Methylglyoxalyl chloride arylhydrazones (III) react with an ethanolic solution of thiourea to give 2‐amino‐4‐methyl‐5‐arylazothiazoles (XII) instead of the expected 2‐acetyl‐4‐aryl‐5‐imino‐Δ2‐1,3,4‐thiadiazolines (V) which were obtained from III and potassium thiocyanate. 3‐Thiocyanato‐2,4‐pentanedione (IV) coupled with diazotized anilines to give V. The postulated routes to formation of V and XII from III are given. Nitrosation of V gave the corresponding N‐nitroso derivatives (VI) which decomposed upon refluxing in dry xylene to give 2,4‐disubstituted‐Δ2‐1,3,4‐thiadiazolin‐5‐ones (VII). Boiling of either V or VI with hydrochloric acid gave the hydrochloride salt (VIII). The thiadiazolines V gave the respective N‐acyl derivatives (IX) and (X) with acetic anhydride and benzoyl chloride in pyridine.
The azo coupling of dimethylphenacylsulfonium bromides (I) with N-nitrosoacetanilides in nonaqueous solvents, and with diazotized aniline in aqueous media gave 2-bromophenylglyoxal 2-arylhydrazones (V) and the tetrazine (VI), respectively. V reacted with nucleophiles displacing the bromide. Treatment of V with bases gave VI via benzoylphenylnitrilimine (X). 1,3-Dipolar cycloadditions of X onto ethyl acrylate and acrylonitrile afforded the expected cycloadducts. The mechanisms of the reactions are outlined.
Aus dem Rhodanid (I) erhält man mit den Diazoniumsalzen (II) die Thiadiazole (III), die auch aus den Chlorc‐hydrazonen (IV) mit Kaliumrhodanid erhalten werden.
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