Highly reactive 2-deoxy-2-iodo-d- allo and d- gulo pyranosyl sulfoxide donors ensure β-stereoselective glycosylations with steroidal aglycones.

The preparation of well-defined d- xylo and d- ribo glycosides represents a synthetic challenge due to the limited configurational availability of starting materials and the laborious synthesis of homogeneous 2-deoxy-β-glycosidic linkages, in particular that of the sugar-steroid motif, which represents the "stereoselective determining step" of the overall synthesis. Herein we describe the use of 2-deoxy-2-iodo-glycopyranosyl sulfoxides accessible from widely available d-xylose and d-ribose monosaccharides as privileged glycosyl donors that permit activation at very low temperature. This ensures a precise kinetic control for a complete 1,2- trans stereoselective glycosylation of particularly challenging steroidal aglycones.