Cyclization of 2-amino-4-methyl-3-[2-aryl(hetaryl)-2-oxoethyl]-thiazolium bromides in aqueous medium. A simple synthesis of substituted imidazo[2,1-b]thiazoles

Abstract

Relatively large number of natural and biologically active compounds contain an imidazo[2,1-b]thiazole fragment [1–3]. Among a broad spectrum of biological activity intrinsic to imidazo[2,1-b]thiazole derivatives, immunosuppressive [4], inotropic [5, 6], and antiallergic activity [7] should be noted. However, no general methods for the synthesis of this heterocyclic system have been reported. The most widely used procedure is based on the reaction of α-halo ketones with substituted 2-aminothiazoles. There are some versions of this procedure, e.g., preliminary heating of a mixture of reactants to obtain N-alkylthiazole and its subsequent cyclization in an organic solvent (ethanol, butan-1-ol, toluene) or in the presence of aqueous HCl [8, 9] or one-pot synthesis in an appropriate organic solvent [8, 10–13]. As a rule, these procedures are not free from some disadvantages, the main of which are low yield (20–60%) and difficult isolation of the target product (chromatographic separation is often required).