This thesis deals with the development and application of methods for asymmetric olefinations, in particular Horner-Wadsworth-Emmons (HWE) reactions, in the synthesis of certain natural products. Relying on asymmetric HWE reactions to access key building blocks, two natu-ral products, pyranicin and pyragonicin, were synthesized from common late intermediates. The utility of the HWE reactions is highlighted through a desymmetrization of a meso-dialdehyde as well as a stereoconvergent reaction sequence employing the sequential use of a HWE parallel kinetic resolution fol-lowed by a Pd-catalyzed allylic substitution to convergently transform a race-mate to a single stereoisomer of the product. Methodological extensions of these syntheses include a divergent synthesis of 2,3,6-substituted tetrahydropyran derivatives and application of Zn-mediated asymmetric alkynylations to install key stereocenters. Synthetic studies directed towards a more complex target, mucocin, employing a triply convergent strategy, have also been performed. Expedient and reliable routes to three key fragments were developed, as well as methodology to access to all nine stereocenters. The fragment coupling to assemble the oligonuclear core still remains a challenge, however. Key features of the synthesis include the formation of two fragments from a common precursor derived from an asymmetric HWE desymmetrization, Zn-mediatedated asymmetric alkynylations, a stereoselective oxa-Michael cyclization dependent on a simultaneous protective group migration and a one-pot procedure for the synthesis of a TBS protected iodohydrin from a terminal epoxide. An investigation of the possibilities for developing a transition metal catalyzed asymmetric olefination using a chiral Re-complex is outlined. An enantioen-riched BINAP-Re complex was synthesized and characterized by X-ray. An efficient protocol for the olefination of functionalized aldehydes employing this catalyst was developed, but gave racemic products in two attempted kinetic resolutions of racemic substrates, most likely due to a reaction pathway proceeding via a non-metal associated phosphonium ylide. / QC 20100921

Ce travail s’inscrit dans la recherche de nouveaux 5-nitroimidazoles fonctionnalisés à visée thérapeutique. L’étude de la réactivité du 4-bromo-1,2-diméthyl-5-nitro-1H-imidazole vis-à-vis des réactions de couplages de Suzuki, Sonogashira et Stille a permis la synthèse de nouveaux 5-nitroimidazoles substitués en position 4. Par ailleurs, un couplage de Suzuki régiosélectif a pu être mis au point sur le 2,4-dibromo-1-méthyl-5-nitro-1H-imidazole permettant l’accès en une seule étape à des composés substitués à la fois en positions 2 et 4. Parmi les composés synthétisés via ces couplages pallado-catalysés, les dérivés chlorométhylés conjugués avec le groupement nitro ont été utilisés en tant que substrats pour l’étude de réactions par transfert monoélectronique (SRN1, TDAE). Ainsi, dans une seconde partie, nous décrivons la réaction entre le 4-(3-chloroprop-1-ynyl)-1,2-diméthyl-5-nitro-1H-imidazole et plusieurs anions nitronates dans des conditions de SRN1. Cette réactivité a pu être étendue au 2,4-bis(3-chloroprop-1-ynyl)-1-méthyl-5-nitro-1H-imidazole permettant la réalisation d’une bis-SRN1. La méthodologie TDAE a été mise en œuvre sur le 4-(3-chloroprop-1-ynyl)-1,2-diméthyl-5-nitro-1H-imidazole, avec de faibles rendements observés, contrairement à ceux obtenus avec le (E)-4-[4- (chlorométhyl)styryl]-1,2-diméthyl-5-nitro-1H-imidazole sur lequel plusieurs types d’électrophile ont pu être additionnés. Enfin, le pouvoir mutagène, ainsi que le potentiel de réduction des 5-nitroimidazoles synthétisés ont été déterminés. L’évaluation anti-infectieuse est actuellement en cours sur des souches de Giardia lamblia et sur une grande variété de bactéries anaérobies strictes. / This work focuses on the synthesis of novel functionalized 5-nitroimidazoles possessing therapeutic activities. New 4-substituted-5-nitroimidazoles were obtained using Suzuki, Stille or Sonogashira cross-coupling using the 4-bromo-1,2 dimethyl-5-nitro-1H-imidazole. Moreover, access to functionalized products at both 2 and 4 positions of imidazole ring was developed thanks to a regioselective Suzuki cross-coupling on the 2,4-dibromo-1-methyl-5-nitro-1H-imidazole. Among cross-coupling