The photochemistry of a variety of tetrahydro-1,4-naphthoquinones (structure 1) has been investigated. These were synthesized by Diels-Alder reaction of corresponding p-quinones and acyclic-1,3-dienes [diagram omitted]. Three substituent-dependent types of reactions were observed: (1) for adducts possessing hydrogen substituents at C₄a and C₈a (bridgehead position), the prevalent process was one of abstraction of a β-hydrogen atom from C₅(or equivalently, C₈) by excited carbonyl oxygen. In general, three product types were then observed, derived from carbon-carbon bond formation (proceeded in two instances by conformational rotation about the C₄a - C₈a bond) in the bisallylic radical so produced. Placing a methyl or phenyl substituent at C₂ renders the β-hydrogens non-equivalent, and abstraction occurs in accord with expectations based on the formation of the more stable biradical intermediate. In adducts possessing bridgehead substituents, rotation about the C₄a - C₈a bond in the biradical is suppressed and only a single product type (enone alcohol) is formed, which possesses the same relative conformation as the biradical and starting adduct. In the case where the bridgehead substituents are carboxymethyl, however, secondary photolysis in benzene solution occurs, giving rise to a product where the bridgehead substituents are nearly eclipsed. (2) For the adduct possessing exo-methyl substituents at positions 5 and 8 as well as methyls at the bridgehead positions and at and C₂ and C₃, hydrogen abstraction was partially suppressed in favor of a process tentatively concluded to involve Ύ~hydrogen abstraction by excited enone carbon, giving rise to a product, the formation of which again requires little conformational change in the biradical. (3) For adducts possessing endo-methyl substituents at C₅ and C₈ as well as bridgehead substituents, a novel oxetane product was observed, formally the result of a cycloaddition reaction involving the remote double bond and one of the carbonyl groups. The oxetane derived from the duroquinone adduct was found to be photolabile, giving back starting material and, eventually, a quantitative conversion to a novel cage diketone. The reactivity differences for these systems, as well as for those previously studied in our laboratory, are interpreted as being due to the effects of substituents on the energy barrier to conformational isomerization in the biradical intermediates. Finally, the potential utility of these photochemical reactions for the synthesis of unusual ring systems is noted. / Science, Faculty of / Chemistry, Department of / Graduate

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Thermally induced retro-Diels Alder (rDA) reaction has been extensively used for the preparation of many reactive intermediates in organic synthesis. But the uses of photo-retro Diels-Alder (PrDA) reaction in organic synthesis were sparingly reported in literature. Due to its spatial and temporal control, PrDA can be used in making of photosensitive materials, in drug delivery and also for mechanistic studies. Diels-Alder adducts of tetracyanoethylene (TCNE) and polyaromatic compounds (anthracene, napthacene, pentacene and phencyclone) were synthesized and were subjected to PrDA reaction through 254-nm irradiation. The quantum yield and the consequent photoreactivity of these DA adducts follow the following order. TCNE/naphthacene greater than] TCNE/anthracene greater than or equal to] TCNE/pentacene This trend was explained by a mechanism of charge-separated intermediates. The stability of the charge-separated intermediate is the governing factor of this trend of photoractivity of DA adducts. Based on these results it is possible to design a proper DA adduct and consequently predict the feasibility of the PrDA reaction.

No description available.

