On the reaction of isothiosemicarbazides with heterocumulenes. Part I

Isothiosemicarbazides 2 react with acyl isothiocyanates under addition‐cyclization to yield 1,3,4‐thiadiazoline‐2‐imines 3 as well as the isomeric 2‐amino‐substituted 1,3,4‐thiadiazolium‐5‐acylaminides 3′ . In a similar manner the 2‐hydrazino‐substituted 1,3‐thiazoline 4 adds ethoxycarbonyl isothiocyanate to give the thiosemicarbazide 5 , which undergoes a rearrangement to the 1,3,4‐thiadiazoline‐2‐imine 5′. The [2+2] cycloreversion of 3d involving ethoxycarbonyl iso(thio)cyanate and the thermal induced Dimroth rearrangement of 3′f and h are also discussed.