Substitution of a p-toluenesulfonyloxy group in the sugar portion of uracilnucleosides by an alkyl group was investigated by using Gilman reagents (R2CuLi). In the cases of 5'-O-tosyl derivatives of 2', 3'-O-isopropylideneuridine, moderate vields of 5'-alkylated products were obtained. In contrast to this, the reactions of the corresponding 2'-deoxyuridine derivatives gave higher yields of products. A similar substitution reaction at the 3'-position of 2'-deoxyuridine derivatives was also examined.