A General and Diastereoselective Synthesis of 1,2-cis-Hexofuranosides from 1,2-trans-Thiofuranosyl Donors

The general formation of 1,2-trans-thioglycofuranosides derived from D-galactose, D-glucose and D-mannose was readily accomplished starting from the corresponding alkyl glycofuranosides via per-O-acetyl-hexofuranoses as key synthons. Glycosidation of ethyl or phenyl perbenzylated 1,2-trans-thiofuranosides afforded disaccharides containing a nonreducing 1,2-cis-hexofuranosyl unit, i.e. α-D-galactosyl, α-D-glucosyl or β-D-mannosyl, with interesting diastereoselectivities. Activation of the thiofuranosyl donors was performed by N-iodosuccinimide and a catalytic amount of tin(II) trifluoromethanesulfonate.