Magister Scientiae - MSc / Over the years, Giles and co-workers have established that, upon treatment with potassium tert-butoxide, tetra-substituted naphthalenes undergo cyclisations to afford naphthopyrans. It was suggested that these base-induced cyclisations was as a result of the reacting centers being forced into close proximity as a consequence of steric crowding. This thesis describes the synthesis of 3-allyl-4-ethyl-2-(1′-hydroxyethyl)-1-methoxy-naphthalene 177 and its behaviour towards Pd(0) and potassium tert-butoxide under aerobic and anaerobic conditions, to verify whether the base-promoted cyclisations are indeed caused by the steric influences of the substituents. Two synthetic routes were attempted in the synthesis of the target naphthalene 177. The first of these attempted routes involved the conversion of 2-acetyl-4-hydroxy-1-methoxynaphthalene 182 into 2-acetyl-1-methoxy-4-trifluoromethanesulphonyloxy-naphthalene 191 and subsequently into 2-acetyl-4-ethyl-1-methoxynaphthalene 192 via Stille coupling. However, the subsequent Snieckus ortho-directed metalation reactions on the reduced 4-ethyl-2-(1′-hydroxyethyl)-1-methoxynaphthalene 193, and analogues of it, to afford naphthalene 177 were unsuccessful. The second route entailed a Claisen rearrangement of the tri-substituted 2-acetyl-4-allyloxy-1-methoxynaphthalene 209 to afford the unstable tetra-substituted 2-acetyl-3-allyl-4-hydroxy-1-methoxynaphthalene 210, which was immediately converted into the corresponding 2-acetyl-3-allyl-1-methoxy trifluoromethanesulpholnyloxynaphthalene 211. Stille coupling of the triflate 211 gave the 2-acetyl-3-allyl-4-ethyl-1-methoxy-naphthalene 212, which was subsequently reduced to the target naphthalene alcohol 177.The base-induced cyclisation studies performed on naphthalene 177, confirmed the hypothesis that these cyclisations of terta-substituted naphthalenes are indeed as a result of steric crowding. / South Africa

Over the years, Giles and co-workers have established that, upon treatment with potassium tert-butoxide, tetra-substituted naphthalenes undergo cyclisations to afford naphthopyrans. It was suggested that these base-induced cyclisations was as a result of the reacting centers being forced into close proximity as a consequence of steric crowding.<br /> <br /> This thesis describes the synthesis of 3-allyl-4-ethyl-2-(1&prime / -hydroxyethyl)-1-methoxy-naphthalene 177 and its behaviour towards Pd(0) and potassium tert-butoxide under aerobic and anaerobic conditions, to verify whether the base-promoted cyclisations are indeed caused by the steric influences of the substituents. Two synthetic routes were attempted in the synthesis of the target naphthalene 177. The first of these attempted routes involved the conversion of 2-acetyl-4-hydroxy-1-methoxynaphthalene 182 into 2-acetyl-1-methoxy-4-trifluoromethanesulphonyloxy-naphthalene 191 and subsequently into 2-acetyl-4-ethyl-1-methoxynaphthalene 192 via Stille coupling. However, the subsequent Snieckus ortho-directed metalation reactions on the reduced 4-ethyl-2-(1&prime / -hydroxyethyl)-1-methoxynaphthalene 193, and analogues of it, to afford naphthalene 177 were unsuccessful. The second route entailed a Claisen rearrangement of the tri-substituted 2-acetyl-4-allyloxy-1-methoxynaphthalene 209 to afford the unstable tetra-substituted 2-acetyl-3-allyl-4-hydroxy-1-methoxynaphthalene 210, which was immediately converted into the corresponding 2-acetyl-3-allyl-1-methoxy-4-trifluoromethanesulpholnyloxynaphthalene 211. Stille coupling of the triflate 211 gave the 2-acetyl-3-allyl-4-ethyl-1-methoxy-naphthalene 212, which was subsequently reduced to the target naphthalene alcohol 177.<br /> The base-induced cyclisation studies performed on naphthalene 177, confirmed the hypothesis that these cyclisations of terta-substituted naphthalenes are indeed as a result of steric crowding.

