Investigations on Leaving Group Based Intra- versus Intermolecular Glycoside Bond Formation

Abstract

Ligation of the glycosyl donor to the glycosyl acceptor through the leaving group was performed with the aim of enforcing glycoside bond formation by an intramolecular (1.x)-shift. To this end, syntheses of alkoxymethyl (2a and b), 2-alkoxyethyl (10a and b, 13a, 16a), 3-alkoxypropenyl (27a and b), and 7-alkoxy-4-oxaheptadienyl thioglucopyranoside derivatives (35a,b and d) were carried out. Their activation with thiophilic promoter systems gave the expected glucopyranosides 5a,b and d in up to high chemical yields, yet modest anomeric control. Competition experiments showed that an intermolecular reaction course is favored in these reactions, although model considerations imply that convenient intramolecular (1,3)-, (1,4)-, (1,5)-, and (1,9)-shifts, respectively, of the glycosyl donor to the acceptor are possible.