines, etc. are ubiquitous structural motifs found in various natural products and pharmacologically active compounds. Thus, they are of unparalleled importance to synthetic, medicinal, and materials chemists. Despite their structural significance, organic transformations available for the functionalization of these heterocycles remain underdeveloped. The development of several synthetic methods to construct aza-heterocyclic building blocks is described in this thesis, which, in turn, should facilitate the assembly of more elaborate frameworks present in bioactive molecules. An intramolecular palladium catalyzed Mizoroki-Heck cyclization of 4-alkylidene dihydropyridines with tethered aryl iodide electrophiles is demonstrated. This provides access to substituted isoindolinones and oxindoles in high yields. An asymmetric variant of this reaction using chiral phosphine ligands delivers enantioenriched oxindoles and isoindolinones. Additionally, an intramolecular Mizoroki-Heck reaction for the synthesis of 2-substituted pyridine derivatives is also developed. An array of fused isoindolinones is constructed as a mixture of diastereomers and further manipulated using chemical transformations to yield the corresponding pyridine and piperdine derivatives. Moreover, a formal [3+2] cyclocondensation of alkylidene dihydropyridines and aryl diazonium salts has been discovered for the synthesis of triazole derivatives. Tertiary amides deliver substituted 1,2,4-triazolium salts, whereas, secondary amides provide substituted, neutral 1,2,4-triazoles in excellent yields, under mild reaction conditions. Furthermore, an intramolecular direct arylation of 2- and 4-substituted alkylpyridines is developed for the synthesis of 2,3- and 3,4-cyclized pyridines. It is shown that 4-alkylpyridines tethered to aryl halides participate in a palladium catalyzed direct arylation to give fused 7-membered lactams in excellent yields. Lastly, an intramolecular cyclization of 1,2-alkylimidazoles is reported. Alkylidene imidazolines tethered to electrophilic keto-amide sidechains participate in an aldol-like reaction to yield γ-lactam products in good yields as mixtures of diastereomers.