Studies on the 6-homologation of β-D-idopyranosides.

β-D-Idopyranosides are interesting sugars because of their unusual conformational flexibility in the pyranosyl ring, and also their β-1,2-cis-anomeric configuration. Here we report our studies of the regioselective opening of 4,6-O-benzylidene-protected β-D-idopyranosides under reducing conditions, and the subsequent 6-homologation via Swern oxidation and Wittig olefination to afford a 6,7-dideoxy-β-D-ido-hept-6-enopyranoside. This olefination product was found to adopt predominantly C conformation in solution by NMR experiments, which places the vinyl group at a more sterically hindered axial position and creates difficulty in subsequent hydroborations.