Synthesis of All Eight L‐Glycopyranosyl Donors Using CH Activation

Abstract

The synthesis of all eight rare, but biologically important l-hexoses as the according thioglycosyl donors was achieved through a procedure involving the CÀH activation of their corresponding 6-deoxy-l-hexoses. The key steps of the procedure were the silylation of the OH group at C4 followed by an intramolecular C À H activation of the methyl group in g-position; both steps were catalyzed by iridium. The following Fleming-Tamao oxidation and acetylation gave the suitably protected l-hexoses. This is the first general method for the preparation of all eight l-hexoses as their thioglycosyl donors ready for glycosylation and the first example of an iridiumcatalyzed C(sp 3 )ÀH activation on sulfide-containing compounds.