On the regioselectivity of the Hanessian-Hullar reaction in 4,6-O-benzylidene protected galactopyranosides

Carbohydrate Research
David CrichAlbert A Bowers

Abstract

The N-bromosuccinimide mediated fragmentation of methyl 4,6-O-benzylidene-beta-D-galactopyranoside results in the formation of methyl 4-O-benzoyl-6-bromo-6-deoxy-beta-D-galactopyranoside and methyl 4-O-benzoyl-3-bromo-3-deoxy-beta-D-gulopyranoside, as opposed to the methyl 6-O-benzoyl-3-bromo-3-deoxy-beta-D-gulopyranoside originally reported. The kinetic methyl 4-O-benzoyl-6-bromo-6-deoxy-beta-D-galactopyranoside rearranges to the thermodynamic methyl 4-O-benzoyl-3-bromo-3-deoxy-beta-D-gulopyranoside under the reaction conditions, likely via a 3,6-anhydro galactopyranoside. The NBS-mediated cleavage of 4,6-O-benzylidene acetals in the galactopyranoside series is therefore shown to conform to the regiochemistry observed in the corresponding gluco- and mannopyranoside series with preferential cleavage of the C6-O6 bond by an ionic mechanism.

Citations

Apr 22, 2010·Proteins·Kresten Lindorff-LarsenDavid E Shaw
Jul 25, 2012·Chemical Communications : Chem Comm·Jian ZhangBiao Yu
Dec 14, 2018·The Journal of Organic Chemistry·Satsawat VisansirikulAlexei V Demchenko
Jun 6, 2018·Chemical Reviews·Suvarn S KulkarniShang-Cheng Hung

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