Stereoselective Access to Iminosugar C , C -Glycosides from 6-Azidoketopyranoses.

We report the synthesis of iminosugar C , C -glycosides starting from 6-azidoketopyranoses. Their Staudinger-azaWittig-mediated cyclization provided bicyclic N , O -acetals, which were stereoselectively opened with AllMgBr to afford β-hydroxyazepanes with a quaternary carbon α to the nitrogen. Their ring contraction via a β-aminoalcohol rearrangement produced the six-membered l-iminosugars with two functional handles at the pseudoanomeric position. Inversion of the free OH at the azepane level furnished the d-iminosugars.