1,3-Cyclohexanedione (I) was brominated in cold water, and the resulting 2-bromo-1,3-cyclohexanedione (II) was condensed with 2-aminopyridine (III) in boiling EtOH to afford the dihydropyridobenzimidazolone (IV). Further bromination in concentrated HBr at 70 C gave bromoketone (V), which was finally condensed with thiourea (VI) in EtOH to yield the target tetracyclic compound.