Unexpected rearrangement products from animations of 5‐bromo‐2‐nitrothiazole

While reaction of 2‐bromo‐5‐nitrothiazole (2) with weakly basic secondary aliphatic amines gives the expected 2‐amino products from nucleophilic displacement of the bromine, reaction of the isomeric 5‐bromo‐2‐nitrothiazole (3) with such amines gives mixtures of the expected 5‐amino products together with 2‐aminated 5‐nitrothiazole rearrangement products. The identity of the latter were detemined by alternative synthesis, and by X‐ray crystallographic determination of a derivative. The mechanism proposed is a slow thermal isomerization of 5‐bromo‐2‐nitrothiazole (3) to the much more reactive 2‐bromo‐5‐nitro isomer 2 which competes, in the case of relatively weak amine nucleophiles, with the direct (but slow) nucleophilic displacement of the 5‐bromo group to form the normal displacement products.