investigates. A stable 2′-O-triflyl derivative, that of N-nitro-3′,5′-O-(tetraisopropyldisiloxane-1,3-diyl)uridine, has been isolated for the first time; by contrast to its congeners, it does not give cyclonicleoside-like intermediates. Nucleophilic attacks on this substrate lead to 2′ß-substituted nucleosides rather than the usual 2′α epimers. 3′-O-Triflyl N-nitro derivatives behave similarly. Several