A solution of 6H-dibenzo[c,e]-1,2-thiazine 5,5-dioxide (1.7 g) in dry N,N-dimethylformamide (15 cc) is added dropwise to a suspension of sodium hydride (0.25 g, 80% suspension in oil) in N,N-dimethylformamide (5 cc). After 30 minutes' stirring, a solution of 1-(3-chloropropyl)-4-(4-fluorobenzoyl)piperidine (2.1 g) in N,N-dimethylformamide (15 cc) is added. The reaction mixture is heated to 100° C. for 40 minutes and is then cooled and poured into a mixture of water (150 cc) and ethyl acetate (150 cc). The organic phase is washed with water (3×50 cc), is dried over magnesium sulphate and is concentrated to dryness under reduced pressure (2.7 kPa). The residue is chromatographed on a column of silica gel (0.06-0.2-mm particle size, 2-cm diameter, 25-cm height) and eluted with a mixture of cyclohexane and ethyl acetate (50--50 by volume), 30-cc fractions being collected; fractions 7 to 16 are combined and concentrated to dryness under reduced pressure (2.7 kPa). The residue is recrystallized from ethanol (40 cc); the crystals obtained are filtered off, washed with ethanol (5 cc) and dried. 6-[3-(4-(4-fluorobenzoyl)-1-piperidyl)propyl]-6H-dibenzo[c,e]-1,2-thiazine 5,5-dioxide (1.8 g) is obtained, melting at 114° C.
