2,3,6-Tri-O-benzoyl-α-D-glucopyranosyl bromide: syntheses, methanolyses, and attempted self-condensations

Abstract

2,3,6,-Tri-O-benzoyl-α-D-glucopyranosyl bromide (I) has been prepared from 1,2,3,6-tetra-O-benzoyl-D-glucopyranose (IV) by two different methods of bromination. The bromide (I) was identified by conversion into the known methyl 2,3,6-tri-O-benzoyl-β-D-glucopyranoside. Solvolyses in methanol–dioxan (9 : 1 v/v) showed (I) to be more reactive than either 2,3,4,6-tetra-O-benzoyl-α-D-glucopyranosyl bromide (II) or 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide (III). The order of reactivity was (I) > (II) > (III)(ca. 15 : 3 : 1 at 40°). For all three halides, the corresponding O-acylated methyl β-D-glucopyranoside was the predominant product; only 1–5% of the α-anomer was formed. Attempts to condense (I) to give β-1,4-cellodextrins were unsuccessful. The reactivity of the bromine in (I) is not a factor in its failure to polymerize; the negative results are mainly attributed to the unavailability of the C(4)-hydroxy-group for reaction.