Benzoylated ethyl 1-thioglycosides: direct preparation from per-O-benzoylated sugars

d-Glucose, lactose, maltose, and melibiose were benzoylated with Bz2O–Et3N reagent to give fully benzoylated β products. Under the same conditions, d-mannose produced a mixture where the β-benzoate predominated. Treatment of the foregoing compounds with EtSH at slightly elevated temperature (50–60 °C) in the presence of BF3·Et2O as a promoter gave the corresponding ethyl 1-thio glycosides in high yields. The α-products predominated in all cases in the anomeric mixtures formed. Individual products of all reactions were isolated by chromatography, they were obtained in analytically pure state, and were fully characterized by 1H and 13C NMR data and physical constants.

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► Benzoylation of unprotected sugars with Bz2O–Et3N gives benzoylated β products.
► Treatment of benzoylated sugars with EtSH–BF3·Et2O gives ethyl 1-thioglycosides.
► Anomeric mixtures of 1-thioglycosides are formed from α or β benzoates.