Publication: Desarrollo de nuevos procesos de ciclación
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2017-06-26
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Universidad Complutense de Madrid
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Abstract
Las reacciones de cicloadición y ciclación constituyen una de las herramientas más ampliamente empleada en síntesis debido a su capacidad para aumentar la complejidad molecular en una única etapa sintética.1 En esta tesis doctoral se desarrollan y estudian nuevos procesos de cicloadición y ciclación con sustratos cuyas características estructurales y electrónicas les confieren las propiedades idóneas para su empleo en este tipo de reacciones: ciclopropanos dador-aceptor (D-A) y complejos metal-carbeno de tipo Fischer. Objetivos y Resultados Capítulo 1: El empleo de ciclopropanos D-A para la síntesis directa de anillos carbo- y heterocíclicos mediante reacciones de ciclación [3+2], [3+3] o [4+3] se ha estudiado ampliamente.2 Sin embargo, el uso de estos ciclopropanos D-A en reacciones de ciclación de alto orden ha sido muy poco explorado.3 Por ello, el primer objetivo de este capítulo es estudiar la reacción de cicloadición [8+3] entre ciclopropanos D-A y derivados de tropona. Esta transformación, catalizada por SnCl4, da lugar a derivados de tetrahidrociclohepta[b]piranos con completa regio- y diasteroselectividad (Esquema 1). De acuerdo a cálculos computacionales, esta reacción transcurre por pasos a través de un intermedio zwitteriónico a partir del cual se produce el cierre del anillo, etapa que controla la regio- y diastereoselectividad del proceso, dando lugar a los correspondientes cicloaductos [8+3]...
Cycloaddition reactions are highly valuable transformations in modern organic synthesis because of their ability to increase the molecular complexity in a single synthetic step.1 The aim of this dissertation is to develop and study new cyclisation processes using substrates whose structural and electronic properties makes them the ideal candidates to be used in these reactions, namely donor-acceptor cyclopropanes and Fischer type carbene complexes. Goals and Results Chapter 1: Donor-acceptor cyclopropanes (DACs) have proven to be very useful for the direct synthesis of carbo- and heterocycles via [3+2]-, [3+3]- or [4+3]- cycloaddition reactions.2 Nevertheless, the use of DACs in high-order cycloaddition reactions has been scarcely explored.3 Therefore, the first goal of the chapter is the study of the [8+3] cycloaddition reaction between DACs and tropone derivatives. This high-order SnCl4-catalysed cycloaddition reaction leads to the formation of amino-substituted tetrahydrocyclohepta[b]pyrans in good reaction yields and with complete regio- and diastereoselectivities (Scheme 1). By means of computational- DFT methods, it was found that this transformation proceeds stepwise through a zwitterionic intermediate. From this intermediate a ring closure step, which controls the regio- and diastereoselectivities, occurs to produce the observed [8+3]- cycloadducts...
Cycloaddition reactions are highly valuable transformations in modern organic synthesis because of their ability to increase the molecular complexity in a single synthetic step.1 The aim of this dissertation is to develop and study new cyclisation processes using substrates whose structural and electronic properties makes them the ideal candidates to be used in these reactions, namely donor-acceptor cyclopropanes and Fischer type carbene complexes. Goals and Results Chapter 1: Donor-acceptor cyclopropanes (DACs) have proven to be very useful for the direct synthesis of carbo- and heterocycles via [3+2]-, [3+3]- or [4+3]- cycloaddition reactions.2 Nevertheless, the use of DACs in high-order cycloaddition reactions has been scarcely explored.3 Therefore, the first goal of the chapter is the study of the [8+3] cycloaddition reaction between DACs and tropone derivatives. This high-order SnCl4-catalysed cycloaddition reaction leads to the formation of amino-substituted tetrahydrocyclohepta[b]pyrans in good reaction yields and with complete regio- and diastereoselectivities (Scheme 1). By means of computational- DFT methods, it was found that this transformation proceeds stepwise through a zwitterionic intermediate. From this intermediate a ring closure step, which controls the regio- and diastereoselectivities, occurs to produce the observed [8+3]- cycloadducts...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Químicas, Departamento de Química Orgánica, leída el 22/06/2016