Catalytic Generation and C–C Bond Forming Reactions of Dicoordinated Carbocations
This dissertation describes the development of Lewis acid-based methodology togenerate dicoordinated carbocations catalytically. These reactive intermediates were once sparingly accessible synthetically and were mostly the focus of theoretical studies. This dissertation highlights new, mild conditions that can generate these species in a kinetically persistent fashion through the use of weakly coordinating anions in non-polar media. These conditions also enable new carbon–carbon bond forming reactions of these intermediates to take place; either through Friedel-Crafts or C–H insertion. Additionally mechanistic nuances and the key advantages and disadvantages of each developed system will be highlighted. Overall, this work features the development of this chemistry from a fundamental study to a more broadly applicable reaction. Chapter One is a brief overview of the current state of research on aryl and vinyl cations. This chapter serves as a prelude to the remaining chapters and will be referenced throughout this dissertation. Strategies to generate these reactive species, specifically ones that inspired our own research in this area are presented. Furthermore, some reactivity of these cations is also highlighted, again focusing on mechanistically similar reactions to our own. Chapter Two describes our efforts in the development of a silylium-carborane catalyzed reaction to generate aryl and vinyl cations catalytically from aryl fluorides and vinyl triflates respectively. These species were then able to be engaged in intermolecular reactions with inert C–H bonds of both alkanes and arenes resulting in a mild C–H functionalization reaction. Chapter Three discusses our investigations of lithium-based Lewis acids to generate reaction vinyl cations under highly basic conditions and their ensuing reactivity. Notably, this work also overcomes some of the challenges presented in chapter Two with regards to the functional group compatibility of these systems. This work represents an important advancement of our chemistry towards a more robust, practical reaction. Chapter Four highlights an ongoing effort in our research group to utilize different vinyl sulfonate precursors in order to access a broader class of vinyl cation intermediates. With these precursors in hand, we utilize similar conditions to Chapter Three to develop some new vinyl cation reactivity. These reactions involve trapping of vinyl cations with allylsilanes, silyl ketene acetals, and methyl ethers. Chapter Five discusses our ongoing effort to develop a “field guide” for the practicing organic chemist in order to disseminate some of our groups in-house knowledge in developing these cation methodologies over the past few years. Here, mechanistic nuances, substrate design, and choice of catalytic system are discussed.