Block synthesis of oligosaccharides. Part 1: Preparation of furanosyl-1-thiopyranosides

Condensation of fully benzylated pentafuranosyl dithiocarbamates 2a–c with (5-nitro-2-pyridyl) 2,3,4-tri-O-benzoyl-1-thio-β-d-glucopyranoside 1 under the agency of NIS/TfOH proceeds with high yields and good degrees of 1,2-cis stereoselectivity.