title: Acyloxy neighboring-group participation in the acid-catalyzed cleavage of methyl 2,3-anhydro-beta-D-ribofuranoside.
abstract: The reaction of methyl 2,3-anhydro-beta-D-ribofuranoside with hydrogen bromide in an acetic acid-acetic anhydride solution leads to the formation of methyl 2,3-di-O-acetyl-5-bromo-5-deoxy-alpha,beta-D-xylofuranoside. Similar treatment of methyl 2,3-anhydro-5-O-benzoyl-beta-D-robofuranoside provided methyl 2-O-acetyl-3-O-benzoyl-5-bromo-5-deoxy-alpha,beta-D-xylofuranosides. The position of halogen substitution was ascertained by hydrogenolysis to the resultant 5-deoxy sugars, which were characterized by their n.m.r. spectra. Confirmation of the structural assignment for methyl 2-O-acetyl-3-O-benzoyl-5-deoxy-alpha,beta-D-xylofuranoside was obtained by synthesis from 1,2-O-isopropylidene-alpha-D-xylofuranose. The formation of the 5-bromo derivatives under the reported conditions probably occurred through the intermediacy of the 3,5-acyloxonium ions. Similar conversions were observed when the starting compound was treated with hydrogen chloride, acetyl bromide, or acetyl chloride in acetic acid-acetic anhydride solutions.
mesh_terms: D001966:Bromine; D002845:Chromatography; D002855:Chromatography, Thin Layer; D003837:Deoxy Sugars / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D008722:Methods; D008759:Methylglycosides; D012266:Ribose / Q000031:analogs & derivatives*; D012822:Silicon Dioxide; D014994:Xylose / Q000031:analogs & derivatives*
chemical_list: D003837:Deoxy Sugars; D008759:Methylglycosides; D012266:Ribose; D012822:Silicon Dioxide; D014994:Xylose; D001966:Bromine