The ribo- and arabinofuranosyl nucleosides of antitumor active 2- and 4-pyridones 1a and 2a were prepared by direct condensation of the silylated bases with either 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose (4a) or 2,3,5-tri-O-benzyl-1-p-nitrobenzoyl-D-arabinofuranose (7) in the presence of