The catalytic trifluoromethylation Of Uracil using CF3I was investigated to find a new industrial process for the production of 5-trifluoromethyluracil. The catalytic system of FeSO4, H2O2 and H2SO4 in dimethylsulfoxide efficiently and selectively yielded 5-trifluoromethyluracil under mild conditions. FeSO4 exhibited the highest activity among the Fe(II) compounds tested. H2O2 was indispensable for the reaction and only Fe(II) Compounds yielded the desired product. This characteristic of the reaction suggests that it proceeds in a Fenton oxidation manner. The reaction was applicable to large-scale production: 50 kg of 5-trifluoromethyluracil in a 600 L reactor. By the use of this catalytic system, selective trifluoromethylation at the 5-position was also performed with various uracil derivatives including uridines. Interestingly, Cp2Fe was superior to FeSO4 for several substrates. (c) 2008 Elsevier B.V. All rights reserved.