How do Various Reaction Parameters Influence Anomeric Selectivity in Chemical Glycosylation with Thioglycosides and NIS/TfOH Activation?

The reaction of glycosyl donor phenyl 2,3,4,6‐tetra‐O‐benzyl‐1‐thio‐β‐D‐glucopyranoside with NIS/TfOH(cat.) was systematically studied under various reaction conditions. Neither the molecular sieve pore size nor amount of NIS activator was found to have an effect on the α/β‐ratio in the reaction with L‐menthol as glycosyl acceptor. Increasing concentration and the amount of triflic acid catalyst, however was found to increase the β‐selectivity in certain cases. Moreover, lowering temperature was found to have a strong effect on the glycosylation outcome. [ABSTRACT FROM AUTHOR]