This thesis describes the synthesis and chemistry of alkyl 2,3-bis(trimethylstannyl)-2-alkenoates ((78) and (83)). It was shown that these compounds could be readily transformed into useful intermediates for the synthesis of functionalized, stereochemically defined tetrasub-stituted alkenes (87) and tricyclic dienes of general structure (322A). The synthesis and chemistry of compounds (277) and (278) is also described. The palladium(O)-catalyzed addition of hexamethylditin to a variety of α,β-acetylenic esters (90), afforded in a stereoselective manner, the corresponding alkyl (Z)-2,3-bis(trimethylstannyl)-2-alkenoates (83). Subsequent thermolysis of these compounds afforded the corresponding alkyl (E)-2 , 3-bis(trimethylstannyl)-2-alkenoates (78). It was found that treatment of alkyl (E)- and (Z)-2,3-bis(tri-methylstannyl)-2-alkenoates with methyllithium at low temperature, followed by reaction of the resultant nucleophilic intermediate with a variety of alkylating agents, afforded the trisubstituted vinylstannanes (80). On the other hand, successive treatment of methyl w-halo-2,3-bis-(trimethylstannyl)-2-alkenoates (202) with methyllithium and HMPA provided a facile route to cyclic β-trimethylstannyl α,β-unsaturated esters (203). Compounds (80) were readily converted into vinyl iodides of general structure (219) in which W is a functionalized group derived from the CO₂R moiety. These latter compounds served as useful intermediates for the synthesis of functionalized, stereochemically defined tetrasubstituted alkenes (87). For example, treatment of compounds (219) with 1.1 or 2.2 equiv of n-butyllithium at -78°C afforded the corresponding vinyllithium species (86) , which could either be alkylated directly or further transposed into the organocopper(I) reagent (263A) and then alkylated, to afford in each case, the tetrasubstituted alkenes (87). The Pd(0)-catalyzed addition of tri-n-butylstannyltrimethylgermane (276) to a variety of α,β-acetylenic esters (90) afforded the corresponding compounds (277) and (278) in a ratio of approximately 3:1, respectively. Treatment of the (E) isomers (277) with n-butyllithium at -98°C, followed by alkylation of the resultant nucleophilic intermediate afforded the corresponding trisubstituted vinylgermanes (293). One of these latter compounds was readily converted into the iodo bromide (308), which is potentially synthetically equivalent to the d,a synthon (310). When the enolate anion of compounds (203) was successively treated with HMPA and compound (308) the esters (311) were obtained. The Pd(0) catalyzed intramolecular coupling of the vinylstannane-vinyl iodide moieties of (311) provided a facile route to the bicyclic triene esters (312). Similarly, alkylation of the enolate anion of compounds (203) with (325) (which was readily obtained from (203), in which n - 1), followed by the Pd(0)-catalyzed coupling of the resulting alkylated material afforded the tricyclic diene esters (322A). [Formula Omitted] / Science, Faculty of / Chemistry, Department of / Graduate

No description available.

Les alcanes et les alcènes sont des hydrocarbures non cycliques important dans l’industrie. Ils sont synthétisés à partir d'acides gras par une grande variété d’organismes mais les connaissances à ce sujet sont très limitées chez les microalgues. Le but de ces travaux était donc de rechercher la présence d’alcanes ou d’alcènes dans diverses microalgues modèles, et d’essayer d’identifier la ou les enzymes responsables de la synthèse de ces composés. Nous avons mis en évidence la présence d’hydrocarbures linéaires en C15-C17 chez les microalgues Chlorella et Chlamydomonas. Ces composés étaient synthétisés uniquement en présence de lumière. L’absence dans le génome de ces microalgues d’homologues de gènes codant pour des enzymes connues de synthèse d’alcanes/alcènes a permis de conclure à la présence d’un nouveau système de synthèse d’hydrocarbures. Des purifications enzymatique et des analyses protéomique ont permis d’identifier une enzyme candidate qui exprimée chezE. coli est suffisante à la synthèse d’hydrocarbures. L'étude de cette enzyme révella qu'il s'agissait d'une photoenzyme utilisant l'énergie des photons bleue pour décarboxyler les acides grass en alca(e)ne. La structure de cette photoenzyme montre la présence un tunnel hydrophobe contenant l’acide gras et le cofacteur FAD. Cette nouvelle enzyme nommée « alcane photosynthase » amène de nombreuses question: qu'elle est la fonction des hydrocarbures chez ces microorganismes? Quel est le mécanisme catalytique de l’alcane photosynthase? Enfin, elle offre de nouvelles possibilités pour la production de biocarburants utilisant directement l’énergie solaire. / Alkanes and alkenes are important in industry. Alkanes and alkenes are synthesized from fatty acids by a variety of organisms, such as plants and insects. However, the presence in microalgae of enzymes converting fatty acids into hydrocarbons has been poorly studied. The aim of this work was to investigate the presence of alkanes and alkenes in various microalgae models, and try to identify the enzymes responsible for the synthesis of these compounds.We have first demonstrated the presence of linear hydrocarbons C15-C17 in microalgae Chlorella and Chlamydomonas. Then we have shown that the main hydrocarbon formed in Chlorella and Chlamydomonas was derived from cis-vaccenic acid and was synthesized only in the presence of light. Absence of homologues of genes coding for known alkane/alkene biosynthetic enzymes in the genome of Chlorella and Chlamydomonas indicate the presence of an unknown pathway. Enzymatic purification and proteomic analysis allowed to identify a candidate enzyme which, expressed in E. coli lead to the formation of hydrocarbons with variable chain lengths, thus demonstrating that it was really an synthase alkane. Characterization showed that the enzyme was a photoenzyme, which used blue light to catalyse the decarboxylation of fatty acid to an alka(e)ne. The three-dimensional structure of this enzyme revealed a hydrophobic tunnel containing the fatty acid and the FAD cofactor.

