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.