Bromohydroxylation of glycals - An investigation into the reaction of some 4-N-acylated derivatives of methyl 5-acetamido-7,8,9-tri-O-acetyl-2,6-anhydro-3,4,5-trideoxy-D-glycero-D-galacto-non-2-enonate and its 4-epimer

Bromohydroxylation of some 4-N-acylated derivatives of the glycals of N-acetylneuraminic acid, methyl 5-acetamido-7,8,9-tri-O-acetyl-2,6-anhydro3,4,5-trideoxy-D-glycero-D-galacto-non-2-enonate (4) and methyl 5-acetamido-7,8,9-tri-O-acetyl-2,6-anhydro-3,4,5-trideoxy-D-glycero-D-talo-non-2- enonate (the 4-epimer of 4), with N-bromosuccinimide (NBS) and water in the presence of a co-solvent has provided a range of new glycosyl donors. The stereoselectivity of the halohydroxylation reaction was found to be governed by solvent composition, reaction temperature and the stereo electronic nature of the substituent at C-4.