Selective cyclization of S-substituted imidazolethione: synthesis of polysubstituted imidazothiazoles

Abstract

2-Mercapto-5(4)-methylimidazole-4(5)-carboxanilide (2), was prepared directly by the reaction of α-aminoacetoacetanilide (1) with ammonium thiocyanate in acetic acid containing a catalytic amount of hydrochloric acid. Alkylation of 2 with alkyl halides or proper α-haloketones led to the formation of the corresponding 2-substituted alkylthio derivatives (3a–e). Cyclization of 3c–e by boiling with acetic anhydride in pyridine or by heating with polyphosphoric acid, led to the formation of 2-(un)substituted-3-substituted-6-methylimidazo[2,1-b]thiazole-5-carboxanilides (4a–c). These synthesized compounds were characterized by EL-MS, NMR spectroscopy and by chemical evidences (compounds were prepared by direct and step-wise methods).