An Unexpected Isomerization of N‐Aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines to 2‐(Benzothiazol‐2‐yl)‐2‐nitroethene‐l, l‐diamines

The syntheses of several N‐aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines 12 from 3, 3‐diamino‐2‐nitro‐thioacrylamides 11 are reported (Scheme 3). In polar solvents, a spontaneous isomerization of some of the prepared isothiazol‐5(2H)‐imines 12 yielded benzothiazoles 13 (Scheme 4). In the case of 2‐alkyl‐substituted derivatives of type 12, the isomerization occurred only at higher temperatures. Electronic influences of different substituents on the rate of the isomerization were studied, and a polar reaction mechanism is proposed in Scheme 6. The structures of 12e and 13e were established by X‐ray crystallography. Conformational analyses of 3‐(methylamino)‐2‐nitro‐N‐phenyl‐3‐(pyrrolidin‐1‐yl)thioacrylamide (111) by NMR and X‐ray methods were performed with the aim of explaining the distinct behavior of this amide towards Br2 or diethyl azodicarboxylate.