Prearranged glycosides. Part 14: Intramolecular glycosylation of non-symmetrically tethered glycosides

Partially benzylated 1-thio-β-d-glucopyranosides were tethered via position 2 to position 3 of methyl α-d-glucopyranosyl and benzyl 2-phthalimido-2-deoxy-β-d-glucopyranosyl derivatives, respectively, by non-symmetrical o-, m-, and p-methylbenzoate linkers. Intramolecular glycosylation of these prearranged glycosides lead to the corresponding non-symmetrically tethered α-(1→4)-linked disaccharides as the exclusive or main products. The tethers were regioselectively opened by transesterification affording isomeric disaccharide acceptors which are susceptible for further elongation of the sugar chain at positions 3 and 2′, respectively.