Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-Graduação em Química. / Made available in DSpace on 2012-10-21T10:53:02Z (GMT). No. of bitstreams: 1 205083.pdf: 997838 bytes, checksum: 69b41bfe4864b07c72e1cb147ddb8f73 (MD5) / Os compostos 2-(2-bromoetoxi)-3-alquilfenóis (alquil = metil, isopropil, sec-butil e terc-butil) foram sintetizados a partir do catecol, do 3-metilcatecol e de 3-alquilcatecóis, obtidos a partir de 2-alquilfenóis apropriados, por estratégias de transformação da hidroxila em um poderoso grupo orto diretor de metalações e orto-litiação, seguida de boração e oxidação. Os 2-(2-bromoetoxi)-3-alquilfenóis foram imediatamente ciclizados para 5-alquil-1,4-benzodioxanos pela adição de uma solução alcalina. As constantes de velocidade de primeira ordem e os parâmetros de ativação foram determinados para a formação de 5-alquil-1,4-benzodioxanos a partir de 2-(2-bromoetoxi)-3-alquilfenóis sintetizados. A introdução de um grupo alquílico linear na posição 3 do anel aromático causa um aumento de velocidade de ca 5 vezes na reação de ciclização, mas a substituição por um grupo terc-butil resulta em um fator de aumento de ca 43 vezes. Os parâmetros de ativação para a série estudada mostra uma pequena variação no ?H? (79,19 para 83,97 kJ/mol). O incremento de velocidade tem o ?S? como termo principal, que aumenta com a complexidade do grupo alquílico, sendo +12,36 J/K.mol para o 2-(2-bromoetoxi)fenol e +31,42 J/K.mol para o 2-(2-bromoetoxi)-3-terc-butilfenol. Os valores de molaridade efetiva para a série indicam a influência do efeito da restrição conformacional causada pela substituição alquílica nos fatores de incremento de velocidade relatados. Cálculos de modelagem molecular sustentam o mecanismo via substituição nucleofílica intramolecular e as mesmas tendências de variação nas energias de ativação.

Metal-catalyzed cyclopropanation of olefins with diazo reagents is one of the most general and efficient method to prepare cyclopropanes. The resulting cyclopropyl units are found as a basic structural element in a wide range of naturally occurring compounds and biologically active compounds, and can serve as versatile synthetic intermediates in the synthesis of multifunctionalized cycloalkanes and acyclic compounds. Since Co(II) complexes of D2-symmetric chiral amidoporphyrins [Co(D2-Por*)] were first introduced in 2004, Co(II)-metalloradical catalysis (MRC) have emerged as a new platform for asymmetric cyclopropanation. These metalloradical catalysts have been shown to be highly effective for asymmetric intermolecular cyclopropanation of a broad scope of substrates with different diazo reagents, with excellent diastereoselectivity and enantioselectivity. This dissertation aims to develop new Co(II)-MRC based enantioselective cyclopropanation systems. It will elaborate on three types of stereoselective cyclopropanation reactions from olefins: radical cyclopropanation with α-halodiazoacetates, asymmetric bicyclization of diazoketones, and radical cyclopropanation with fluoroaryl diazomethanes. These three processes will be examined in the context of diastereo- and enantiocontrol. And also, the application of cyclopropanation products have been demonstrated, which could potentially lead to more exciting works.

<p> It has been shown that the hydroxy compounds la-4a possess triplet states which are substantially shorter-lived than those of their methoxy analogs (lb-4b). In each case the efficient quenching of the excited carbonyl triplet state has been attributed to intramolecular phenolic hydrogen abstraction. Evidence for this is found in the detection of biradical species generated from triplet decay, primary hydrogen-deuterium kinetic isotope effects and thermodynamic parameters which support both atom transfer (enthalpy) and high degrees of order (entropy) in the transition state necessary for the proposed abstraction process. The difference in triplet lifetimes (16 ns to 1135 ns) is due almost exclusively to varying degrees of difficulty in obtaining a transition state geometry in which the phenoxy hydrogen is properly lined up for intramolecular hydrogen abstraction. </p> / Thesis / Master of Science (MSc)

No description available.

No presente trabalho foram investigados vários sistemas moleculares contemplando um ou mais grupos NO2 com características fortemente elétron atraentes, e por outro lado um grupo fortemente elétron doador (NH2, OH ou N3H) conectados através de um anel benzênico ou piridínico. A caracterização das propriedades de transferência de carga intramolecular (CT) nesses sistemas constitui um dos principais objetivos do trabalho, tendo sido para tanto utilizadas as técnicas de espectroscopia eletrônica, espectroscopia vibracional (Raman e infravermelho) e com grande destaque, a espectroscopia Raman ressonante. Essa investigação permitiu a caracterização dos grupos cromofóricos envolvidos na CT entre os vários substituintes e suas posições relativas. Em vários casos foi possível estender a investigação para as espécies aniônicas obtidas pela desprotonação dos grupos NH2, OH e N3H, quando então se nota mudança abrupta das características da transição de transferência de carga (energia e intensidade), o que por sua vez conduz a uma muito maior deslocalização eletrônica do cromóforo, como revelado pela análise dos espectros de absorção (UV-Vis) e Raman ressonante (RR). No caso de sistemas mais estendidos, como é o caso típico do ânion do 1,3-bis(4-nitrofenil)triazeno os dados de espectroscopia eletrônica e espectroscopia Raman ressonante mostram de maneira clara a presença de duas transições de transferência de carga na região do visível, o que caracteriza um sistema bicromofórico. / In the present work were investigated molecular systems bearing one or more NO2 groups, with strong electron withdrawing characteristics, in addition to a strong electron donating group (NH2, OH, N3H), connected to a benzene or pyridine ring. The characterization of the intramolecular charge transfer (CT) process in such systems is one of the main objects of this work and for such, electronic spectroscopy, vibrational spectroscopy (Raman and IR) and in special, resonance Raman spectroscopy were used. The study revealed the chromophoric moieties involved in the CT transitions in the several molecules investigated, included the ones where the relative positions of the substituents were changed. In several cases it was possible to extend the study to the anionic species that results from the deprotonation of the NH2, OH and N3H groups, where an abrupt change of the CT transition (energy and intensity) is observed, and what in its turn leads to a much more delocalized chromophore, as revealed by the UV-Vis and resonance Raman spectra. In the case of the more extended systems, as in the typical case of 1,3-bis(4-nitropheyl)triazene anion, the data show clearly the presence of two CT transitions in the visible region, what amounts to the formation of a bichromophoric system.

