A Catalytic Koenigs-Knorr Glycosylation Based On Acceptor Activation With In（NTf₂）₃

Glycosides are a class of important compounds widely existing in nature.They participate in many physiological processes of life and their biological activities show diversity.Synthetic access to ample O-glycosidically linked carbohydrate units is often necessary to gain better insight in their involvement into biologically significant processes.Chemical glycosylation is a common strategy for glycosidic-bond formation.The Koenigs-Knorr reaction provides an attractive pathway to glycosides because aldosyl halides are a useful category of building blocks.An efficient glycosylation protocol has been developed that employs indium-promoted Koenigs-Knorr reaction with In（NTf₂）₃ at catalytic loadings.The reactions proceeded smoothly at room temperature to afford a variety of glycosides in the satisfactory yield and with the good stereoselectivity.No additive is required,which is an important feature of this method.Finally,mechanistic investigations suggest that the reaction proceeds via the formation of an alkoxy-indium adduct that displays enhanced oxygen-centered nucleophilicity relative to a free alcohol.