Anomeric Thioglycosides Give Different Anomeric Product Distributions under NIS/TfOH Activation.

The reaction of a series of anomeric thioglycosides with various glycosyl acceptors and N-iodosuccinimide/catalytic triflic acid was investigated with respect to reactivity and anomeric selectivity. In general, ß-configured donors were found to give a more ß-selective reaction outcome compared to their α-configured counterparts. The relative reactivity of various thioglycosides was measured through competition experiments, and the following order was established: phenyl, tolyl, methyl, ethyl, isopropyl, and 1-adamantyl.

α-Selective Glucosylation Can Be Achieved with 6-O-para-Nitrobenzoyl Protection.

A systematic study of the effect of various 6-O-acyl groups on anomeric selectivity in glucosylations with thioglycoside donors was conducted. All eight different esters were found to induce moderate-to-high α-selectivity in glucosylation with l-menthol with the best being 6-O-p-nitrobenzoyl. The effect appears to be general across various glucosyl acceptors, glucosyl donor types, and modes of activation. No evidence was found in favor of distal participation.