Reaction of 2-Mercapto-4-chloro-6-bromobenzimidazole with Chloroacetic acid, α-Halogenoketones and Alkyl Bromides

Department of Chemistry, Kurukshetra University, Kurukshetra-132 119

The syntheses of 6-bromo-8-chlorothiazolo[3,2-a]benzimidazol-3(2H)-one (4), 3- aryl-6-bromo-8-chlorothiazolo[3,2-a]benzimidazoles (6), 2,3-dihydro-6-bromo-8-chloro­thiazolo[3,2-a]benzimidazole (7) and 4H-2,3-dihydro-7-bromo-9-chloro[1,3]thiazino­ [3,2-a]benzimidazole (8) have been achieved starting from 2-mercapto-4-chloro-6-bromo­benzimidazole (2). Compound 2, obtained by the reaction of 4-bromo-6-chloro-1,2- diaminobenzene (1) with carbon disulphide, on condensation with chioroacetic acid gives the acid 3, which on cyclisation with acetic anhydride furnishes 4, and not the other isomer 9 as revealed by pmr spectral data. Condensation of 2 with \(\alpha\)-halo­genoketones followed by PPA cyclisation of the intermediate ketone (5) yields 6. Similarly, the reaction of 2 with 1,2-dibromoethane and 1,3-dibromopropane gives 2,3-dihydro-6-bromo-8-chlorothiazoloI3,2-albenzimidazole (7) and 4H-2,3-dihydro-7- bromo-9-chloro[1,3]thiazino [3,2-a] benzimidazole (8), respectively