Heterocyclic systems containing bridgehead nitrogen atom: Part LXVI. Studies of orientation of cyclization in the synthesis of 8-fluorothiazolo[3,2-]benzimidazol-3(2)-one

Abstract 2-Fluoro-6-nitroaniline, obtained by nitration of 2-fluoroacetanilide, on reduction with Raney nickel and hydrazine hydrate followed by treatment of the resulting diamine with carbon disulphide in situ gives 4-fluorobenzimidazolyl-2-thione. This thione on condensation with chloroacetic acid gives 4-fluorobenzimidazol-2-thiolacetic acid which on cyclization with a mixture of acetic anhydrite and pyridine furnishes 8-fluorothiazolo[3,2- a ]benzimidazol-3(2 H )-one and not the alternate possible isomer, 5-fluorothiazolo[3,2- a ]benzimidazol-3(2 H )-one as revealed by 1 H-NMR spectroscopy. The condensation of 4-fluorobenzimidazolyl-2-thione with 1,2-dibromoethane yields 2,3-dihydro-8-fluorothiazolo[3,2- a ]benzimidazole and sym -bis-(4-fluorobenzimidazol-2-ylmercapto)ethane.