Stereoselective O-Glycosylation of Glycals with Arylboronic Acids Using Air as the Oxygen Source

An open-air palladium-catalyzed O-glycosylation was developed using glycals and arylboronic acids with base additives at ambient conditions. The novel approach enabled facile access to various O-glycosides in high yields, with exclusive 1,4-cis-stereoselectivity tolerating reactive hydroxyl/amino groups. Mechanistic studies indicated that chemo-/stereoselectivity arose from the coordination between palladium and phenols generated in situ by oxidizing arylboronic acids, followed by an intramolecular attack. Isotope-labeling experiments revealed that the oxygen of O-glycosidic bonds came from O2.