The reaction of 4-ethoxy-1-(3, 5-O-tetraisopropyldisiloxanyl-1, 3-diyl-β-D-erythro-pentofuran-2-ulosyl)-2(1H)-pyrimidinone (11) with various organometallic reagents yielded corresponding 2'-branched-chain sugar pyrimidine nucleosides. Only in the reactions with MeMgBr and EtMgBr was the more hindered β-attack observed to afford and 2'-alkyl ribofuranosides (13a, b). In the reaction of 11 with MeLi, Me₃, Al, or PhMgBr, 2'-methyl or phenyl arabinosides (12a, b, c)were obtained stereoselectively. Conversion of these pyrimidine nucleosides into cytosine derivatives is also described and their antileukemic and antiviral activities are discussed.