Part 1 : Lanthanum Triflate-Catalyzed Cyclopropanation via Intramolecular Methylene Transfer. Part 2

This thesis describes the development of novel synthetic methods in the areas of methylene transfer cyclopropanation and reaction design with aromatic cations. The first chapter presents a new cyclopropanation method involving intramolecular methylene transfer from an epoxide to an olefin. The lanthanum(III) triflate-catalyzed process proceeds with high stereoselectivity and a range of examples are presented to illustrate the reaction scope. An asymmetric cyclopropane synthesis combining enantioselective epoxidation and the methylene transfer protocol is also presented. The second chapter describes the application of aromatic cation activation for nucleophilic acyl substitution. The strategy is used to rapidly convert carboxylic acids to their corresponding acid chlorides with dichlorocyclopropene reagents. The effect of cyclopropene substituents and amine base additives on the rate of conversion is examined. A mild amidation protocol employing acid chloride formation is described and applied to acid-sensitive substrates and preparative peptide couplings. The final chapter discloses the development of aromatic cation photoredox catalysts. Investigations into the relationship between cyclopropenium substitution and ultraviolet/visible light absorption are presented. Cyclopropenium ions are shown to be effective photocatalysts for a variety of photoredox transformation.