5‐Aroylamino‐3H‐1,3,4‐thiadiazole‐2‐thiones 2 have been synthesized by acylation of 5‐amino‐3H‐1,3,4‐thiadiazole‐2‐thione 1. 5‐Aroylamino‐3H‐1,3,4‐thiadiazole‐2‐thiones can exist in two tautomeric forms — a thiol form and a thione form. On the basis of the 13C nmr spectra and additional experimental information, it has been established that the thione form is the stable form in which these compounds exist.
5‐Aroylamino‐2‐methyl‐2H‐1,2,4‐thiadiazol‐3‐ones 3 have been synthesized by oxidative cyclization of 1‐aroyl‐5‐methyl‐2‐thiobiurets 2 with hydrogen peroxide in an alkaline solution. The needed 1‐aroyl‐5‐methyl‐2‐thiobiurets 2 have been obtained through the addition of methylurea to the corresponding aroyl isothiocyanates.
In the presence of ammonia, methyl N‐(bromoacetyl)anthranilate (4) is cyclized into 3H‐1,4‐benzodiaze‐pine‐2,5(1H,4H)‐dione (1). However, when 4 is replaced with methyl N‐(chloroacetyl)anthranilate (6), the only heterocyclic product formed in the reaction is 2‐(chloromethyl)quinazoline‐4(3H)‐one (7). Under analogous conditions, 3‐haloacetamidocrotonates (9, 10) do not yield any heterocyclic products and no 1,4‐diazepines can be obtained.
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