products, those possessing chloromethyle substituent conjugated with the nitro group, were employed as starting material in the single electron transfer reaction (SRN1, TDAE) studies. Therefore, in a second part, we described the reaction between the 4-(3-chloroprop-1-ynyl)-1,2-dimethyl-5-nitro-1H-imidazole and several nitronate anions in SRN1 conditions. This reactivity was applied to the 2,4-bis(3-chloroprop-1-ynyl)-1-méthyl-5-nitro-1H-imidazole allowing the formation of bis-SRN1 products. TDAE methodology was implemented on the 4-(3-chloroprop-1-ynyl)-1,2-dimethyl-5-nitro-1H-imidazole, however poor yields were observed. TDAE strategy on the (E)-4-[4-(chlorométhyl)styryl]-1,2-diméthyl-5-nitro-1H-imidazole were more successful, addition products with different electrophilic species were obtained. Finally, mutagenic power and potential of reduction of synthesized 5-nitroimidazole were assayed. The anti-infective properties of these novel 5-nitroimidazole are currently under investigation.

Thesis advisor: Amir H. Hoveyda / Chapter 1. Through the use of quantum theory of atoms in molecules (QTAIM) the similarities and differences between transition metal complexes ligated by phosphines and N-heterocyclic carbenes (NHC) were elucidated. Among the key findings, the phosphines were identified as stronger charge donors than NHCs; however, the latter class of ligands exhibits a weaker p-accepting character than the former. Furthermore, Tolman electronic parameter (TEP) was determined to be an inadequate gauge for the total electron donating ability of phosphines and NHCs; rather TEP can serve as a measurement of population of dp set of orbitals of a metal center in question. Computational and experimental studies of the mechanism of NHC-catalyzed boron and silicon addition to a,ß-unsaturated carbonyls reactions were carried out. Through the use of radical traps the mechanisms involving homolytic cleavage of B-B or B-Si bonds were ruled out. Computational (DFT) studies of the mechanism identified two pathways: (1) direct activation of diboron or borosilyl reagents through coordination of NHC to the B atom, (2) net oxidative addition of the diboron or borosilyl reagents to the carbon (II) of the NHC. The insights gained from the aforementioned studies were employed to rationalize the observed lack of reactivity of NHC-activated diboron complexes in the presence of aldehydes. Chapter 2. New C(1)-symmetric chiral monodentate N-heterocyclic carbenes were prepared, and corresponding chiral Ru-carbene complexes were synthesized. These complexes were employed to gain empirical understanding of factors that govern stereoselectivity in Ru-catalyzed enantioselective olefin ring-closing metathesis. The data thus obtained was employed to infer that syn-to-NHC reaction pathways are competitive and non-selective. One plausible mechanism, through which syn-to-NHC pathways can be accessed, involves Berry pseudorotations. Through the use of stereogenic-at-Ru complexes diastereomeric Ru-carbenes were isolated (silica gel chromatography) and spectroscopically characterized in solution phase. The diastereomeric Ru-carbenes were found to undergo non-metathesis stereomutations at Ru center, thereby providing additional support for the above hypothesis regarding accessibility of syn-to-NHC olefin metathesis pathways. Non-metathesis stereomutation at Ru was found to be accelerated in the presence of protic additives, suggesting the plausibility of hydrogen bonding between the acidic proton and the X-type ligands on Ru. Occurrence of hydrogen bonding was corroborated through the use of chiral allylic alcohols in Ru-catalyzed diastereoselective ring-opening/cross metathesis, which was developed into a versatile method for highly diastereoselective functionalization of terminal olefins. / Thesis (PhD) — Boston College, 2011. