Palladium-catalysed carbomethoxyvinylation and thienylation of 5-iodo(bromo)-2,4-dimethoxypyrimidine in water

(E)-5-(2-Carbomethoxyvinyl)-2,4-dimethoxypyrimidine (2) was prepared in high yield (90%) at room temperature from 5-iodo-2,4-dimethoxypyrimidine (la) via the heterogenous Heck-reaction with methyl acrylate in aqueous solution containing n-Bu4NHSO4 and potassium carbonate. Under the same conditions, using thiophene and heating the mixture under reflux, 5-(2-thienyl)-2,4-dimethoxypyrimidine (3) was obtained in 50% yield starting from la, or in 37% yield starting from 5-bromo-2,4-dimethoxypyrimidine (Ib). Surprisingly, the use of la and thiophene at 150 degrees C in a pressure reactor (50 psi) resulted in a 23% yield of 6-(2-thienyl)-2,4-dimethoxypyrimidine (4) only. (C) 1997 Elsevier Science Ltd.