In the reactions of acetylthioacetanilides (1a–c) and diacetylthioacetanilides (3a–f) with phosgene 1,3‐thiazetidine‐2‐one (2a–c) and 1,3‐oxazine‐2‐one (5a–f) were obtained respectively. The structures of new compounds were elucidated by elemental analyses, i.r., 1H‐n.m.r., m.s., for 1d–f by 19F‐n.m.r. and for 2a and 5a by 13C‐n.m.r. spectral data.

An NMR study of the equilibrium between keto-enol tautomeric forms of N-aryl-diacetylthioacetamides enables us to estimate their population ratio in solvents of increasing polarity. An X-ray analysis confirmed the structure of the thermodynamically most stable tautomer. We presume that the course of heterocyclization processes with N-aryldiacetylthioacetamides is affected by the structure of the reacting tautomeric form. The treatment of N-aryldiacetylthioacetamides with oxalyl or bromoacetyl bromides leads to thiazolidine derivatives. The reactivity of the 5-methylene group in the obtained thiazolidin-4-one derivatives was investigated.

The title compounds (III) are stable in weak acidic medium and cleaved in alkaline or alcoholic solution.

No abstract

The acetanilides (Ia) and (IV), which both exist as tautomeric mixtures, react with phosgene (II) to give the title systems (III) and (V), respectively.