Synthesis of nojirimycin C-glycosides

Nojirimycin alpha-C-glycosides, which have 1-alpha-allyl-1-deoxy-N-benzyl-2,3,4,6-tetra-O-benzylnojirimycin (9) as a key intermediate for further derivatisation, have been synthesized from commercially available 2,3,4,6-tetra-O-benzyl-glucopyranose (3) through a highly stereoselective procedure which involves treatment of 3 with benzylamine, reaction of the obtained glucosylamine 4 with allylmagnesium bromide and cyclization of the elongated open-chain aminosugar 5 by Fmoc-protection, oxidation of the free hydroxy group, and intramolecular reductive-amination, affording 9 in 59% overall yield. The efficient manipulation of the allylic appendage of 9 has required N-debenzylation and Fmoc-protection of the ring-nitrogen.