The Cyclopropyliminium Rearrangement of Cyclopropylthiazoles

2-Cyclopropylthiazole hydrobromides undergo iminocyclopropane-pyrroline rearrangement in a melt to give the corresponding fused heterocycles, viz. 6,7-dihydro-5H-pyrrolo[2,1-b]thiazol-4-ium bromides. 2-Alkyl- and 2-aryl-4-cyclopropylthiazoles transform into analogous fused heterocycles as hydroiodides and noticeably longer.