Perfluoroalkyllithiums generated in situ from perfluoroalkyl iodides and methyllithium add to 2,4-dichloropyrimidines in the presence of boron trifluoride etherate to give 4-perfluoroalkyl-3,4-dihydropyrimidines, which are converted to 6-perfluoroalkyl-5,6-dihydrouracils on hydrolysis, and to 6-perfluoroalkyluracils by oxidation with dichlorodicyano-1,4-benzoquinone (DDQ) followed by hydrolysis.