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 α- or preferentially the β-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
β-glycosides.