The reaction of isothiocyanates with 2‐cyanoethanoic acid hydrazide. A novel synthesis of 1,3,4‐thiadiazoles

Benzoyl and ethoxycarbonyl isothiocyanates reacted with 2‐cyanoethanoic acid hydrazide 2 to afford 1‐cyanoacetyl‐4‐substituted thiosemicarbazide ( 5a,b ). Compound 5a afforded the pyrazolo[1,5‐ a ]‐ s ‐triazine derivative 6 on treatment with 5% potassium hydroxide, and cyclised to 2‐benzoylamino‐5‐cyanomethyl‐1,3,4‐thiadiazole ( 8 ) when boiled under reflux in glacial acetic acid. Compound 8 condensed with aromatic aldehydes to yield the corresponding arylidene derivatives 9a‐c . It undergoes coupling with aromatic diazonium salts to afford the hydrazones 11a‐c . Similarly, it coupled with diazotised aminopyrazole to afford the cyclic product 12 .