Upon oxidation followed by treatment with hydroxylamine, the 3',5'-diblocked uridine 1 gave the expected oxime 2 together with the N⁶,2'.cyclonucleoside 3 formed by nucleophilic attack of hydroxylamine at both C-6 and C-2' positions. Reduction of 2 took place predominantly from the α face and the major o-arabino compound obtained gave the cyclonucleoside 7via Michael type addition. The structures of the novel cyclonucleosides, particularly their configuration at C-6 were established by X-ray diffraction.