Defining the Scope of the Acid-Catalyzed Glycosidation of Glycosyl Bromides.

Following the recent discovery that traditional silver(I) oxide-promoted glycosidations of glycosyl bromides (Koenigs-Knorr reaction) can be greatly accelerated in the presence of catalytic TMSOTf, reported herein is a dedicated study of all major aspects of this reaction. A thorough investigation of numerous silver salts and careful refinement of the reaction conditions led to an improved mechanistic understanding. This, in turn, led to a significant reduction in the amount of silver salt required for these glycosylations. The progress of this reaction can be monitored by naked eye, and the completion of the reaction can be judged by the disappearance of characteristic dark color of Ag2 O. Further evidence on higher reactivity of benzoylated α-bromides in comparison to that of their benzylated counterparts has been acquired.