1-(2-Oxocyclobutyl-4-benzoyloxymethyl)-2,4(1H,3H)-pyrimidinedione and 1-(2-oxocyclobutyl-4-benzoyloxymethyl)-5-methyl-2,4(1H,3H)-pyrimidinedione can be prepared by reaction of uracil and thymine, respectively, with 3-benzoyloxymethyl-2-bromocyclobutanone. The N-alkylation gave both cis and trans isomers with the trans isomer predominating for uracil whereas the trans isomer was the only product which could be isolated for thymine. Both series were subjected to borohydride reduction followed by transesterification with methoxide giving the corresponding uracil and thymine nucleoside analogues. The uracil derivative 1-(2-oxocyclobutyl-4-benzoyloxymethyl)-2,4(1H,3H)-pyrimidinedione was irradiated in aqueous acetonitrile to generate isonucleoside analogues.