Abstract The 5-aryl (or methyl)-3-phenylcarbamoyl-1, 3, 4-oxadiazol-2 (3H)-ones 2, in the presence of sodium hydride in anhydrous dimethylformamide, were transformed into 1- benzamido (or acetamido)-3, 5-diphenyl-1, 3, 5-triazine-2, 4, 6-trione derivatives 7 in poor yields. However, compounds 7 were obtained in better yields when the sodium salts of 5- aryl (or methyl)-1, 3, 4-oxadiazol-2 (3H)-ones 1 were treated with two equivalents of aryl ( ...