Thesis (PhD)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: This study concerns the incorporation of adamantane containing monomers 3-(1-adamantyl)-1-propene and 1-(1-adamantyl)-4-vinylbenzene into ethene, propene and higher a-olefins using different catalytic systems. The effect of the incorporation of the adamantane monomer on the physical and thermal properties of the polymers was investigated. A thorough study on the background of adamantane in general, as well as polymerization reactions involving the above-mentioned monomers and a-olefins was done. 3-(1-Adamantyl)-1-propene as well as 1,.(1-adamantyl)-4-vinylbenzene was sucessfully synthesized. The homo polymers of each monomer were made. The above-mentioned monomers were also polymerized: • . 3-( 1-adamantyl)-1-propene with ethene, propene and higher a-olefins, • 1-(1-adamantyl)-4-vinylbenzene with ethene and styrene. The copolymers of 3-(1-adamantyl)-propene as well as 1-(1-adamantyl)- 4-vinylbenzene were characterized as far as possible to show the influence of the incorporation of the adamantane group on the physical and chemical properties of the polymers. A series of 3-phenyl-1-propene copolymers with higher a-olefins were synthesized to compare the influence of the phenyl group to the adamantyl group on the relevant properties of the polymers. / AFRIKAANSE OPSOMMING: Hierdie studie behels die inkorporasie van adamantaan-bevattende monomere, 3-( 1-adamantiel)-1-propeen en 1-(1-adamantiel)-4-vinielbenseen in eteen, propeen en hoër a-olefiene met behulp van verskillende katalitiese sisteme. Die effek wat die inkorporasie van die adamantaan monomeer op die fisiese en chemiese eienskappe van die polimere het, is ondersoek. 'n Deeglike studie van die agtergrond van adamantaan in die geheel, sowel as die polimerisasie reaksies van die bogenoemde monomere met a-olefiene, is gedoen. 3-( 1-Adamantiel)-1-propeen sowel as 1-(1-adamantiel)-4-vinielbenseen is suksesvol berei. Die homopolimere van bogenoemde monomere is gesintetiseer. Bogenoemde monomere is gepolimeriseer: • 3-(1-adamantiel)-1-propeen met eteen, propeen en hoër a-olefiene, • 1-(1-adamantiel)-4-vinielbenseen met eteen en stireen. Die kopolimere van 3-(1-adamantiel)-1-propeen en 1-(1-adamantiel)- 4-vinielbenseen is sover moontlik gekarakteriseer om die invloed van die adamantaan groep op die fisiese en chemiese eienskappe van die polimeer te toon. 'n Reeks kopolimere van 3-(1-feniel)-1-propeen met hoër a-olefiene is gesintetiseer om die verwantskap tussen die invloed van die fenielgroep en die adamantielgroep op die relevante eienskappe van die polimere te toon.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

The reactions of five trihalomethyl group substituted electron-deficient olefins with electron-rich olefins were studied in order to determine the effect of steric bulk upon the subsequent reactions of the tetramethylene intermediates initially formed. Reactions of β-trihalomethyl group substituted olefins yielded cyclobutane adducts, resulting from a gem dimethyl effect which accelerates the collapse of the tetramethylene intermediate. Reactions of α-trihalomethyl group substituted olefins gave both small molecule and polymeric products. Polymers were produced in reactions where steric interactions between the termini of the tetramethylene intermediates prevented ring formation. Ester substituted electron-deficient olefins reacted with electron-rich olefins to give both cyclobutane and 6-alkoxy-3,4-dihydro-2H-pyran derivatives. A transition from concerted to stepwise reaction was observed, resulting from steric hindrance in the transition state leading to [4+2] cycloaddition. Exploratory studies of ion-radical propagation and chain transfer in polymerization processes were also conducted. The acid catalyzed free radical polymerization of imines was attempted, along with chain transfer studies of zwitterion-radical intermediates.

Ph.D. (Chemistry) / Compounds 3-ferrocenylpyrazole (L1) 3-ferrocenyl-5-methylpyrazole (L2) and 4- ferrocenyl-1-methyl diketone (L7) were synthesized according to literature procedure, while compounds 3-ferrocenylpyrazolyl-methylenepyridine (L3), 3-ferrocenyl-5- methylpyrazolyl-methylenepyridine (L4), 3-ferrocenylpyrazolyl-ethyl amine (L5) and 3- ferrocenyl-5-methylpyrazolyl-ethylamine (L6) were prepared by phase transfer alkylation of the 2,6-bis(bromomethyl)pyridine or 2-bromoethylamine with the appropriate ferrocenylpyrazole L1 or L2 in a 1:1 ratio. These compounds L3-L6 show structural isomers labelled a and b. The isomers were in a ratio of 4:1 for L3 and L4 while for L5 and L6 the isomers were 2:1 ratio...

M.Sc. (Chemistry) / Please refer to full text to view abstract