2-Nitro-thioglycosides: α- and β-Selective Generation and Their Potential as β-Selective Glycosyl Donors

Michael-type addition of thiolates to 2-nitro-D-glucal or to 2-nitro-D-galactal derivatives readily provides 2-deoxy-2-nitro-1-thioglycosides. Kinetic and thermodynamic reaction control permitted formation of either the alpha- or preferentially the beta-anomers, respectively. Addition of achiral and chiral thiourea derivatives to the reaction mixture increased the reaction rate; the outcome is substrate-controlled. The 2-deoxy-2-nitro-1-thioglycosides are excellent glycosyl donors under arylsulfenyl chloride/silver triflate (ArSCl/AgOTf) activation, and they provide, anchimerically assisted by the nitro group, mostly beta-glycosides.