To secondary amine 30 (150 mg, 0.35 mmol, 1 eq.) in dry DCM (15 mL) at 0° C. was added Et3N (3 mL) followed by dropwise addition of a DCM solution of 4-fluorobenzenesulfonyl chloride (90 mg, 0.42 mmol, 1.2 eq). After stirring at 0° C. for 20 min, the mixture was stirred at room temperature for 2 h. The reaction was extracted between DCM and water and the organic layer was washed with 1N HCl, saturated NaHCO3 solution, and brine, dried (Na2SO4), and concentrated in vacuo to give 150 mg (72%) of t-butyl 2-((4-fluoro-3-(methylsulfonyl)phenyl)-4-((4-fluoro-N-methylphenylsulfonamido)methyl)phenoxy)acetate (31) as oil which was used in the next step without further purification.
