New Synthetic Methods and Reagents for Complex Carbohydrates. VIII. Stereoselective<i>α</i>- and<i>β</i>-Mannopyranoside Formation from Glycosyl Dimethylphosphinothioates with the C-2 Axial Benzyloxyl Group
The reactions of mannopyranosyl dimethylphosphinothioates and alcohols using silverperchlorate as an activator in the presence of molecular sieves 4A in benzene at room temperature gave the 1,2-trans-α-mannopyranosides in good yields. On the other hand, 1,2-cis-β-mannopyranosides could be obtained from the dimethylphosphinothioates by the combined use of iodine and 5 mol% triphenylmethyl perchlorate