A mixture of 5.0 g of 11-(4-chlorobutyrylamino)-6,11-dihydrodibenzo[b,e]thiepin, 5.5 g of 1-(4-fluorophenyl)piperazine, 5.0 g of sodium iodide and 50 ml of dimethylformamide is stirred at 100° C. for 1.5 hours. After the reaction mixture is cooled to room temperature, 100 ml of 10% aqueous potassium carbonate solution is added and the solution is extracted with three 300-ml portions of chloroform. The combined extracts are washed successively with water and saturated aqueous sodium chloride solution, and dried over magnesium sulfate, and the chloroform is distilled off. The residue is chromatographed on silica gel with chloroform-methanol (100:3) to give 5.0 g of the title compound. m.p. 194°-194.5° C. (recrystallized from chloroform-n-hexane);
