Exploring the Far Side of Glycosyl Sulfoxide Activation Process

Comprehensive Summary The discovery of Kahne glycosylation forwards a big step in the carbohydrate chemistry. Despite an extensive series of studies, the precise mechanism of this powerful glycosylation is still not fully understood. To address these 30‐year puzzles, the far side of Kahne glycosylation is explored in this study. After a series of control and tracking experiments, a number of important intermediates including glycosyl oxo‐sulfonium ion and sulfenic anhydride (Crich's intermediate) are suggested to be responsible for the complex reaction pathway. It also reveals that in addition to the conventional ionic glycosylation pathway, a novel free radical pathway is very likely to contribute to the various side‐and co‐products. This study provides further understanding of Kahne glycosylation, and it also sheds light on how to improve the efficiency of sulfoxide‐based glycosylation reactions.