Whereas BAIB-TEMPO oxidation of 2’,3’-O-TBDMS-N4-acetylcytidine results in the expected 5'-carboxylic acid nucleoside, its 2',3'-O-isopropylidene analogue reacts in a radically different way. We have demonstrated here that hypervalent iodine(III) in water triggers an unprecedented oxidative cyclization leading to a mixture of C5-substituted O6,5'-cyclo-5,6-dihydro-uridines. This mixture of cyclouridines can be opened under basic conditions and, after deprotection, yields 5-hydroxyuridine, an important post-transcriptional modification of uridine at the wobble position (U34) of bacterial tRNA. NMR experimental values and calculations were performed to provide further insight on the specific reactivity of 2',3'-O-isopropylidene N4-acetylcytidine.