Synthesis and properties of 5‐aroylamino‐2 H ‐1,2,4‐thiadiazol‐3‐ones

5 ‐Aroylamino‐2 H ‐1,2,4‐thiadiazol‐3‐ones 3 were obtained from the corresponding 1‐aroyl‐2‐thiobiurets 2 by oxidative cyclization with bromine. 5 ‐Aroylamino‐2 H ‐1,2,4‐thiadiazol‐3‐ones 3 can exist in two tautomeric forms a lactam form and a lactim form. On the basis of the 13 C nmr spectra and additional experimental information, it has been established that the stable form, in which these compounds exist, is the lactam form.