An unusual course of thioglycoside activation with bromine: synthesis and crystal structure of 4-O-acetyl-2-bromo-2,3,6-trideoxy-3-C-methyl-3-trifluroacetamido-α-l-altropyranosyl bromide Original Research Article

Bromine activation of phenyl 4-O-acetyl-2,3,6-trideoxy-3-C-methyl-3-trifluoroacetamido-1-thio-α,β-l-ribo-hexopyranoside and attempted coupling with an acceptor in the presence of silver silicate gave an unusual bicyclic product, 2-trifluoromethyl-(4-O-acetyl-2-bromo-2,3,6-trideoxy-3-C-methyl-α-l-altrohexopyrano)-[3,2,1-d,e]-2-oxazine, instead of the expected disaccharide. Detailed investigation supported by X-ray crystallographic analysis showed that a trans dibromide is an intermediate in this reaction and that the dibromide is likely formed from a glycal that is generated by elimination during the coupling step.