Analysis of the factors that govern stereoselectivity in the reactions of oxocarbenium ion intermediates: The role of neighboring-group participation and the correlation between nucleophile strength and stereoselectivity

The chemical synthesis of oligosaccharides and natural products containing carbohydrate moieties is often hampered by the inability to form glycosidic linkages in a stereoselective manner. This dissertation discusses investigations into the factors that control stereoselectivity in additions to endocyclic oxocarbenium ion intermediates and related model systems. Chapter one focuses on the role of neighboring-group participation by sulfur substituents. Spectroscopic evidence for the formation of low energy sulfonium ion intermediates is discussed, as are data indicating that nucleophilic addition occurs through higher energy oxocarbenium ion intermediates. Chapter two details the correlation between nucleophilicity and stereoselectivity in the reactions of alcohol nucleophiles and oxocarbenium ion intermediates. The erosion of selectivity with increasing reactivity is consistent with rates of nucleophilic addition that approach the diffusion limit. Chapter three discusses the extension of the diffusion limit hypothesis to reactions of allyl Grignard reagents and carbonyl compounds.