Reações enantiosseletivas de aza-Wacker utilizando ligantes oxazolínicos como etapa chave para a formação de produtos naturais
Data
2023-03-10
Autores
Ariga, Elaine Miho 
Orientadores
Rodrigues, Alessandro
Tipo
Tese de doutorado
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Resumo
A reação assimétrica de aza-Wacker é uma importante ferramenta para formação de heterociclos, no qual podem fornecer produtos com altos níveis de enatiosseletividade como etapa chave para a preparação de diversos compostos mais complexos, como produtos naturais. Este estudo se iniciou objetivando-se a formação de produtos de aminoacetoxilação em altos níveis de enantiosseletividade e rendimentos, no entanto as reações testadas forneceram outro produto igualmente interessante, mas com resultados mais promissores, mudando-se a trajetória da pesquisa. A nova meta traçada foi investigar reações enantiosseletivas de aza-Wacker empregando carbamatos como materiais de partida e Pd(II) como catalisador, no qual foi observado que ligantes oxazolínicos fornecem resultados melhores frente a ligantes imidazolínicos. Foram testados carbamatos com olefinas E e Z, em que as olefinas Z forneceram resultados mais interessantes que as olefinas E, porém como esse último tem uma gama maior de substratos que podem ser utilizados como materiais de partida para obtenção do carbamato, foi realizada a otimização da reação de aza-Wacker, no qual o complexo Qox + Pd, na presença de benzoquinona como oxidante e sal quartenário de amônio como aditivo básico forneceu o melhor resultado (rendimento de 17% e excesso enantiomérico de 62%). Durante essa trajetória também foi estudada outra reação: haloaminociclização racêmica de diversos carbamatos, que foi realizado em conjunto com outra integrante do grupo.
Asymmetric aza-Wacker reaction is an important tool for organic chemistry, because these reactions can yield high enantioselectivity products. These reactions are a key step for preparations of complex molecules, such as natural product. In the first moment, this study aimed to study aminoacetoxilation of carbamates, but the results leaded to another reaction: Aza Wacker. With this new purpose, this work aimed to study asymmetric aza-Wacker reaction using carbamates, Pd(II) as catalyst and imidazolinic and oxazolinic ligands, whereupon it was observed that oxazolinic ligands yielded better results than imidazolinic ligands. It was tested olefinic carbamates E and Z and observed that olefinic Z can easily react when compared to olefinic E. In reactions using olefinic Z it was not necessary to use oxidants in the reaction to give the desired product in a good yield, when the olefinic E was used there were some difficulties to reproduce the same result. As the substrate available in the laboratory was much more accessible to provide several different olefinic carbamates E, the study proceeded using olefinic E and there was a need to optimize the aza-Wacker reaction, whereas it was found the optimized condition was: Qox + Pd(II) complex, Benzoquinone as oxidant and quaternary ammonium salt as base additive, which provided: 17% yield and e.e.: 62%. Among these reactions cited before, haloaminocyclization was also studied in a cooperation with another colleague of the Alessandro’s group, which the aim of the work was to study of formation of racemic bromoaminocyclization compounds.
Asymmetric aza-Wacker reaction is an important tool for organic chemistry, because these reactions can yield high enantioselectivity products. These reactions are a key step for preparations of complex molecules, such as natural product. In the first moment, this study aimed to study aminoacetoxilation of carbamates, but the results leaded to another reaction: Aza Wacker. With this new purpose, this work aimed to study asymmetric aza-Wacker reaction using carbamates, Pd(II) as catalyst and imidazolinic and oxazolinic ligands, whereupon it was observed that oxazolinic ligands yielded better results than imidazolinic ligands. It was tested olefinic carbamates E and Z and observed that olefinic Z can easily react when compared to olefinic E. In reactions using olefinic Z it was not necessary to use oxidants in the reaction to give the desired product in a good yield, when the olefinic E was used there were some difficulties to reproduce the same result. As the substrate available in the laboratory was much more accessible to provide several different olefinic carbamates E, the study proceeded using olefinic E and there was a need to optimize the aza-Wacker reaction, whereas it was found the optimized condition was: Qox + Pd(II) complex, Benzoquinone as oxidant and quaternary ammonium salt as base additive, which provided: 17% yield and e.e.: 62%. Among these reactions cited before, haloaminocyclization was also studied in a cooperation with another colleague of the Alessandro’s group, which the aim of the work was to study of formation of racemic bromoaminocyclization compounds.
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Reações enantiosseletivas de aza-Wacker utilizando ligantes oxazolínicos como etapa chave para a formação de produtos naturais