Concerning the Origin of the High β-Selectivity of Glycosidation Reactions of 2-Deoxy-2-iodo-glucopyranosyl Trichloroacetimidates

[structure: see text] Studies on the glycosidation reactions of conformationally constrained glycosyl imidates 8a and 8b were performed to evaluate the possible involvement of "conformationally inverted" oxonium ion intermediates in glycosidation reactions with 2-deoxy-2-iodo-glucopyranosyl donors. The mechanistic implications of this study are discussed, and intermediates 23 and 24 are invoked to rationalize the observed beta-selectivities.