Synthesis of endocyclic enol methyl ethers of 3-acylthiotetronic acids and their reactions with amines

Acylation of (3H,5H)-tetrahydrothiophene-2,4-dione (thiotetronic acid) with acetyl, propionyl, and valeryl chlorides followed by O-C isomerization in the presence of 4-dimethylaminopyridine or acetone cyanohydrin gave rise to 3-acetyl, 3-propanoyl, and 3-pentanoyl derivatives of thiotetronic acid. The reaction of 3-acylthiotetronic acids with diazomethane afforded enol methyl ethers at the endocyclic keto groups. The subsequent reaction of these enol ethers with allylamine, benzylamine, and p-anisidine occurs along the mechanism of vinylog substitution providing the corresponding endocyclic enamino derivatives.