Research on heterocyclic compounds. XXI. Synthesis of imidazo[2,1‐b]benzothiazole and imidazo[2,1‐b]thiazole derivatives

The reaction of some 2‐aminobenzothiazoles and 2‐aminothiazoles with ethyl 3‐bromo‐4‐oxopentanoate was investigated with the aim to obtain the corresponding imidazo[2,1‐ b ]benzothiazole and imidazo[2,1‐ b ]‐thiazole derivatives, respectively. In some cases, two unexpected side products were obtained together with the required compound and their structures were elucidated: e.g. , 2‐aminobenzothiazole reacted with ethyl 3‐bromo‐4‐oxopentanoate to give ethyl 2‐methylimidazo[2,1‐ b ]benzothiazole‐3‐acetate together with ethyl imi‐dazo[2,1‐ b ]benzothiazole‐2‐propionate and ethyl 3‐(benzothiazol‐2‐yl)amino‐4‐oxopentanoate.