Determination of the absolute configuration of sulfinyl glycosides: the role of the exo-anomeric effect

The diastereoselective synthesis and conformational study of α- and β-ethylsulfinylglycosides have been studied. It was found that while β-(SS)-sulfinyl glycosides are flexible β-(RS)-sulfinyl glycosides exists in a major conformation stabilized by the exo-anomeric effect. The generality of the hyperconjugative delocalisation gives rise to a general rule for the determination of the absolute configuration of sulfinyl glycosides by 1H or 13C NMR spectroscopy without need of chemical shift reagents.