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Thesis advisor: Amir H. Hoveyda / Chapter 1. Mechanistic Insights and Factors Influencing Polytopal Rearrangements in Stereogenic-at-Ru Carbenes. Herein, the mechanistic elucidation of the stereochemical inversion in stereogenic-at-Ru carbene complexes through olefin metathesis (OM) and non-olefin metathesis (non-OM) based polytopal rearrangements is provided. Our investigations involve the isolation and characterization of previously hypothesized higher-energy (e.g., endo-anti) and lower-energy (e.g., exo-anti) diastereomers, and their interconversion under thermal and/or acid-catalyzed conditions is demonstrated. Furthermore, our computational efforts highlighting the importance of the anionic ligands, due to their critical role in trans influence, dipolar interactions, and e-e repulsions, in polytopal rearrangements are reported. Finally, the positive influence of H-bonding in OM and non-OM processes is also rationalized. (a) Khan, R. K. M.; Zhugralin, A. R.; Torker, S.; O'Brien, R. V.; Lombardi, P. J. and Hoveyda, A. H. "Synthesis, Isolation, Characterization, and Reactivity of High-Energy Stereogenic-at-Ru Carbenes: Stereochemical Inversion Through Olefin Metathesis and Other Pathways," J. Am. Chem. Soc. 2012, 134, 12438-12441. (b) Torker, S.; Khan, R. K. M. and Hoveyda, A. H. "The Influence of Anionic Ligands on Stereoisomerism of Ru Carbenes and Their Importance to Efficiency and Selectivity of Catalytic Olefin Metathesis Reactions," J. Am. Chem. Soc. 2014, 136, 3439-3455. Chapter 2. Highly Z- and Enantioselective Ring-Opening/Cross-Metathesis of Enol Ethers Through Curtin-Hammett Kinetics. The first instances of Z- and enantioselective Ru-catalyzed olefin metathesis are presented. Ring-opening/cross-metathesis (ROCM) reactions of oxabicyclic alkenes and enol ethers and a phenyl vinyl sulfide are promoted by 0.5-5.0 mol % of enantiomerically pure stereogenic-at-Ru complexes with an aryloxy chelate tethered to the N-heterocyclic carbene. Products are formed efficiently and with exceptional enantioselectivity (up to >98:2 enantiomer ratio). Surprisingly, the enantioselective ROCM reactions proceed with high Z selectivity (up to >98% Z). Moreover, reactions proceed with the opposite sense of enantioselectivity versus aryl olefins, which afford E- isomers exclusively. DFT calculations and deuterium-scrambling experiments, indicating fast interconversion between endo- and exo-Fischer carbene diastereomers, support a Curtin-Hammett situation. On this basis, models accounting for the stereoselectivity levels and trends are provided. Furthermore, the correlation of Fischer carbene character to the observed chemoselectivity in ROCM with enol ethers is also disclosed. Finally, a general proposal for the substrate-controlled Z selectivity in OM is also discussed. (a) Khan, R. K. M.; O'Brien, R. V.; Torker, S.; Li, B. and Hoveyda, A. H. "Z- and Enantioselective Ring-Opening Cross-Metathesis with Enol Ethers Catalyzed by Stereogenic-at-Ru Carbenes: Reactivity, Selectivity, and Curtin-Hammett Kinetics," J. Am. Chem. Soc. 2012, 134, 12774-12779. (b) Torker, S.; Koh, M. J.; Khan, R. K. M. and Hoveyda, A. H. "Origin of Z selectivity in Olefin Metathesis Reactions of Certain Terminal Alkenes Catalyzed by Typically E-Selective Ru Carbenes," manuscript submitted. Chapter 3. A New Class of Highly Efficient Ru Catalysts for Z-Selective Olefin Metathesis. Herein, we outline a general design for Z-selective OM, which led to the development of a new class of stereogenic-at-Ru carbene complexes (Ru4-9). Furthermore, we demonstrate that the newly developed dithiolate complexes Ru4b and Ru5 efficiently promote high activity and selectivity in ROMP reactions of norbornene and cyclooctene. Notably, the catechothiolate Ru4b catalyzes Z-selective ROCM with a broad scope of alkenes involving various functional groups (e.g., alcohols, enol ethers, vinyl sulfides, amides, heterocycles, and conjugated 1,3-dienes). More importantly, we disclose that the catecholate complex Ru4a is kinetically non-selective in OM and readily decomposes in the presence of mildly acidic moieties (e.g., alcohols and CDCl3). Subsequently, Ru9 is developed to efficiently promote highly Z-selective CM of a diol cross-partner with a wide range of alkene substrates. Most remarkably, the aforementioned protocol is employed in two natural product syntheses and the OM-based Z-selective cracking of oleic acid, which is unprecedented with existing Ru-carbenes and Mo/W-alkylidenes. (a) Khan, R. K. M.; Torker, S. and Hoveyda, A. H. "Readily Accessible and Easily Modifiable Ru-Based Catalysts for Efficient and Z-Selective Ring-Opening Metathesis Polymerization and Ring-Opening Cross-Metathesis," J. Am. Chem. Soc. 2013, 135, 10258-10261. (b) Koh, M. J.; Khan, R. K. M.; Torker, S. and