Zugl.: Clausthal, Techn. Univ., Diss., 2009

Thesis (M.A.)--Boise State University, 2009. / Title from t.p. of PDF file (viewed June 24, 2010). Includes bibliographical references (leaves 73-77).

Thesis (M.A.)--University of North Carolina at Greensboro, 2007. / Title from PDF title page screen. Advisor: Christopher Hodgkins, Karen L. Kilcup; submitted to the Dept. of English. Includes bibliographical references (p. 30-31, p. 64).

O objetivo deste trabalho foi investigar o uso de NbCl5 como ácido de Lewis em síntese orgânica (reações de abertura de epóxidos, reações de Diels-Alder e substituição eletrofílica de ciclo-enonas no anel furano e em reações de formação de beta-cloro-enonas e beta-etóxi-enonas a partir de beta-dicetonas e seus derivados acetilados. O comportamento de vários epóxidos quando tratados com NbCl5 foi estudado. Em geral verificou-se que os epóxidos estudados reagem rapidamente com NbCl5, levando geralmente à formação de mais de um produto (cloridrinas, 1,2-dióis, produtos contendo resíduos de solvente, como também produtos de rearranjo foram obtidos). Foi realizado um estudo detalhado verificando o efeito da temperatura (t.a., 0ºC ou -78ºC) e da concentração molar de NbCl5 nessas reações, com relação ao tempo e rendimento das reações, e à composição dos produtos. Reações entre diferentes ciclo-enonas (dienófilos de baixa reatividade) com ciclopentadieno e furanos (dienos) foram realizadas na presença de NbCl5. As reações mostraram que o NbCl5 é um bom ácido de Lewis para ativar reações de Diels-Alder ou substituição eletrofílica do hidrogênio pela ciclo-enona no anel furano. O produto de Diels-Alder foi obtido apenas na reação entre a ciclo-hexenona e o dieno mais reativo (ciclopentadieno). Dienos menos reativos, furano e 2-metil-furano levaram à formação de produtos de substituição eletrofílica do hidrogênio pela ciclo-enona no anel furano. beta-Dicetonas e seus derivados acetilados foram convenientemente transformados em beta-cloro-enonas e beta-etóxi-enonas pelo tratamento com NbCl5, em uma única etapa e em bons rendimentos. Observamos que quando as reações são realizadas em Et2O ou CH2Cl2 como solventes, apenas beta-cloro-enonas são formadas. Contudo, usando EtOAc como solvente, os resultados dependem da estrutura do substrato: substratos alfa-metilados formam exclusivamente beta-cloro-enonas (como nos outros solventes), enquanto os outros substratos levam à formação de beta-etóxi-enonas ou de misturas de beta-cloro-enonas e beta-etóxi-enonas. / The aim of this work was to investigate the use of NbCl5 as Lewis acid in organic synthesis (opening of epoxide rings, Diels-Alder and electrophilic substitution of cycloenones in furan ring reactions and in the formation of beta-chloroenones and beta-ethoxyenones from beta-diketones and the corresponding acetylated derivatives. The behaviour of several epoxides when treated with NbCl5 was studied. In general it was verified that the studied epoxides react rapidly with NbCl5, giving, in most cases, more than one product (chlorohydrins, 1,2-diols, products containing solvent residues as well as rearrangement products were obtained). A detailed study was performed to verify the effect of the temperature (rt, 0ºC or -78ºC) and of the NbCl5 molar concentration in the composition of the products, yield and time required for the reactions. Reactions between different cycloenones (dienophiles of low reactivity) with cyclopentadiene and furans (dienes) were performed in the presence of NbCl5. The reactions showed that NbCl5 is a good Lewis acid for Diels-Alder or electrophilic substitution of the hydrogen by the cycloenone system in furan ring. The Diels-Alder product was obtained only in reaction between the cyclohexenone and the highly reactive diene (cyclopentadiene). Less reactive dienes such as furan and 2-methylfuran gave electrophilic substitution of hydrogen by the cycloenone system in the furan ring. beta-Diketones and the corresponding acetylated derivatives were conveniently transformed in beta-chloroenones or beta-ethoxyenones by treatment with NbCl5, in one step and in good yields. When the reactions were carried out with Et2O or CH2Cl2 as solvents, only beta-chloroenones were obtained. However, with EtOAc as solvent, the results depend on the structure of the substrate: alpha-methylated substrates gave exclusively beta-chloroenones (as in other solvents), while the other substrates gave beta-ethoxyenones or mixtures of beta-ethoxyenones and beta-chloroenones.

