Oxidative halogenation of 6-methyluracil

摘要

An efficient method has been developed for the preparation of halo derivatives of 6-methyluracil by employing oxidative halogenation. Elemental halogens and potassium halides were used as the halogenating agents, while NaNO_3 and H_2O_2 were used as the oxidizing agents. Iodination of 6-methyl-uracil leads to 5-iodo-6-methyluracil as the single reaction product, while bromination or chlorination lead to 5-halo-6-methyluracil, 5,5-dihalo-6-hydroxy-6-methyl-5,6-dihydrouracil, or their mixture depending on the acidity of the medium and the ratio of the substrate and reagents. Bromination of 5-chloro-6-methyluracil leads to 5-bromo-5-chloro-6-hydroxy-6-methyl-5,6-dihydrouracil, while chlorination of 6-methyl-, 5-bromo-6-methyl-, and 5-chloro-6-methyluracils using gaseous chlorine yields 5,5-dichloro-6-hydroxy-6-methyl-5,6-dihydrouracil.