5-Trifluoromethyluracil, an important intermediate for the preparation of the antiviral trifluridine, is obtained by chlorinating thymine to give the new 2, 4-dichloro-5- trichloromethylpyrimidine. Reacting the latter with hydrogen fluoride yields the new 2, 4- difluoro-5-trifluoromethylpyrimidine, and hydrolysis with water gives 5-trifluoromethyluracil in high purity and good yield.