Over the years, Giles and co-workers have established that, upon treatment with potassium tert-butoxide, tetra-substituted naphthalenes undergo cyclisations to afford naphthopyrans. It was suggested that these base-induced cyclisations was as a result of the reacting centers being forced into close proximity as a consequence of steric crowding.<br /> <br /> This thesis describes the synthesis of 3-allyl-4-ethyl-2-(1&prime / -hydroxyethyl)-1-methoxy-naphthalene 177 and its behaviour towards Pd(0) and potassium tert-butoxide under aerobic and anaerobic conditions, to verify whether the base-promoted cyclisations are indeed caused by the steric influences of the substituents. Two synthetic routes were attempted in the synthesis of the target naphthalene 177. The first of these attempted routes involved the conversion of 2-acetyl-4-hydroxy-1-methoxynaphthalene 182 into 2-acetyl-1-methoxy-4-trifluoromethanesulphonyloxy-naphthalene 191 and subsequently into 2-acetyl-4-ethyl-1-methoxynaphthalene 192 via Stille coupling. However, the subsequent Snieckus ortho-directed metalation reactions on the reduced 4-ethyl-2-(1&prime / -hydroxyethyl)-1-methoxynaphthalene 193, and analogues of it, to afford naphthalene 177 were unsuccessful. The second route entailed a Claisen rearrangement of the tri-substituted 2-acetyl-4-allyloxy-1-methoxynaphthalene 209 to afford the unstable tetra-substituted 2-acetyl-3-allyl-4-hydroxy-1-methoxynaphthalene 210, which was immediately converted into the corresponding 2-acetyl-3-allyl-1-methoxy-4-trifluoromethanesulpholnyloxynaphthalene 211. Stille coupling of the triflate 211 gave the 2-acetyl-3-allyl-4-ethyl-1-methoxy-naphthalene 212, which was subsequently reduced to the target naphthalene alcohol 177.<br /> The base-induced cyclisation studies performed on naphthalene 177, confirmed the hypothesis that these cyclisations of terta-substituted naphthalenes are indeed as a result of steric crowding.

Abstract This thesis is divided into two parts. Part one presents a novel method for the synthesis of naphthalenes bearing aryl substituents. The novel route starts from three simple and readily available tetralones, α-tetralone, 6-methoxy-α-tetralone and 6,7-dimethoxy-α- tetralone. By means of standard Suzuki coupling methodology and aromatization methods, twelve aryl-substituted naphthalenes were synthesized from the tetralones over five steps in good yields. Some of the aryl-substituted naphthalenes synthesized have shown positive results when tested against malignant cancer cells. Part one also explains how unexpected cyclopropa[a]naphthalenes were obtained from 1-aryl-3,4-dihydro-2- naphthaldehydes by treatment with lithium aluminium hydride. The methodology developed in part one is further explored in part two of the thesis, which describes the synthesis of analogues of [1,1’]binaphthalenyl-2,2’-diol. A small library of twelve different biaryl diols was prepared from simple bromo(methoxy)naphthaldehydes that were synthesized in part one. The resultant biaryl diols were used in the design of twenty-two novel phosphite, phosphate, phosphoramidite and phosphoramidate ligands in which the phosphorus atoms are contained in either a nine-or an eight-membered heteroatom ring. However, these ligands are still to be tested in metal-catalyzed hydrogenation reactions.

No description available.

No description available.

A new method for the synthesis of naphthalenes has been recently discovered. The Atom Transfer Radical Cyclisation (ATRC) of diverse 2-allylphenyl2',2',2'-trichloroacetates in the presence of a Cu complex afford schloronaphthalenes in good yields using either microwave or thermolytic methods of activation. A mechanism for the benzannulation reaction is proposed and experiments presented in order to validate this hypothesis. The use of 1,3-bis(2,6-diisopropylphenyl)imidazolium copper(I) chloride [(IPr)CuCl)] along with other metal carbenes is compared to the already reported CuCl/ligand system. Since the scope and synthetic utility of this new benzannulation reaction is restricted due to the use of the MW reactor, a solvent in which the thermal reaction can take place is reported, proving its efficiency in the synthesis of a range of substituted naphthalenes. The potential and versatility of the benzannulation reaction has been investigated. Studies towards the synthesis of gilvocarcin M which contains a tetracyclicaromatic core are presented. Gilvocarcins have potential use as anti-cancer agents and represent a member of the C-aryl glycosides found in natural products. Gilvocarcin M is a challenging target because there are a sparse number of total syntheses reported in the literature. The ATRC reaction of (vinyl)phenyl trichloroacetate has also been investigated, affording the synthesis of functionalised coumarins. The mechanism of this reaction has also been investigated, establishing that, in some cases, aretro-Kharasch reaction is observed.

