2-Amino-3-methoxycarbonylmethylthiazolium bromide (IV) reacted with ketenethioacetal derivatives (IIa-d) in the presence of sodium hydride or triethylamine to afford stable intermediate, 2-imino-2, 3-dihydrothiazole derivatives (Va-e). Va, b, d were treated with sodium methylate to give imidazo [2, 1-b] thiazole derivatives (IXa-c) by intramolecular nucleophilic substitution reactions.
