Synthesis of various substituted fluoreno[1,2-d]imidazol-10-ones (5a-5g) has been accomplished by the cyclization of diazotized 1-substituted 4-benzoyl-5-aminobenzimidazoles (4a-4g). Compounds 4a-4g were prepared by reductive ring opening of 3H-imidazo[4',5':3,4]benzo[c]isoxazoles (3a-3g) with zinc dust in EtOH/NaOH solution.