On the Gluco/Manno Paradox: Practical α‐Glucosylations by NIS/TfOH Activation of 4,6‐O‐Tethered Thioglucoside Donors

A practical protocol for obtaining α-glucosides was established. It was found that 4,6-O-benzylidene or 4,6-O-(di-tert-butylsilylene) tethering of glucosyl donors of the thioglycoside type enables highly α-selective glucosylation under conditions of N-iodosuccinimide (NIS)/triflic acid (TfOH) activation. The α-glucosylations were further found to be largely independent of promoter system, temperature, leaving group and anomeric configuration. The results are discussed in the context of the Glucose/Mannose paradox in glycosylation chemistry.