Indium(III) bromide-mediated β-selective thioglycosylation of 1,2,4-O-orthoacetylglucose derivatives

1,2,4-O-Orthoacetyl-α-d-glucose possesses a skew-boat glucopyranose ring whose steric strain is expected to show high reactivity. This study describes the β-selective thioglycosylation of 1,2,4-O-orthoacetyl-α-d-glucose. Indium(III) bromide catalyzes the reaction in trifluoromethylbenzene at ambient temperature in the presence of molecular sieves 4A, resulting in the corresponding thioglycoside product with perfect β-selectivity and high yields. The presented glycosylation might be useful for the synthesis of functional molecules and natural products possessing sugar moieties.