Base-catalysed equilibration and conformational analysis of some methyl 2,3- and 3,4-anhydro-6-deoxy-β-D-hexopyranosides

Methyl 2,3-anhydro-6-deoxy-ß-D-mannopyranoside (6) and methyl 3,4-anhydro-6-deoxy-ß-D-altropyranoside (8) have been prepared from methyl 3,4-di-O-acetyl-6-deoxy-2-O-toluene-p-sulphonyl-ß-D-glucopyranoside (5). At equilibrium, in alkaline solution, the anhydromannoside is preferred by 2:1. Methyl 3,4-anhydro-6-deoxy-ß-D-galactopyranoside (14) and methyl 2,3-anhydro-6-deoxy-ß-D-gulopyranoside (16) have been prepared by the action of base on methyl 2,3-di-O-acetyl-6-deoxy-4-O-toluene-p-sulphonyl-ß-D-glucopyranoside (13) and also from methyl 2-O-acetyl-6-deoxy-3-O-toluene-p-sulphonyl-ß-D-galactopyranoside (25). At equilibrium, the anhydrogalactoside preponderates in the ratio 9:1. Nuclear magnetic resonance spectroscopy has been employed to define the conformations of the anhydro compounds and hence to rationalise the results of the base-catalysed equilibrations. © 1974.