Esta tese apresenta as reações entre o aduto de Diels-Alder 2,3-diclorobenzoquinona-ciclopentadieno e alguns nucleófilos, não descritas na literatura, conforme pode ser verificado pela revisão bibliográfica apresentada no primeiro capítulo. Assim, dezenove novos adutos dialquiltio- e diariltio-substituídos, bem como o correspondente difenilseleno derivado, foram sintetizados e caracterizados. As reações com alguns nucleófilos de oxigênio e nitrogênio falharam, fornecendo o aduto diclorado aromatizado. O aduto dimetiltio-substituído aromatizado foi obtido pela reação do aduto diclorado com excesso de metil mercapteto do sódio. Algumas reações dos adutos ditio-substituídos foram investigadas, tais como a de retro Diels-Alder, fotociclizacao e oxidação. A reação de retro Diels-Alder permitiu a síntese de três novas benzoquinonas 2,3-dialquiltio-substituídas, as quais foram identificados e caracterizadas. No caso da 2,3-dimetiltio benzoquinona, a sua reação com ciclopentadieno forneceu o aduto dimetiltio-substituído, que se mostrou idêntico àquele obtido a partir do aduto diclorado. As experiências de fotociclização com alguns adutos dialquiltio-substituídos não conduziram aos compostos \"gaiola esperados. Algumas experiências de oxidação do aduto dimetiltio substituído são descritas, bem como a síntese do aduto metiltiometilsulfinil-substituído. Este não sofreu posterior oxidação, nem ciclizou sob irradiação. Contudo, sua reação com cloreto de tionila foi bem sucedida, pois conduziu ao aduto cloro-alquiltio substituído, o qual não pode ser sintetizado diretamente pela reação entre quantidades equimolares do aduto diclorado e mercapteto. Os mecanismos destas reações são discutidos, apontando - se a importância do aduto cloro-alquiltio-substituído como intermediário em síntese de adutos mistos ditio-substituídos. Apesar desta inesperada falta de reatividade na fotociclização, os adutos ditio-substituídos mostraram possuir configuração endo, conforme foi demonstrado por evidências químicas e de espectroscopia de13C. As possíveis causas desta falta de reatividade, até agora não registrada na literatura em outros adutos endo, são discutidas. / This thesis presents reactions not yet described in the literature between the 2,3-dichlorobenzoquinone-cyclopentadiene Diels-Alder adduct and some nucleophiles, as shown by a bibliographic survey, initially presented. Thus, nineteen new dialkylthio and diarylthiobenzoquinones-cyclopentadiene adducts and the corresponding diphenylseleno one were synthesized. The reactions with some oxygen and nitrogen nucleophiles failed and afforded the aromatized dichloro adduct. The aromatized dimethylthio-substituted adduct was obtained by the reaction of the dichloro adduct with an excess of sodium methyl mercaptide. Some reactions of the dithio-substituted adducts were investigated, such as the retro Diels-Alder, photocyclization and oxidation. The retro Diels-Alder reaction led to the synthesis of three new 2,3-dialkylthiobenzoquinones, which were identified and characterized. The 2,3-dimethylthiobenzoquinone underwent Diels-Alder reaction with cyclopentadiene to give the dimethylthio- substituted adduct which showed to be identical to that obtained from the dichloro adduct. The irradiation of some dialkylthio- substituted adducts did not afford the expected \"cage\" compounds. Some oxidation experiments with the dimethylthio-substituted adduct are described, and the synthesis of the methylthio- methylsulphinyl-substituted adduct is reported. The latter did not undergo further oxidation nor cyclization on irradiation. However, successful reaction was obtained with thionyl chloride, leading to the chloro-alkylthio-substituted adduct which could not be synthesized by reaction between dichloro adduct and mercaptide in 1:1 proportion. The mechanisms for both reactions are discussed and the possibility of the chloro-alkylthio-substituted adduct being an intermediate for the synthesis of the mixed dithio-substituted adducts is suggested. Despite of the lack of reactivity on photocyclization the dithio-substituted adducts were shown to be endo by chemical and 13C spectroscopics evidences. Possible factors which would be responsible for this unusual inertness for the endo adducts, are discussed.

Nosso grupo de pesquisa já vem há alguns anos estudando métodos para a síntese do núcleo estrutural dos furanoeliangolidos, mais especificamente do goiazensolido. A estrutura básica deste composto corresponde a um sistema 7-oxabiciclo [6.2.1] undecano, e ele possui atividades biológicas como esquistossomicida, citotóxica e antiinflamatória. Em nosso trabalho utilizamos como etapa chave a reação de Diels-Alder, que é geralmente eficiente e rápida para formação de sistemas policíclicos. Na ultima etapa da proposta sintética, propomos a clivagem da ligação interna do sistema policíclico para obtenção do macrociclo desejado. / Our research group has been studying, for some years, new methods for the synthesis of the core structure of the furanoheliangolides, more specifically of goyazensolide. The basic structure of this compound is a 7-oxabicyclo [6.2.1] undecane system, and it shows biological activities such as schistosomicidal, cytotoxic and anti-inflammatory. In this work, we have used the Diels-Alder reaction as a key step, since it is usually fast and efficient for the synthesis of polycyclic structures. As a last step, we proposed that the cleavage of the internal bond of the rings should furnish the desired macrocycle.

Nosso grupo de pesquisa já vem há alguns anos estudando métodos para a síntese do núcleo estrutural dos furanoeliangolidos, mais especificamente do goiazensolido. A estrutura básica deste composto corresponde a um sistema 7-oxabiciclo [6.2.1] undecano, e ele possui atividades biológicas como esquistossomicida, citotóxica e antiinflamatória. Em nosso trabalho utilizamos como etapa chave a reação de Diels-Alder, que é geralmente eficiente e rápida para formação de sistemas policíclicos. Na ultima etapa da proposta sintética, propomos a clivagem da ligação interna do sistema policíclico para obtenção do macrociclo desejado. / Our research group has been studying, for some years, new methods for the synthesis of the core structure of the furanoheliangolides, more specifically of goyazensolide. The basic structure of this compound is a 7-oxabicyclo [6.2.1] undecane system, and it shows biological activities such as schistosomicidal, cytotoxic and anti-inflammatory. In this work, we have used the Diels-Alder reaction as a key step, since it is usually fast and efficient for the synthesis of polycyclic structures. As a last step, we proposed that the cleavage of the internal bond of the rings should furnish the desired macrocycle.

