Syntheses of various 5‐(bromoaryl)‐substituted uracils

The Suzuki Pd(0)‐catalyzed coupling between arylboronic acids and aryl bromides or iodides in weakly alkaline medium, previously further developed by us, has been used for regioselective preparation of 5‐(2′‐bromo‐5′‐furyl)‐, 5‐(2′‐bromo‐4′‐furyl)‐, 5‐(2′‐bromo‐5′‐thienyl)‐, 5‐(2′‐bromo‐4′‐thienyl)‐, 5‐(4′‐bromo‐2′‐thiazolyl)‐, 5‐(3′‐bromophenyl)‐, 5‐(6′‐bromo‐2′‐pyridyl)‐ and 5‐(4′‐bromo‐2′‐pyrimidyl)‐substituted 2,4‐di‐t‐butoxypyrimidines. In the coupling between 2,4‐di‐t‐butoxy‐5‐pyrimidineboronic acid and the nine different aryl dibromides that were tried as coupling partners, only the 2,4‐ and 2,5‐dibromothiazoles did not give satisfactory yields, 15% and 0%, respectively. The other seven aryl dibromides gave the desired 5‐(bromoaryl)‐2,4‐di‐t‐butoxypyrimidines in 58‐89% yield. Attempts to synthesise 2,4‐di‐t‐butoxy‐5‐(2′‐bromo‐4′‐thienyl)pyrimidine from 2‐bromo‐4‐iodothiophene failed. Dealkylation of the 5‐(bromoaryl)‐2,4‐di‐t‐butoxypyrimidines in 2.5 M hydrochloric acid gave the corresponding 5‐(bromoaryl)uracils in almost quantitative yields.