Alkylation of 6-Polyfluoroalkyl-2-thiouracils with Haloalkanes

Abstract

The structure of 6-polyfluoroalkyl-2-thiouracils and reactivity of nucleophilic centers in their molecules were analyzed by quantum chemical calculations. According to the experimental data, methylation of 6-polyfluoroalkyl-2-thiouracils with methyl iodide initially gives 2-methylsulfanyl-substituted pyrimidin-4-one and then S,N3- and S,O-dimethyl derivatives. The optimal conditions for the selective formation of the S, N3- isomer were heating in tert-butyl alcohol in the presence of cesium carbonate as a base. Ethylation of 6-polyfluoroalkyl-2-thiouracils afforded approximately equal amounts of S,N3- and S,O-dimethyl derivatives. S,N3-Dimethyl-substituted pyrimidines in boiling ethanol in the presence of potassium carbonate were converted into uracil potassium salts as a result of nucleophilic substitution of the methylsulfanyl group by ethoxy and subsequent dealkylation of the latter.