A New and Stereoselective Glycosylation and Synthesis of Origosuccaride

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Stereoselective glycosylation of 2-O-benzoyl-3,4,6-tri-O-benzyl-β-D-glucosyl fluoride with several glycosyl acceptors is successfully carried out by using a catalytic amount of trifluoromethanesulfonic acid (TfOH).A catalytic and stereoselective glycosylation of several glycosyl acceptors with β-glycosyl fluoride is successfully performed by using a catalytic amount of trityl tetrakis(pentafluorophenyl)borate [TrB(C_6F_5)_4] or TfOH.When TrB(C_6F_5)_4 was used as a catalyst, the glycosylation proceeded smoothly to afford the glycosides in high yields with high β-stereselectivities in pivalonitrile-trifluoromethylbenzene (BTF) 1 : 5 mixed solvent. Further, the glycosylation reaction of armed-disarmed strategy with this catalyst was established. Similarly, TfOH, a strong protic acid, catalyzed glycosylation afforded the corresponding β-glycosides in good to excellent yields on treating β-glycosyl fluorides having 2-O-benzoyl group with various glycosyl acceptors including thioglycosides.Glycosylation of the "armed" thioglycoside with various glycosyl acceptors is promoted by using a combination of stoichiometoric amount of N-(ethylthio)phthalimide (PhthNSEt) and catalytic amount of TrB(C_6F_5)_4, and is successfully applied to one-pot "armed-disarmed" sequential synthesis of trisaccharides.Stereoselective glycosylation of several glycosyl acceptors with 2,3,4,6-tetra-O-benzyl-β-D-glucopyranosyl fluoride was successfully carried out in diethylether by using a catalytic amount of TfOH in the coexistence of molecular sieve 5Å (MS5Å) to afford predominantly the corresponding α-linked disaccharides in high yields, which was applied to one-pot sequential syntheses of trisaccharides.