Stereocontrolled Routes to Functionalized C-Glycopyranosides

Article abstract of DOI:10.1021/jo00177a027

4,6-O-Ethylidene-D-glucopyranose (1) reacts with an acid-washed, stabilized Wittig reagent to give the trans-oct-2-enoate 2 in excellent yield.Cyclization is effected by treatment with dilute base, and after 1 h, a 1:1 mixture of anomers exists which is the optimum concentration of the α-D form.Continuing base treatment for 5 h leads to the β-D anomer exclusively. α-D-C-Glycopyranosides can be obtained as predominant products by Lewis acid catalyzed condensation of acetylated glycals with siloxyalkenes, and anomerization to the β-D forms can be effected with potassium tert-butoxide.For a given pair of these anomers, 1H or 13C NMR pa rameters can be used for assigning configuration α or β.