A solution of 0.38 g (2.4 mmol) of 2-chloro-4-fluorobenzaldehyde in 10 ml of isopropanol is heated together with 0.46 g (2.4 mmol) of the compound from Example VI, 0.48 g (2.4 mmol) of the compound from Example VIII and 0.24 g (2.88 mmol) of sodium acetate under reflux for 2 hours. The reaction mixture is concentrated, and the residue is taken up in dichloromethane and extracted with 2N hydrochloric acid. The aqueous phase is made alkaline with dilute ammonia solution and extracted with dichloromethane. The organic phase is washed with aqueous sodium chloride solution, dried over sodium sulfate and concentrated. The residue is chromatographed on silica gel with cyclohexane/ethyl acetate (20:1→10:1) as mobile phase, and the product is crystallized from diethyl ether.
