At 0° C., 0.500 g (4.46 mmol) of potassium tert-butoxide is added to 1.08 g (2.97 mmol) of the compound from Example 3A in 21 ml of DMF, and the mixture is stirred at room temperature for 30 min. 0.571 g (3.27 mmol) of 2-chloro-1-fluoro-4-nitrobenzene is added, and the mixture is stirred at RT. After 4.5 h, 200 ml of water are added, and the mixture is then extracted three times with ethyl acetate. The combined organic phases are washed with water and then dried over sodium sulphate. After filtration, the solvents are removed under reduced pressure. The residue is purified by chromatography on silica gel (cyclohexane/ethyl acetate 9:1). This gives 872 mg (56% of theory) of the desired compound.
