manno- versus gluco-Selectivity in reductions of 2-keto-β-d-arabino-hexopyranosides

Tri-sec-butylborohydrides (L- or K-Selectride) reduce the carbonyl group in acylated 2-keto-β-d-arabino-hexopyranosides to β-d-mannosides in an essentially stereospecific fashion, whereas borane reduction gives the 2-epimeric β-d-glucosides with high preference. As preparative yields are in the 70–85% range, the ulosyl donor approach can thus be utilized for the straightforward construction of oligosaccharides containing either β-d-Man or β-d-Glc units.