Hoveyda, A. H. "Broadly Applicable Z- and Diastereoselective Ring-Opening/Cross-Metathesis Catalyzed By a Dithiolate Ru Complex," Angew. Chem., Int. Ed. 2014, 53, 1968-1972. (c) Khan, R. K. M. ; Torker, S. and Hoveyda, A. H. "Reactivity and Selectivity Differences Between Catecholate and Catechothiolate Ru Complexes. Implications Regarding Design of Stereoselective Olefin Metathesis Catalysts," J. Am. Chem. Soc. 2014, 136, 14337-14340. (d) Koh, M. J.; Khan, R. K. M.; Torker, S.; Yu, M.; Mikus, M. S. and Hoveyda, A. H. "Synthesis of High-Value Alcohols, Aldehydes and Acids by Catalytic Z-Selective Cross-Metathesis" manuscript submitted. / Thesis (PhD) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

Im Rahmen dieser Dissertation wurde die säurekatalysierte Tandem-Aldol-MPV-Reaktion zur Darstellung von 1,3-Diolethern als Eintopfverfahren entwickelt. Dabei konnte ein Syntheseprotokoll entwickelt werden, das durch geschickte Wahl der Reaktionspartner, eines Katalysatorsystems aus LiClO4/ Trifluoressigsäure und geeigneter Reaktionsbedingungen ermöglichte, die klassische dreistufige Synthese von 1,3-Diolethern auf ein effizientes Eintopfverfahren zu reduzieren. Die Kombination mit umfangreichen mechanistischen Untersuchungen ermöglichte erstmals die Entwicklung einer asymmetrischen Variante der Tandem-Aldol-MPV-Reaktion. Dabei hat sich eine Kombination von chiralem Menthol und Methanol bewährt, wodurch die Reaktion mit hoher Chemoselektivität und ohne Konkurrenzreaktionen abläuft. Mit Hilfe dieser neuen Reaktionsbedingungen der asymmetrischen Tandem-Aldol-MPV-Reaktion gelang erstmals die Synthese von chiralen 1,3-Diolethern mit sehr guter Regio- und guter bis sehr guter Diastereo- und Enantioselektivität. Bemerkenswert ist die Möglichkeit der Steuerung der asymmetrischen Synthese und damit des selektiven Zugangs zu jeweils einem Enantiomer durch Variation zwischen (-)- bzw. (+)-Menthol. Als Erweiterung gelang erstmals eine intramolekulare Tandem-Aldol-MPV-Reaktion mit der Synthese verschieden substituierter pentacyclischer 1,3-Diolether. Auch hier gelang die Synthese ausgehend von zuvor synthetisierten Dialdehyden in einer Eintopfreaktion mit sehr hoher Diastereoselektivität. Auf dem zweiten großen Gebiet der Dissertation konnte eine neue innovative Syntheseroute zu Verbindungen in der Thiochromanreihe mit völlig neuartigem Substitutionsmuster entwickelt werden. Es gelang die Entwicklung einer milden Eintopfsynthese, die die Synthese hochsubstituierter anti-konfigurierter Thiochromane ermöglicht. Dabei gelang die Synthese eines Thiochromans ausgehend von racemischen Edukten, in dem stereoselektiv drei benachbarte Stereozentren aufgebaut wurden. / In this thesis, the acid-catalyzed tandem-aldol-Meerwein-Ponndorf-Verley-reaction for the preparation of 1,3-diolethers was developed. By handy choice of the reactants, the LiClO4/ trifluoroacetic acid catalyst system and appropriate reaction conditions an efficient one-pot-reaction protocol has been established. The development of an asymmetric execution was enabled by employing extensive mechanistic examinations. Consequently, a combination of chiral menthol and methanol leads to products with high chemoselectivities and without occurrence of competitive reactions. For the first time, by employing the novel optimized synthetic scheme for the asymmetric tandem-aldol-MPV reaction, chiral 1,3-diolethers have been prepared with very high regio- and moderate to very high diastereo- as well as enantioselectivity. Moreover, an opportunity for controlling asymmetric synthesis by variation of (-)- and (+)-menthol was developed. Hence, a selective access to the desired enantiomer is given. In continuative work an intramolecular tandem-aldol-MPV-reaction for the preparation of highly substituted penta-cyclic 1,3-diolethers was developed. Also in this case, the reaction was realized as an one-pot reaction with high anti-diastereoselectivity. The second chapter of this thesis describes a new innovative synthesis of thiochromans with completely unknown substitution pattern. We were able to establish a mild one-pot synthesis of highly substituted anti-configured thiochromans. As a special highlight we suceeded in the steroeselective synthesis of a thiochroman with three adjacent stereogenic centers starting from racemic educts.