No intuito de subsidiar e orientar futuras pesquisas astroquímicas pela busca de novas espécies moleculares, foram calculadas diversas propriedades em nível CCSD/cc-pVQZ (como geometrias, cargas atômicas, momentos de dipolo, frequências vibracionais e intensidades fundamentais de infravermelho) de bases de Lewis (B) presentes no meio interestelar (B = CO, CS, SO, HCN, FCN, ClCN, BrCN, HNC, FNC, ClNC, BrNC, OCS, HCNO HOCN, HONC, HNCO, NCCN e CNNC) e de suas espécies protonadas. Além disso, o modelo Carga - Fluxo de Carga - Fluxo de Dipolo (CFCFD), em termos dos multipolos da Teoria Quântica de Átomos em Moléculas (QTAIM), foi empregado para o estudo das variações nas intensidades de infravermelho de modos de estiramento durante a protonação. Os resultados indicam que, dependendo da extremidade da molécula na qual o próton se liga, há fortalecimento ou enfraquecimento das bandas de infravermelho originais. Estes fenômenos parecem estar associados à alteração de carga inicial durante a protonação, com fluxos de carga e de dipolo coordenados com tais mudanças de carga iniciais durante as vibrações. No que concerne ao estiramento da ligação formada após a protonação, [B-H]+, a contribuição de carga é preponderante quando o próton se liga aos átomos mais eletronegativos e menos polarizáveis (O, N e F). Todavia, quando o próton se liga ao par eletrônico isolado do carbono (isonitrilas, CO e CS) ou a outros átomos como cloro, bromo e enxofre, a contribuição de fluxos de carga e de dipolo atômico se tornam mais relevantes. De qualquer maneira, a raiz quadrada da intensidade de infravermelho desta nova banda de absorção correlaciona-se com a carga do próton de forma linear. No que se refere à partição da energia eletrônica por meio da aproximação de Átomos Quânticos Interagentes, verifica-se que: (1) a energia de estabilização do próton é proporcional à carga eletrônica recebida da base; (2) a desestabilização da base aumenta quanto maior a quantidade de carga eletrônica doada para o próton e (3) a energia de interação dos fragmentos é bastante específica de cada sistema, o que origina uma separação em grupos de sistemas semelhantes. / In order to support and guide future astrochemical research related to the search for new molecular species, some properties were calculated at the CCSD/cc-pVQZ level (such as geometry, atomic charges, dipole moments, vibrational frequencies and fundamental infrared intensities) for Lewis bases (B) present in the interstellar medium (B = CO, CS, SO, HCN, FCN, ClCN, BrCN, HNC, FNC, ClNC, BRNC, OCS, HCNO, HOCN, HONC, HNCO, NCCN and CNNC) and its protonated species. In addition, the Charge - Charge Flux - Dipole Flux (CCFDF) model in terms of multipoles from the Quantum Theory of Atoms in Molecules (QTAIM) was used to study the variations in the infrared intensities of stretching modes during protonation. The results indicate that there is strengthening or weakening of the original infrared bands depending on the molecule end to which the proton is attached. These phenomena appear to be associated with the initial redistribution of electronic charge during protonation, resulting in charge and dipole fluxes coordinated with such initial rearrangement during the vibrations. Moreover, regarding the stretching intensity of the bond formed after protonation, [BH]+, the charge contribution is predominant when the proton is bound to atoms more electronegative and less polarizable atoms (O, N and F). However, when the proton binds to the lone (electron) pair of carbon (isonitriles, CO and CS) or to other atoms such as chlorine, bromine and sulfur, the charge and dipole fluxes become more significant. Nevertheless, the square root of the intensity for this new infrared absorption band correlates linearly with the charge assumed by the proton. Finally, with respect to the electronic energy partition through the Interaction Quantum Atom proposal, it is seen that (1) the proton stabilization energy is proportional to the electronic charge received from the base; (2) the destabilization of the base increases in line with the amount of electronic charge lost to the proton and (3) the interaction energy between the fragments is very specific of each system, which results in group separations.

Les travaux de recherche fondamentale présentés ici sont ancrés au cœur de la chimie organique de synthèse moderne, et plus particulièrement dans le domaine de la multi-organocatalyse énantiosélective. Dans ce manuscrit, nous avons identifié deux organocascades originales et démontré la pertinence synthétique de l'une d'elle par des applications en synthèse totale de produits naturels. L’originalité de ce travail repose sur l’utilisation d’un NHC de la classe des 1,3-imidazol-2-ylidenes comme base de Brønsted ou base de Lewis organocatalytique / The basic research work presented herein is anchored at the core of modern synthetic organic chemistry, and more specifically in the field of enantioselective multi-organocatalysis. In this manuscript, we have identified two original organocascades and demonstrated the synthetic relevance of one of these through applications in total synthesis. The originality of the work lies on the use of a 1,3-imidazol-2-ylidene NHC as an organocatalytic Brønsted or Lewis base.