Intramolecular energy transfer is reviewed from several perspectives, such as the generally accepted mechanism and molecular structure dependence. Some unique molecules with bichromophores or trichromophores linked by rigid bridges were designed to serve as models for studying the intramolecular triplet-triplet energy transfer. Bichromophoric molecules containing an anthracene donor and phenanthrene or diphenylpolyene acceptors linked by linearly fused norbornane units were synthesized. Approaches to the analogous compounds with anthracene as the donor and benzophenone or p-terphenyl as acceptors are presented. Synthetic approaches to cis, exo-1, 4-dihydro-1, 4-methanotriphenylene, a precursor to the polynorbornyl-linked polychromophore, and trichromophoric compounds linked by adamantane spacers were explored.

Diss. (sammanfattning) Stockholm : Karol. inst., 2003. / Härtill 5 uppsatser.

Diss. (sammanfattning) Stockholm : Karol. inst., 2006. / Härtill 4 uppsatser.

No presente trabalho foram investigados vários sistemas moleculares contemplando um ou mais grupos NO2 com características fortemente elétron atraentes, e por outro lado um grupo fortemente elétron doador (NH2, OH ou N3H) conectados através de um anel benzênico ou piridínico. A caracterização das propriedades de transferência de carga intramolecular (CT) nesses sistemas constitui um dos principais objetivos do trabalho, tendo sido para tanto utilizadas as técnicas de espectroscopia eletrônica, espectroscopia vibracional (Raman e infravermelho) e com grande destaque, a espectroscopia Raman ressonante. Essa investigação permitiu a caracterização dos grupos cromofóricos envolvidos na CT entre os vários substituintes e suas posições relativas. Em vários casos foi possível estender a investigação para as espécies aniônicas obtidas pela desprotonação dos grupos NH2, OH e N3H, quando então se nota mudança abrupta das características da transição de transferência de carga (energia e intensidade), o que por sua vez conduz a uma muito maior deslocalização eletrônica do cromóforo, como revelado pela análise dos espectros de absorção (UV-Vis) e Raman ressonante (RR). No caso de sistemas mais estendidos, como é o caso típico do ânion do 1,3-bis(4-nitrofenil)triazeno os dados de espectroscopia eletrônica e espectroscopia Raman ressonante mostram de maneira clara a presença de duas transições de transferência de carga na região do visível, o que caracteriza um sistema bicromofórico. / In the present work were investigated molecular systems bearing one or more NO2 groups, with strong electron withdrawing characteristics, in addition to a strong electron donating group (NH2, OH, N3H), connected to a benzene or pyridine ring. The characterization of the intramolecular charge transfer (CT) process in such systems is one of the main objects of this work and for such, electronic spectroscopy, vibrational spectroscopy (Raman and IR) and in special, resonance Raman spectroscopy were used. The study revealed the chromophoric moieties involved in the CT transitions in the several molecules investigated, included the ones where the relative positions of the substituents were changed. In several cases it was possible to extend the study to the anionic species that results from the deprotonation of the NH2, OH and N3H groups, where an abrupt change of the CT transition (energy and intensity) is observed, and what in its turn leads to a much more delocalized chromophore, as revealed by the UV-Vis and resonance Raman spectra. In the case of the more extended systems, as in the typical case of 1,3-bis(4-nitropheyl)triazene anion, the data show clearly the presence of two CT transitions in the visible region, what amounts to the formation of a bichromophoric system.

This thesis describes the efforts towards the synthesis of the guaiane-6,12-olide skeleton, which characterises the guaianolide family of bioactive natural compounds. Two approaches have been investigated: the intramolecular hetero Diels Alder (IMHDA) reaction and the intramolecular carbonyl ene reaction. This thesis has been divided in three sections: the first part gives a general background about the guaianolides, the second section describes the synthetic approaches we investigated and, finally, the third section reports the experimental details. The first section gives a brief overview about the biosynthesis, the biological activities of the guaianolides, and the most interesting synthetic approaches to obtain them. The second section describes the two different approaches we investigated and gives a theoretical background about the main chemical transformations used. At first, the IMHDA reaction approach is described: a brief overview of palladium catalysis and Diels Alder reaction is given, and it is followed by the results and discussion of our study. Similarly, a theoretical background of the Alder ene reaction is given, before the results and discussion of the intramolecular carbonyl ene reaction approach are described: particular importance is given to the reasoning that led to the assignment of the relative configuration of the cycloadducts obtained, and to the rationalisation of this stereochemical outcome. Finally, the third section gives a complete description of the experimental procedures followed, and of the experimental data for the synthetic studies performed in the previous chapter.