Bent Bond/Antiperiplanar Hypothesis: Modulating the Reactivity and the Selectivity in the Glycosylation of Bicyclic Pyranoside Models.

Glycosylation reactions were performed on a series of bicyclic C-substituted pyranoside models to isolate and analyze factors that control the glycosylation stereoselectivities observed in carbohydrates. The bent bond/antiperiplanar hypothesis (BBAH) orbital model rationalizes all of these results by considering hyperconjugation interactions between groups at C and the two τ bonds (bent bonds) of oxocarbenium ion intermediates formed under the glycosylation conditions. According to the BBAH, nucleophiles add to oxocarbenium intermediates by S2-like antiperiplanar displacement of the weaker of their two τ bonds.