Reaction kinetics and mechanism of acid-catalyzed anomerization of 1-O-acetyl-2,3,5-tri-O-benzoyl-l-ribofuranose

The mechanism of the acid-catalyzed anomerization of 1-O-acetyl-2,3,5-O-benzoyl-α- and -β-l-ribofuranoses in different acetic acid–acetic anhydride mixtures was investigated. The progress of the reactions was followed by NMR spectroscopy and the rate constants for the reactions were determined by the use of a kinetic model. The site of anomeric activation was clarified by the use of 13C-labeled acetic acid and acetic anhydride, respectively, proving that the anomerization takes place by exocyclic C–O cleavage, thus ruling out anomerization via acyclic intermediates. The role of the acetyl cation as the catalytically active species was further verified.

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