No description available.

Carbon nanoribbons are today of great interest as graphene segments with modulable electronic properties. Whilst top down techniques give giant ribbons, bottom-up organic synthesis may lead to exactly designed nanoribbons of controlled geometries. The Scholl reaction is a precious chemical tool for that purpose since it yields efficiently to the graphitization of long and flexible polyphenylene precursors.Surprisingly, twisted structures may be obtained preferentially even if less crowded isomers are also feasible. It has been shown that, against all expectation, even a strong steric hindrance has no marked effect on regioselectivity and highly twisted polycyclic aromatic hydrocarbons are sometimes preferentially formed, whereas their flat and more symmetrical isomers are only obtained in minority. Highly twisted structures such as hexabenzotriphenylene (HBTP) may then be obtained very easily from flexible polyphenylene precursors.After discovering this unexpected regioselectivity, we used it on purpose to form polyhelicenic species. Attempts to prepared hexaphenanthrotriphenylene (HPTP) were unsuccessful due to reactivity issues when synthesizing the corresponding flexible precursors. By using a new versatile strategy leading to an advanced common precursor, several C3-symmetrical flexible substrates have been synthesized and submitted to Scholl reaction. The expected [6]helicenes were not obtained and rearranged products were formed instead, but TMS-bearing HBTP could be prepared, as well as a hexabenzocoronene (HBC) which exceptionnal solubility is due to the distortion of the aromatic core under the effect of bulky tert-butyl substituents in bay regions.The easily formed [5]helicene fragment has been incorporated in the design of twisted carbon nanoribbons that would be composed of a succession of such motifs. As a test reaction, the corresponding monomer and dimer have been synthesized with an excellent yield and fully characterized. Their X-ray structures have even been determined, giving interesting information about their configuration. A more general strategy has then been developed and optimized for the systematic synthesis of longer oligomers of twisted nanoribbons. Using this technique, the trimer and tetramer have been synthesized and characterized by mass spectrometry.

