Elemental fluorine for selective fluorination
This thesis relates an investigation into the use of elemental fluorine in the direct and selective fluorination of organic molecules. The thesis is divided into seven chapters which may be outlined in the following manner. Chapter One. This chapter reviews the established background of the project. It discusses the historical background of direct fluorination, the preparation and properties of elemental fluorine, its use as a reagent in selective electrophilic fluorinations in organic synthesis and its use in the generation of other selective electrophilic fluorinating agents. Chapter Two. This chapter relates the development of a new methodology for the selective fluorodesulphurisation of 1,3-dithiolanes to generate diaryl geminal difluorides using elemental fluorine. It also details a new, simple deprotection procedure for these dithiolanes discovered in the course of this work. Chapters Three and Four. The third chapter details the extension of a previously established method for the direct, selective fluorination of deactivated aromatic compounds using acids as reaction solvents, particularly sulphuric and formic acids. We relate the importance of acid strength and the degree of activation of the substrate. The tolerance of the substrate to highly acidic conditions is also a key factor. Chapter Four details further investigations of the fluorination of aromatic systems, particularly more highly activated compounds. The fluorination of mesitylene or 1,3,5-trimethylbenzene, in a variety of solvents is outlined, the reaction exhibiting limited success. We contrast the chemistry of the deactivated 4-nitrotoluene and demonstrate that the presence of nitro-additives promotes the electrophilic fluorination of mesitylene. Chapter Five to Seven. Experimental details of the work discussed in Chapters Two-Four.