α-d-Glucosylation by 6-O-Acetyl-2,3,4-tri-O-benzyl-d-glucopyranose Using Trimethylsilyl Triflate and Pyridine. Synthesis of α-Maltosyl and α-Isomaltosyl α-d-Glucosides

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Abstract
The d-glucosylation of methyl 2,3,4-tri-O-benzyl-α-d-glucopyranoside and methyl 2,3,6-tri-O-benzyl-β-d-glucopyranoside by 2,3,4,6-tetra-O-benzyl-α-d-glucopyranose using pyridine and excess trimethylsilyl triflate was carried out in dichloromethane, 1,2-dimethoxyethane, and acetonitrile. In a given solvent, the selectivity of the reaction varied depending on the type of hydroxyl group of the glucosyl acceptors. The d-glucosylation of these acceptors with 6-O-acetyl-2,3,4-tri-O-benzyl-d-glucopyranose employing this reagent system in dichloromethane proceeded with good α-selectivity irrespective of the type of the hydroxyl group. This α-d-glucosylation was applied for the synthesis of O-α-d-glucopyranosyl-(1→4)- and -(1→6)-α-d-glucopyranosyl α-d-glucopyranosides from α,α-trehalose.