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.

A synthesis of quinazolines, perimidines and dibenzo [d,f][1,3]diazepines is described. The method involves rearrangements following cyclisation of 2-anilino-2-methoxy-3-oxo-N-phenylbutanethioamides with aromatic 1,3and 1,4-diamines.