The use of 2-O-alkoxymethyl groups as effective stereodirecting substituents for the construction of 1,2-trans glycosidic linkages is reported. The observed stereoselectivity arises from the intramolecular formation of a five-membered cyclic architecture between the 2-O-alkoxymethyl substituent and the oxocarbenium ion, which provides the expected facial selectivity. Furthermore, the observed stereocontrol and the extremely high reactivity of 2-O-alkoxymethyl-protected donors allowed development of a one-pot sequential glycosylation strategy that should become a powerful tool for the assembly of oligosaccharides.
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