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( E )-5-(2-Carbomethoxyvinyl)-2,4-dimethoxypyrimidine ( 2 ) was prepared in high yield (90%) at room temperature from 5-iodo-2,4-dimethoxypyrimidine ( 1a ) via the heterogenous Heck-reaction with methyl acrylate in aqueous solution containing n-Bu 4 NHSO 4 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 1a , or in 37% yield starting from 5-bromo-2,4-dimethoxypyrimidine ( 1b ). Surprisingly, the use of 1a and thiophene at 150° C in a pressure reactor (50 psi) resulted in a 23% yield of 6-(2-thienyl)-2,4-dimethoxypyrimidine ( 4 ) only. |
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