Thioglycosylation of 1,2-cis-glycosyl acetates: a long-standing overlooked issue in preparative carbohydrate chemistry

1,2-cis-Glycosyl acetates with the α-configuration were revealed to be very unreactive towards Lewis acid catalyzed thioglycosylations. Optimal and cost-effective conditions for enabling this direct conversion is absent in the literature. Our studies have shown that elevating the reaction temperature with a catalytic amount of BF3·OEt2 was more effective than changing Lewis acids with higher acidities to accommodate the low reactivity of α-glycosyl acetates. The effect of impurities in stored BF3·OEt2 on the reaction is also discussed.