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0 °C

To a solution of methyl 3-amino-4-fluorobenzoate (25 g, 149 mmol) in DCM (150 mL) were added pyridine (35.3 g, 446 mmol) and a catalytic amount of DMAP (1.8 g, 14.9 mmol). The mixture was cooled to 0° C. 2,5-Difluorobenzene-1-sulfonyl chloride (34.7 g, 212 mmol) in DCM (20 mL) was added dropwise to the mixture. The reaction was stirred at rt overnight. Then the reaction was washed with water (300 mL), and extracted with DCM (2×400 mL). The organic layer was washed with brine, dried over anhydrous NaSO4, filtrated and concentrated under reduced pressure to give the crude product, which was washed with petroleum ether to afford the title compound of Step A (48.2 g, 94.5% yield). 1H NMR (400 MHz, CDCl3) δ ppm 8.12-8.18 (m, 1H), 7.73-7.80 (m, 1H), 7.47-7.53 (m, 1H), 7.10-7.25 (m, 1H), 7.00-7.07 (m, 1H), 3.86 (s, 3H).

1. washThen the reaction was washed with water (300 mL)
2. extractionextracted with DCM (2×400 mL)
3. washThe organic layer was washed with brine
4. dry with materialdried over anhydrous NaSO4
5. filtrationfiltrated
6. concentrationconcentrated under reduced pressure
7. customto give the crude product, which
8. washwas washed with petroleum ether