학술논문
Applications of the Hofmann-Löffler reaction for C-H functionalization in Total Synthesis
Document Type
Dissertation/Thesis
Source
TDX (Tesis Doctorals en Xarxa)
Subject
Language
English
Abstract
Esta tesis doctoral representa algunos avances en el campo de la funcionalización de enlace C-H alifáticos. Es necesario el desarrollo de nuevos métodos para la funcionalización selectiva en moléculas orgánicas. Para llevar a cabo estas estrategias, los radicales de nitrógeno parecen perfectos candidatos para generar selectivamente enlaces de C-X en posiciones no activadas. Estos radicales de nitrógeno han sido usados como intermedios reactivos en química sintética en las últimas decadas, llevando a cabo la química de transferencia de átomos de hidrógeno, donde la conocida reacción de Hofmann-Löffler fue pionera. El primer Proyecto esta basado en el concepto de reacción de Hofmann interrumpida para la halogenación selectiva de moléculas orgánicas. Para ello, empleamos sulfonamidas y esteres de sulfamatos como grupos dirigentes de procesos de 1.5 y 1,6 de transferencia de átomos de hidrógeno para generar radicales centrados en carbono en posiciones γ or δ. Estos radicales son atrapados por átomos de halógenos dando acceso a compuestos orgánicos con múltiples halógenos en su estructura como estructuras cíclicas y acíclicas. En algunos casos, halogenacion vecinal o geminal fue observada. La segunda y tercera parte de la tesis esta relacionada con el uso de la reacción de Hofmann-Löffler para la formación del anillo de pirrolidina en alcaloides. La combinación de yodo hipervalente con cantidad catalítica de yodo pareció ser una buena estrategia para la aminación en la última etapa de la síntesis enantioselectiva de la nicotina. Por último, en la tercera parte de la Tesis demostramos que esta metodología podría aplicarse a moléculas más complejas pudiendo sintetizar la estructura del hasubanan de forma enantioselectiva donde la formación de pirrolidina se produce en los últimos pasos de la síntesis.
This doctoral Thesis summarizes advances in the field of C-H functionalization of aliphatic bonds. Methods for remote functionalization are necessary to expand the transformations available in the organic molecules. For this transformation, nitrogen-centered radicals are the perfect candidates to promote selective C-X bond formation over unactivated and distal C-H bonds. Nitrogen-centered radicals have been widely used as reactive intermediates in synthetic chemistry in the last decades, carrying out hydrogen atom transfer chemistry, where the well-known Hofmann-Löffler reaction was pioneering. The first research project is based on the concept of ‘interrupted Hofmann-Löffler’ reaction to the selective halogenation of organic molecules. For that, we employed sulfonamides or sulfamates esters as directing/protecting group of the transformation. These directing groups promote 1,5 or 1,6-hydrogen atom transfer generating the carbon-centered radical at γ or δ-positions. This radical is trapped by the addition of a halogen atom at this position. This protocol provided access to multiple halogenated organic compounds, such as cyclic and acyclic structures. In some cases, vicinal and geminal halogenation is observed. The second and the third part of my doctoral Thesis is related to the application of the Hofmann-Löffler reaction for the formation of the pyrrolidine ring into some alkaloids. The combination of hypervalent iodine(III) species with catalytic amount of molecular iodine seemed to be a robust tool for late-stage amination in the enantioselective synthesis of nicotine. In this regard, in the last part of the Thesis we demonstrated that this methodology could be applied to more complex molecules being able to synthesize the enantioselective hasubanan core where the pyrrolidine formation occurred in the last steps of the synthesis.
This doctoral Thesis summarizes advances in the field of C-H functionalization of aliphatic bonds. Methods for remote functionalization are necessary to expand the transformations available in the organic molecules. For this transformation, nitrogen-centered radicals are the perfect candidates to promote selective C-X bond formation over unactivated and distal C-H bonds. Nitrogen-centered radicals have been widely used as reactive intermediates in synthetic chemistry in the last decades, carrying out hydrogen atom transfer chemistry, where the well-known Hofmann-Löffler reaction was pioneering. The first research project is based on the concept of ‘interrupted Hofmann-Löffler’ reaction to the selective halogenation of organic molecules. For that, we employed sulfonamides or sulfamates esters as directing/protecting group of the transformation. These directing groups promote 1,5 or 1,6-hydrogen atom transfer generating the carbon-centered radical at γ or δ-positions. This radical is trapped by the addition of a halogen atom at this position. This protocol provided access to multiple halogenated organic compounds, such as cyclic and acyclic structures. In some cases, vicinal and geminal halogenation is observed. The second and the third part of my doctoral Thesis is related to the application of the Hofmann-Löffler reaction for the formation of the pyrrolidine ring into some alkaloids. The combination of hypervalent iodine(III) species with catalytic amount of molecular iodine seemed to be a robust tool for late-stage amination in the enantioselective synthesis of nicotine. In this regard, in the last part of the Thesis we demonstrated that this methodology could be applied to more complex molecules being able to synthesize the enantioselective hasubanan core where the pyrrolidine formation occurred in the last steps of the synthesis.