Abstract
4′‐Substituted 1‐arylcarbonyl‐5‐fluorouracil derivatives were synthesized from the reaction of the potassium salt of 5‐fluorouracil with one equivalent of aryl acid chloride in acetonitrile. 4′‐Substituted 3‐arylcar‐bonyl‐5‐fluorouracil derivatives were synthesized from the reaction of 5‐fluorouracil with 3 equivalents of the aryl acid chloride in pyridine and the subsequent hydrolysis of the 1,3‐diarylcarbonyl‐5‐fluorouracil derivatives in situ with a small amount of water. If a large amount of water were used in the second step, the 1,3‐diarylcarbonyl‐5‐fluorouracil precipitated before it hydrolyzed. The melting behaviors of both the 1‐arylcarbonyl‐5‐fluorouracil and 3‐arylcarbonyl‐5‐fluorouracil series suggested that thermal decomposition or rearrangement occurred on heating. The position of the C^6^‐H absorption in the ^1^H nmr spectra of 1‐arylcarbonyl‐5‐fluorouracils was 0.14 to 0.23 ppm farther downfield than that of the corresponding 3‐arylcarbonyl‐5‐fluorouracils while that of the 1,3‐diarylcarbonyl‐5‐fluorouracils was even farther downfield. The Rf values of 1‐arylcarbonyl‐5‐fluorouracils were significantly greater (0.23 to 0.41) than those of the corresponding 3‐arylcarbonyl‐5‐fluorouracils, while that of 1,3‐diarylcarbonyl‐5‐fluorouracil was slightly greater than that of 1‐arylcarbonyl‐5‐fluorouracils.