No description available.

In the transition to a sustainable energy supply there is an increasing need to use biomass for replacement of fossil fuel. A key challenge is to utilize biomass conversion technologies in an environmentally sound manner. Important aspects are to minimize potential formation of persistent organic pollutants (POPs) such as dioxins and dioxin-like compounds. This thesis involves studies of formation characteristics of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs) in microwave-assisted pyrolysis (MAP) and torrefaction using biomass as feedstock. The research focuses are on their levels, distributions, fingerprints (homologue profiles and isomer patterns) and the underlying formation pathways. The study also included efforts to optimize methods for extracting chlorinated aromatic compounds from thermally treated biomass. The overall objective was to contribute better understanding on the formation of dioxins and dioxin-like compounds in low temperature thermal processes. The main findings include the following: Pressurized liquid extraction (PLE) is applicable for simultaneous extraction of PCDDs, PCDFs, PCNs, polychlorinated phenols and benzenes from thermally treated wood. The choice of solvent for PLE is critical, and the extraction efficiency depends on the degrees of biomass carbonization. In MAP experiments PCDDs, PCDFs and PCNs were predominantly found in pyrolysis oils, while in torrefaction experiments they were mainly retained in solid chars with minor fractions in volatiles. In both cases, highly chlorinated congeners with low volatility tended to retain on particles whereas the less chlorinated congeners tended to volatize into the gas phase. Isomer patterns of PCDDs, PCDFs and PCNs generated in MAP were more selective than those reported in combustion processes. The presence of isomers with low thermodynamic stability suggests that the pathway of POPs formation in MAP may be governed not only by thermodynamic stabilities but also by kinetic factors. Formation of PCDDs, PCDFs and PCNs depends not only on the chlorine contents in biomass but also the presence of metal catalysts and organic/metal-based preservatives. Overall, the results provide information on the formation characteristics of PCDDs, PCDFs and PCNs in MAP and torrefaction. The obtained knowledge is useful regarding management and utilization of thermally treated biomass with minimum environmental impact.

Polycyclic aromatic hydrocarbon (PAH) formation and growth from cyclopentadiene (CPD) moieties have been investigated using a laminar flow reactor and molecular modeling. The resonance-stabilized cyclopentadienyl radical is readily formed in flames and can participate in PAH growth to soot by reaction with the ??onds of aromatic species. Both CPD pyrolysis and computational results indicate that formation of indene and benzene is favored at low temperatures (below 750oC) and formation of naphthalene is favored at high temperatures. Reaction pathways from CPD have further been extended to PAH formation from the reaction of CPD and aromatic compounds with different types of ??onds. Results indicate that, while the major products from the pyrolysis of CPD, acenaphthylene, styrene and phenanthrene mixtures are from the reaction of CPD to itself rather than to these aromatic compounds with different ??onds, CPD does add to these compounds to produce larger PAH. Polychlorinated naphthalene (PCN) formation from chlorinated phenols has also been studied. In combustion exhaust gas, chlorinated phenols can produce dioxin as well as PCNs. PCN and polychlorinated dibenzofuran (PCDF) congener product distributions were consistent with proposed pathways involving phenoxy radical coupling at unchlorinated ortho-carbon sites. Tautomerization of the phenoxy radical coupling and subsequent fusion via H2O loss results in PCDF formation. Competing with this reaction pathway, CO elimination and subsequent fusion via hydrogen and/or chlorine loss was found to produce PCNs. PCDF isomer distributions were found to be weakly dependent to temperature, whereas PCN isomer distributions were found to be more temperature sensitive with selectivity to particular isomers decreasing with increasing temperature. Results of this research contribute to a better understanding of chemical mechanisms involved in the formation of toxic byproducts and soot in combustion systems.