Abstract Derivatives of a novel tricyclic system having a 1, 5-benzothiazepine skeleton are described. A method for synthesis of the title compounds 5, consisted of an intramolecular cyclization of 1-(2-carboxymethylthiophenyl)-2 H-imidazol-2-ones 4 in PPA, is presented. Compounds 4 were prepared by a reaction of 1-(2-mercaptophenyl)-2 H-imidazol-2-ones 3 with chloroacetic acid. 2 H-Imidazolones 3 were obtained by a ring transformation of ...