Synthesis of sorbistin analogues

D-Galactose was converted into the glycosylating agents 4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alpha-D-glucopyranosyl chloride (11) and the methyl beta-D-thiopyranoside 19. Condensation of 11 with 2,5-diazido-1,6-di-O-benzoyl-2,5-di-deoxy-L-iditol in the presence of mercury salts gave 24% of 2,5-diazido-3-O-(4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alp ha-D- glucopyranosyl)-1,6-di-O-benzoyl-2,5-dideoxy-L-iditol. Methyl trifluoromethanesulfonate-promoted glycosylation of 1,3-diazido-2-O-benzyl-1,3-dideoxy-5,6-O-isopropylidene-D-gulit ol with 19 in the presence of 2,6-di-tert-butyl-4-methylpyridine gave 1,3-diazido-4-O-(4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alp ha-D- glucopyranosyl)-2-O-benzyl-1,3-dideoxy-5,6-O-isopropylidene-D-gulitol (42), whereas, in the absence of base, migration of the O-isopropylidene group occurred, affording 1,3-diazido-6-O-(4-azido-2,3-di-O-benzyl-4-deoxy-6-O-propionyl-alp ha-D- glucopyranosyl)-2-O-benzyl-1,3-dideoxy-4,5-O-isopropylidene-D-gulitol in addition to 42.