Stereoselective synthesis of α-glucosides by neighbouring group participation via an intermediate thiophenium ion

The use of a 2-O-(thiophen-2-yl)methyl protecting group allows highly stereoselective α-glucosylation of a trichloroacetimidate donor; increased stereoselectivity, presumably arising from the intramolecular formation of a transient intermediate thiophenium ion, correlates with increased bulk of the glycosyl acceptor.

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3,4,6-Tri-O-benzyl-2-O-(thiophen-2-ylmethyl)-β-d-glucopyranosyl fluorideC32H33FO5SEe = 100%[α]D25=+9.7 (c 1.0 in CHCl3)Source of chirality: d-glucose

Phenyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-β-d-glucopyranosideC35H36O6SEe = 100%[α]D23=+9.4 (c 1.1 in CHCl3)Source of chirality: d-glucose

Phenyl 3,4,6-tri-O-benzyl-1-thio-β-d-glucopyranosideC33H34O5SEe = 100%[α]D23=-9.7 (c 1.0 in CHCl3)Source of chirality: d-glucose

Phenyl 3,4,6-tri-O-benzyl-2-(thiophen-2-ylmethyl)-thio-β-d-glucopyranosideC38H38O5S2Ee = 100%[α]D25=-2.0 (c 1.05 in CHCl3)Source of chirality: d-glucose