Targeted synthesis of unprecedented fundamental hydrocarbons

Abstract

Fundamental hydrocarbons have played a key role in the field of organic chemistry. The study of these hydrocarbons has led to innovations and advances in understanding structure/reactivity relationships of organic molecules. Compounds with a high degree of unsaturation have often been associated with a certain level of instability which has hindered their practical preparation and utility. Advances in preparative methodology have opened new opportunities for accessing novel scaffolds, which have enabled investigations regarding their potential applications in material science. This thesis describes efforts towards the preparation and studies of pi-bond rich scaffolds that either have eluded previous synthesis or have no prior precedent in the literature. Chapter One describes synthetic efforts towards two members of the triafulvalenes, stabilized as iron tricarbonyl complexes. Chapter Two investigates a new class of exocyclic cross-conjugated hydrocarbons, trimethylenecyclopentenes. Chapter Three explores the intramolecular reactivity of templated [3]dendralenes and Chapter Four presents new insights into the reactivity of a tetracyclic diene as part of an attempt towards hexaprismane. Chapter One investigates a novel route towards two elusive members of the fulvalenes, namely triapentafulvalene and triaheptafulvalene. To date, attempts to access triapentafulvalene have so far been unsuccessful while currently there are no reported syntheses towards triaheptafulvalene, including any substituted derivatives. Previous approaches to fulvalenes have mainly focused on low-temperature reactions as these compounds are exceptionally reactive and rapidly decompose under standard laboratory conditions. Herein, we describe the attempted synthesis of triafulvalenes using an iron tricarbonyl protecting group strategy in our attempts to prepare triapentafulvalene and triaheptafulvalene. The unexpected reactivity of synthetic intermediates is described. Chapter Two describes the first synthesis of a polyalkylydenecycloalkene, namely trimethylenecyclopentene thereby opening up uncharted structural space. Metathesis reactions were successfully used to access the unsubstituted and mono-substituted compounds. Alternate routes were required in order to synthesise substituted derivatives, although limitations of these approaches were identified. The stability of both the unsubstituted and substituted compounds is briefly discussed. Chapter Three explores the chemical behavior of two [3]dendralene molecules templated to [2.2]paracyclophane rigid backbone, a previously unexplored substituted derivative of [3]dendralene. The photochemical, thermal and radical reactivity of this molecule was explored to gain insight into tethered cross-conjugated systems. Substituted derivatives were also synthesized and studies. These investigations are complementary to the known through-conjugated systems tethered to a [2.2]paracyclophane rigid backbone. Chapter Four investigates the cycloaddition reactivity profile of [4.2.2]bicyclodecatetraene, an intermediate in the proposed synthesis of hexaprismane, a currently unreported caged polycycle. Although the reactivity of [4.2.2]bicyclodecatetraene proved unsuccessful in the synthesis of hexaprismane, unusual reactivity pathway of this molecule was uncovered and explored. Show more