Abstract
Diverse electrophilic, nucleophilic and radical C-H trifluoromethylations of 1,3-dimethyluracil were systematically studied in order to prepare either 5- or 6-(trifluoromethyl)uracil derivatives. Electrophilic reagents led only to dimeric bis-uracil products, whereas the radical trifluoromethylation by CF3SO2Na in presence of t-BuOOH gave 1,3-dimethyl-5-(trifluoromethyl)uracil (2) in good yield.
The 6-(trifluoromethyl)uracil derivative 3 was only prepared in low yield and in a mixture with 2 by Ir-catalyzed borylation followed by treatment with the Togni's reagent. Attempted Pd-catalyzed C-H arylations of 2 in the presence of Cs2CO3 gave mixtures of de-trifluoromethylated products, whereas the reaction with 4-iodotoluene in the presence of CsF gave the desired 6-aryl-5-trifluoromethyluracil derivative 8 in moderate yield and the reaction was not general for other aryl halides.