Smiles rearrangement—XV: The S→N type rearrangement in uracil derivatives

The reaction of 1,3-dimethyl-6-(2-acetamidophenylthio)uracil 6 with caustic alkali followed by methylation gave 1,3-dimethyl-6-(2-methylthioanilino)uracil 7 accompanied with 1,3-dimethyl-5-acetyl-6-(2-methythioanilino)uracil 8. Pyrimido[1,5]benzothiazepine 10 was obtained in high yield by the Smiles rearrangement of 6, trapping of the resulting thiolate ion with formalin and subsequent acid-catalysed cyclization. Treatment of 1,3-dimethyl-6-(2-aminophenylthio)uracil 5 with hot acetic acid gave 1,3-bis[(2-benzothiazolyl)acetyl]-1,3-dimethylurea 12. Upon heating 5 or N-acetyl derivative 6 in dimethylsulfoxide, 5-thiaisoalloxazine 3 was obtained in moderate yield. Mechanisms of the observed reactions were discussed.