Esta tese apresenta as reações entre o aduto de Diels-Alder 2,3-diclorobenzoquinona-ciclopentadieno e alguns nucleófilos, não descritas na literatura, conforme pode ser verificado pela revisão bibliográfica apresentada no primeiro capítulo. Assim, dezenove novos adutos dialquiltio- e diariltio-substituídos, bem como o correspondente difenilseleno derivado, foram sintetizados e caracterizados. As reações com alguns nucleófilos de oxigênio e nitrogênio falharam, fornecendo o aduto diclorado aromatizado. O aduto dimetiltio-substituído aromatizado foi obtido pela reação do aduto diclorado com excesso de metil mercapteto do sódio. Algumas reações dos adutos ditio-substituídos foram investigadas, tais como a de retro Diels-Alder, fotociclizacao e oxidação. A reação de retro Diels-Alder permitiu a síntese de três novas benzoquinonas 2,3-dialquiltio-substituídas, as quais foram identificados e caracterizadas. No caso da 2,3-dimetiltio benzoquinona, a sua reação com ciclopentadieno forneceu o aduto dimetiltio-substituído, que se mostrou idêntico àquele obtido a partir do aduto diclorado. As experiências de fotociclização com alguns adutos dialquiltio-substituídos não conduziram aos compostos \"gaiola esperados. Algumas experiências de oxidação do aduto dimetiltio substituído são descritas, bem como a síntese do aduto metiltiometilsulfinil-substituído. Este não sofreu posterior oxidação, nem ciclizou sob irradiação. Contudo, sua reação com cloreto de tionila foi bem sucedida, pois conduziu ao aduto cloro-alquiltio substituído, o qual não pode ser sintetizado diretamente pela reação entre quantidades equimolares do aduto diclorado e mercapteto. Os mecanismos destas reações são discutidos, apontando - se a importância do aduto cloro-alquiltio-substituído como intermediário em síntese de adutos mistos ditio-substituídos. Apesar desta inesperada falta de reatividade na fotociclização, os adutos ditio-substituídos mostraram possuir configuração endo, conforme foi demonstrado por evidências químicas e de espectroscopia de13C. As possíveis causas desta falta de reatividade, até agora não registrada na literatura em outros adutos endo, são discutidas. / This thesis presents reactions not yet described in the literature between the 2,3-dichlorobenzoquinone-cyclopentadiene Diels-Alder adduct and some nucleophiles, as shown by a bibliographic survey, initially presented. Thus, nineteen new dialkylthio and diarylthiobenzoquinones-cyclopentadiene adducts and the corresponding diphenylseleno one were synthesized. The reactions with some oxygen and nitrogen nucleophiles failed and afforded the aromatized dichloro adduct. The aromatized dimethylthio-substituted adduct was obtained by the reaction of the dichloro adduct with an excess of sodium methyl mercaptide. Some reactions of the dithio-substituted adducts were investigated, such as the retro Diels-Alder, photocyclization and oxidation. The retro Diels-Alder reaction led to the synthesis of three new 2,3-dialkylthiobenzoquinones, which were identified and characterized. The 2,3-dimethylthiobenzoquinone underwent Diels-Alder reaction with cyclopentadiene to give the dimethylthio- substituted adduct which showed to be identical to that obtained from the dichloro adduct. The irradiation of some dialkylthio- substituted adducts did not afford the expected \"cage\" compounds. Some oxidation experiments with the dimethylthio-substituted adduct are described, and the synthesis of the methylthio- methylsulphinyl-substituted adduct is reported. The latter did not undergo further oxidation nor cyclization on irradiation. However, successful reaction was obtained with thionyl chloride, leading to the chloro-alkylthio-substituted adduct which could not be synthesized by reaction between dichloro adduct and mercaptide in 1:1 proportion. The mechanisms for both reactions are discussed and the possibility of the chloro-alkylthio-substituted adduct being an intermediate for the synthesis of the mixed dithio-substituted adducts is suggested. Despite of the lack of reactivity on photocyclization the dithio-substituted adducts were shown to be endo by chemical and 13C spectroscopics evidences. Possible factors which would be responsible for this unusual inertness for the endo adducts, are discussed.