To a solution of 4-(2-fluoro-4-nitrophenoxy)pyridin-2-ylamine (300 mg, 1.2 mmol) and triethylamine (0.335 ml, 2.4 mmol) in tetrahydrofuran (30 ml) was added phenyl chloroformate (0.226 ml, 1.8 mmol) dropwise while stirring in an ice bath, followed by stirring for 1 hr. The reaction mixture was concentrated under a reduced pressure to give a residue, to which was then added N,N-dimethylformamide (6.0 ml) and 1-methylpiperazine (537 μl, 4.84 mmol), followed by stirring at room temperature for 3 hrs. To the reaction mixture was added ethyl acetate (150 ml), washed with a saturated aqueous solution of sodium hydrogencarbonate, and dried over anhydrous sodium sulfate. The solvent was evaporated to give a residue, which was then purified by silica gel column chromatography (Fuji Silysia NH, eluent; hexane:ethyl acetate=1:2, then ethyl acetate) to provide the titled compound (450 mg, 75.3%) as a pale yellow oil.