Nous avons proposé d'étudier le potentiel de l'outil d'épitaxie HVPE (Hydride Vapour Phase Epitaxy) pour la croissance de nanofils de GaAs. La morphologie nanofil permet au matériau épitaxié de libérer les contraintes dans le cas de l’hétéroépitaxie et de mettre en œuvre des procédés de croissance sur des substrats à faible coût comme les substrats de silicium. Dans ce contexte, j’ai effectué la croissance auto-catalysée de nanofils et des nanoobjets de GaAs par HVPE sur substrat silicium. La HVPE utilise des molécules de GaCl synthétisées à l'intérieur du réacteur dans la zone en amont du substrat à haute température (T> 700 °C). La décomposition du GaCl est beaucoup plus difficile entre 600 °C et 700 °C. Dans ce manuscrit des calculs thermodynamiques des constantes d’équilibre de formation du gallium liquide sont donnés et analysés. Les rapports de flux atomiques III/V obtenus sont de 11 à 222, bien plus élevés que les rapports utilisés dans procédés MBE et MOVPE. Ce travail expérimental a été couplé à un travail de modélisation théorique. Une étude de la faisabilité d’utiliser un substrat constitué de nanofils de GaAs comme électrode dans une pile microbienne a également été initiée. / III-V semiconductor nanowires exhibit excellent electrical and optical properties in laterally confined geometry which is very promising for monolithic integration of photonic nanodevices on silicon substrates. Hydride Vapor Phase Epitaxy (HVPE) process growth was therefore developed in this thesis for the growth of GaAs nanowires. This report is organized into two chapters.The first chapter introduces the state-of-the-art of self-catalyzed GaAs nanowires and nano-structures on silicon substrate. We have demonstrated the growth of self - catalyzed GaAs nanowires by HVPE on un-patterned Si (111) substrates at a low temperature of 600 °C with extremely high GaCl/AsH3 flow ratios. A model that explains well the experimental findings was developed. The second part proposes the design of a Microbial Fuel Cell (MFC) prototype based on GaAs nanowire samples. A MFC prototype based on GaAs nanowire and substrate was developed.

Orientador: Ronaldo Aloise Pilli / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-08T04:04:52Z (GMT). No. of bitstreams: 1 Robello_LuisGustavo_D.pdf: 7203530 bytes, checksum: a92a57231d7587b04ebb16da51b52419 (MD5) Previous issue date: 2006 / Doutorado / Quimica Organica / Doutor em Ciências

Le cancer de l’ovaire représente la quatrième cause de décès par cancer chez la femme. En France, près de 4 500 nouveaux cas par an sont diagnostiqués, avec plus de 3000 décès chaque année. Ce cancer reste longtemps silencieux : un diagnostic souvent tardif, et le développent d’une chimiorésistance qui touche jusqu'à 75 % des patientes, expliquent le fort taux de mortalité et une survie à 5 ans estimée à moins de 45 %. Les mécanismes responsables du développement de la chimiorésistance sont nombreux. Aujourd’hui, un fort intérêt est porté au développement de nouvelles stratégies de traitement en ciblant les protéines cellulaires inhibitrices de l’apoptose (mort cellulaire programmée). Deux familles de protéines jouent un rôle cruciale dans la régulation de l’apoptose : la famille Bcl-2 et la famille IAP. Nous nous sommes intéressés à la synthèse de petites molécules abiotiques, appelées foldamères. Ces composés sont capables de perturber les interactions entre les protéines anti-apoptotiques des familles Bcl-2 ou IAP, surexprimées dans le cancer de l’ovaire, et leurs partenaires biologiques (pro-apoptotiques). Ceci permet de libérer les protéines pro-apoptotiques et rétablir l’apoptose dans les cellules cancéreuses. Ce travail de thèse a permis la conception, la synthèse, la caractérisation et l’évaluation biologique de molécules inhibitrices des protéines anti-apoptotiques Mcl-1 et Bcl-xL de la famille Bcl-2, et de possibles inhibiteurs de la protéine XIAP de la famille IAP. / Ovarian cancer is the 4th leading cause of cancer death in women. In France, nearly 4,500 new cases per year are diagnosed, with more than 3,000 deaths each year. This cancer remains silent for a long time: late diagnosis and chemoresistance development for up to 75% of patients, explain the high mortality rate and the 5-year survival estimated at less than 45%. Mechanisms responsible for the development of drug resistance are numerous. Today, there is a strong interest in the development of new treatment strategies by targeting cellular proteins that inhibit apoptosis (programmed cell death). Two families of proteins play a crucial role in the regulation of apoptosis: the Bcl-2 family and the IAP family. We are interested in the synthesis of small abiotic molecules, called foldamers. These compounds are able to disrupting the interactions between the anti-apoptotic proteins of the Bcl-2 or IAP families, overexpressed in ovarian cancer, and their biological (pro-apoptotic) partners. This releases the pro-apoptotic proteins and restores apoptosis in the ovarian cancer cells. This PhD work allowed the design, synthesis, characterization and biological evaluation of inhibitors of Mcl-1 and Bcl-xL anti-apoptotic proteins of Bcl-2 family, and the development of possible inhibitors of the XIAP protein of IAP family.