Regioselective Monoalkylation of Non-protected Glycopyranosides by the Dibutyltin Oxide Method

Abstract

Regioselective monoalkylation of some pento- and hexopyranosides (Me β-L-Ara, Ph α-L-Ara, Me α-D-Xyl, Me β-D-Xyl, Me α-D-Glc, Me β-D-Glc, Me α-D-Gal, Me β-D-Gal, and Me α-D-Man) was examined by using the dibutyltin oxide method without protecting the hydroxyl groups. By this method, alkylation proceeds more or less in the same fashion as reported for acylation (through the formation of cyclic tin intermediates) and selectively activates an equatorial hydroxyl group which has an oxygenated function (OH or OMe) in a cis relationship at an adjacent position, even in the presence of a more reactive primary hydroxyl group. However, in some instances the position of activation is different. Various monoalkyl others thus prepared were identified by analyses of their carbon-13 nuclear magnetic resonance spectra.