A general and diastereoselective synthesis of 1,2-cis-hexofuranosides from1,2-trans-thiofuranosyl donors

The general formation of 1,2-trans-thioglycofuranosides derived from D-gala ctose, D-glucose and D-mannose was readily accomplished starting from the c orresponding alkyl glycofuranosides via per-O-acetyl-hexofuranoses as key s ynthons. Glycosidation of ethyl or phenyl perbenzylated 1,2-trans-thiofuran osides afforded disaccharides containing a nonreducing 1,2-cis-hexofuranosy l unit, i.e, alpha-D-galactosyl, alpha-D-glucosyl or beta-D-mannosyl, with interesting diastereoselectivities. Activation of the thiofuranosyl donors was performed by N-iodosuccinimide and a catalytic amount of tin(II) triflu oromethanesulfonate.