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Master's Dissertation
DOI
https://doi.org/10.11606/D.46.2019.tde-09032020-100502
Document
Author
Full name
Ronaldo Cesar da Silva
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2019
Supervisor
Committee
Marzorati, Liliana (President)
Albuquerque, Cristina Northfleet de
Vinhato, Elisângela
Title in Portuguese
Estudo sobre a preparação de isoquinuclidinas a partir de sais de piridínio
Keywords in Portuguese
Isoquinuclidinas
Oxazolidinas
Sais de piridínio
Abstract in Portuguese
Quando os sais tetrafluoroborato de N-metil-2,4,6-trifenil-piridínio (1a) e tetrafluoroborato de N-metil-2,4-difenil-6-terc-butil-piridínio (1b) foram submetidos à reação aldólica com dois aldeídos aromáticos, na presença de hidróxido de sódio aquoso, na concentração de 10% (m/v), em lugar dos aldois esperados, formaram-se oxazolidinas, pelo ataque do oxigênio às posições adjacentes ao átomo de nitrogênio do anel heterocíclico. Em ambos os casos foram obtidas duas oxazolidinas isoméricas e, para o sal 1b, observou-se completa regiosseletividade, a favor do ataque ao carbono do anel heterocíclico substituído pelo grupo fenila. O procedimento para a preparação das oxazolidinas foi otimizado, passando-se a utilizar um sistema líquido/líquido (diclorometano/água) e, como catalisador de transferência de fase, o brometo de hexadecil-trimetilamônio. As reações aldólicas produziram as oxazolidinas derivadas do sal 1a e do p-cloro ou m-clorobenzaldeídos, em cerca de 60% de conversão. Estas oxazolidinas instáveis que não puderam ser isoladas, mas que foram utilizadas diretamente na reação de Diels-Alder com o dienófilo N-metilmaleimida. Os adutos formados foram isolados por cromatografia de coluna em sílica e a análise estrutural, realizada por experimentos de RMN de H, indicou que se tratavam das formas isomerizadas dos adutos originais. Nestes novos adutos, o anel oxazolidínico está voltado para a dupla ligação do biciclo. A reação aldólica do sal 1a com um aldeído contendo um centro estereogênico (aldeído de Garner) produziu em uma mistura de oxazolidinas isoméricas. O produto bruto desta reação foi submetido à cicloadição com Nmetilmaleimida, resultando um produto, isolado por cromatografia em coluna de sílica, cujos dados espectroscópicos sugerem trata-se de uma isoquinuclidina sob a forma de dois rotâmeros.
Title in English
Studies on the preparation of Isoquinuclidines from Pyridinium salts
Keywords in English
Isoquinuclidines
Oxazolidines
Pyridinium salts
Abstract in English
Two pyridinium salts, namely N-methyl-2,4,6-triphenylpyridinium (1a) and N-methyl- 2,4-diphenyl-6-tert-butylpyrdinium (1b) tetrafluoroborates were submitted to aldol addition to two aromatic aldehydes, in the presence of aqueous sodium hydroxide (10% w/v). In lieu of the expected aldol products, oxazolidines were formed, as a result of the nucleophilic attack of the aldolate to the heterocyclic ring. Such products were unstable and could not be isolated by usual purification methods. Improved conversion (60%) could be achieved under phase transfer conditions, using as catalyst the hexadecyltrimethyl ammonium bromide. Some diastereoselectivity was observed for the aldol addition of salt 1a to p-clorobenzaldehyde (3:1). As for 1b, although complete regioselectivity could be observed in the analogous aldol addition, the diastereomeric oxazolidines were formed in equal amounts. However after some time, the diateromeric ratio changed substancially. The cycloadiition of oxazolidines, derived from p-chloro or m-chlorobenzaldehyde, and using N-methylmaleimide as dienophile, yielded the corresponding isoquinuclidines that were isolated by column chromatography. However, using such purification method, the original adducts were isomerized to new isoquinuclidines, bearing the oxazolidine ring syn to the bicycle double bond. In order to try to prepare optically active isoquinuclidines, the aldol reaction was performed with 1a and an aldehyde bearing a stereo defined center (Garner aldehyde). Purification by column chromatography on silica allowed for the isolation of a single product. Spectral data point to an isoquinuclidine structure, but full interpretation was precluded by the presence of rotamers.
 
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Publishing Date
2020-08-07
 
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