Thio-click reaction of 2-deoxy-exo-glycals towards new glycomimetics: stereoselective synthesis of C-2-deoxy-D-glycopyranosyl compounds
A series of 2-deoxy-glycopyranosyl cyanides with D-arabino, D-lyxo, D-erythro, and D-threo configurations was synthesized from the corresponding glycals via 2-deoxy-glycopyranosyl acetates. The cyanides were transformed to anhydro-aldose tosylhydrazones by reduction with NaH2PO2/Ra-Ni in the presence of tosylhydrazine. The tosylhydrazones furnished 2-deoxy-exo-glycals under modified Bamford–Stevens conditions. Photoinitiated thiol–ene additions of these exo-glycals resulted in the corresponding C-(2-deoxy-D-glycopyranosyl)methyl sulfides in medium to good yields with exclusive regio- and stereoselectivities in most cases. Several disaccharide mimics with a C–S moiety in place of the glycosidic oxygen were also obtained.