To a solution of 260 mg of the mixture of methyl 6-iodo-5-oxo-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-1-carboxylate and its 4-iodo form prepared in Example 6-c in 10 ml carbon tetrachloride were added 130 mg of N-bromosuccinimide and 5 mg of azobisisobutyronitrile, followed by heating under reflux for 2 hours. The reaction mixture was cooled to room temperature and filtered. The filtrate was washed with diethyl ether, and the solvent was removed. To the residue was added 10 ml of dimethylformamide, and further added 0.15 ml of 1,8-diazabicyclo[5.4.0]undecene at room temperature, followed by stirring at room temperature for 10 minutes. Water was added to the reaction mixture, and the mixture was extracted with ethyl acetate. The organic layer was washed with water, dried over anhydrous magnesium sulfate, and the solvent was evaporated. The residue was purified and separated by silica gel column chromatography (ethyl acetate:hexane=1:4), to give 200 mg of a mixture of the title compound with its 4-iodo form as a colorless powder.
