Synthesis of Structurally Diverse Molecular Scaffolds Enabled by Protected Oxyallyl Cations

This dissertation focuses on the synthesis of diverse molecular scaffolds through the use of protected oxyallyl cation intermediates. Chapter One provides background on the generation and applications of oxyallyl and silyloxyallyl cations, while focusing on the direct nucleophilic capture of theses intermediates to generate functionalized ketones and silylenolates. Chapter Two depicts our approach to generate six-membered silyloxyallyl cations through the use of mild Brønsted acid activation. Regioselective nucleophilic capture of these intermediates successfully produced diverse a,a’-substituted silylenol ethers enabled by polar solvent and residual water.Chapter three details strategies to generate 1,4-dicarbonyl compounds, focusing on the capture of cationic intermediates with enolate nucleophiles. Further implementation of previously observed solvent effects in the generation of silyloxyallyl cations allowed for a mild protocol for the regioselective synthesis of 1,4-monosilylated dicarbonyl compounds via silylenolate nucleophiles. Our synthesis of 1,4-monosilylated dicarbonyls was further applied in Chapter Four to generate tetrahydroindoles and tetrahydrocyclopenta[b]pyrroles in a one-pot, three-component approach utilizing silyloxyallyl cations, silylenolate nucleophiles, and primary amines. This Brønsted acid catalyzed formal [2+2+1] annulation reaction allowed for the assembly and functionalization of nitrogen containing heterocycles in a highly modular mannerLastly, Chapter Five details a novel approach for the synthesis of α,α’-bis-quaternary ketones through an unprecedented copper catalyzed Claisen rearrangement. Regioselective nucleophilic capture of unsymmetrical disubstituted oxyallyl cations was enabled by a Lewis acidic, copper catalyst. A subsequent diastereoselective Claisen rearrangement resulted in highly functionalized α,α’-bis-quaternary ketones in moderate to excellent yields.