Ce manuscrit présente le développement de nouvelles réactivités mettant en jeu des sources d’halogène électrophile et leur application dans les réactions de carbocyclisation de substrats possédant des fonctions carbonées insaturées. Le concept d’activation par une base de Lewis de l’agent d’halogénation a été étudié dans ce type de réactions, d’abord en version racémique, puis en version énantiosélective. L’efficacité des chalcogénures de phosphines et de phosphites a en particulier été démontrée dans les réactions d’iocarbocyclisation d’énynes-1,5 et d’iodoarylation d’oléfines. De nouveaux organocatalyseurs chiraux ont par la suite été synthétisés par analogie aux bases de Lewis achirales utilisées. Des molécules chirales de types chalcogénures de phosphoramidites et de phosphites ont ainsi été préparées et leur activité a par la suite été évaluée dans la perspective du développement d’une version asymétrique des réactions d’iodocarbocyclisation étudiées précédemment. En parallèle, de nouvelles méthodologies impliquant des substrats possédant une fonction allène ont été développées. En particulier, la réaction d’iodocarbocyclisation d’arylallènes a permis d’accéder à des 2-iodoindènes polysubstitués selon un procédé 5-endo avec des rendements allant jusqu’à 95%. / This manuscrit concerns the development of new reactivities, involving electrophilic halogen sources and their application in carbocyclization reactions of substrates bearing unsaturated carbon functions. The concept of Lewis base activation of the halogenation reagent was assessed in this type of reaction, first in a racemic version, then in an enantioselective fashion. In particular, the efficiency of phosphine and phosphite chalcogenides has been demonstrated in iodocarbocyclization reactions of 1,5-enynes and iodoarylation reactions of olefins. New chiral organocatalysts were afterwards synthesized by analogy with achiral Lewis bases previously employed. Thus, chiral molecules such as phosphoramidite and phosphite chalcogenides were prepared and their activity has been evaluated in the perspective of the development of an asymmetric version of these reactions. In parallel, new methodologies involving substrates bearing an allene function were developed. In particular, the iodocarbocyclization reaction of arylallenes was exploited to access polysubstituted 2-iodoindenes following a 5-endo process with yields up to 95%.

Typescript (photocopy).

Des complexes NHC du gallium(III) et de l’indium(III) ont été préparés. Ces composés, simples à synthétiser, se sont révélés être beaucoup plus stables que les sels commerciaux de type MX₃ (M = Ga, In ; X = Cl, Br, I). Ces complexes, une fois activés par AgSbF₆, présentent un fort caractère acide de Lewis. [IPr-GaCl₂][SbF₆] s’est ainsi montré très actif en tant qu’acide de Lewis π et a été utilisé comme catalyseur dans différentes réactions impliquant l’activation de fonctions carbonées insaturées. Il a ainsi permis d’effectuer des hydroarylations inter- et intramoléculaires d’alcynes, d’alcènes et d’allènes. La généralité de cette transformation a pu être démontrée dans une réaction tandem de cycloisomérisation/Friedel-Crafts entre un arényne et un nucléophile aromatique. La capacité des complexes cationiques de gallium et d’indium à activer des alcènes a également pu être mise à profit pour la réduction de dérivés styréniques en présence de cyclohexa-1,4-diène comme source d’hydrogène. Et parce que ces complexes permettent la génération de dérivés du styrène par hydroarylation d’alcynes, une cyclisation réductrice d’arénynes sans précédent a pu être développée. Enfin le complexe [IPr-GaCl₂][SbF₆] a été utilisé dans des réaction impliquant l’eau en tant que réactif. Quelques alcynes ont ainsi pu être hydratés et des esters γ,δ-insaturés ont été transformés en lactones. En résumé, nos complexes cationiques de gallium et d’indium peuvent être utilisés dans des réactions généralement considérées comme relevant du domaine des métaux de transition nobles (Au, Pt, Ru…). / NHC complexes of gallium(III) and indium(III) have been prepared. These compounds, easy to synthesize, proved to be much more stable than the commercially-available salts MX₃ (M = Ga, In ; X = Cl, Br, I). These complexes, once activated by AgSbF₆, show a strong Lewis acid character. For instance, [IPr-GaCl₂][SbF₆] showed a high activity as π-Lewis acid and was used as catalyst in several reactions triggered by the activation of unsaturated C-C bonds such as inter- and intramolecular hydroarylations of alkynes, alkenes and allenes. The versatility of this transformation was demonstrated in a cycloisomerization/Friedel-Crafts tandem reaction between an arenyne and an aromatic nucleophile. The ability of cationic complexes of gallium and indium to activate alkenes was also used for the reduction of styrene derivatives with 1,4-cyclohexadiene as hydrogen source. Also, because these complexes are able to generate styrene derivatives by hydroarylation of alkynes, an unprecedented reductive cyclization of arenynes could be developped. Moreover, [IPr-GaCl₂][SbF₆] was used in reactions involving water as reagent. Several alkynes were hydrated and γ,δ-unsaturated esters were transformed into lactones. In summary, our cationic complexes of gallium and indium can be used in reactions generally catalyzed by noble metals (Au, Pt, Ru…).

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