Based on the combined use of dimethyl-A C H T U N G T R E N N U N G formamide (DMF) modulation and neighboring group participation, three iterative one-pot a-glycosylation methods, i.e., one-pot (a,a)-, one-pot (b,a)-, and one-pot (a,b)-glycosylations, were developed. These methods are applicable to a range of thioglycosyl donors, confer stereocontrol in a-/b-glycosidic bond formation, and thus provide for rapid access to oligosaccharides with various permutations of anomeric configurations. The utility of these one-pot glycosylation methods is demonstrated in the synthesis of eight non-natural and natural oligosaccharide targets, including the core 1 serine conjugate, core 8