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Bent Bond/Antiperiplanar Hypothesis: Modulating the Reactivity and the Selectivity in the Glycosylation of Bicyclic
Jean-François Parent1, Ghislain Deslongchamps2, Pierre Deslongchamps1
1Département de Chimie, Université Laval, Québec, QC G1V 0A6, Canada.
Abstract:
Glycosylation reactions were performed on a series of bicyclic C2-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 C2 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 SN2-like antiperiplanar displacement of the weaker of their two τ bonds.
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