Methanesulfonyl chloride → Ethyl 2-[(2-[(methylsulfonyl)oxy]-4-{[5-(methylsulfonyl)pyridin-2-yl]oxy}phenyl)hydrazono]propanoate

To a solution of ethyl 2-[(2-hydroxy-4-{[5-(methylsulfonyl)pyridin-2-yl]oxy}phenyl)-hydrazono]propanoate (37.7 g) in pyridine (450 mL) was added methanesulfonyl chloride (8.9 mL) at 0° C., and the mixture was stirred at room temperature for 1 h. Methanesulfonyl chloride (8.9 mL) was added to the mixture at 0° C. again, and the mixture was stirred at room temperature for 1 h. Furthermore, methanesulfonyl chloride (8.9 mL) was added to the mixture at 0° C., and the mixture was stirred at room temperature for 15 h. The mixture was concentrated under reduced pressure. Water was added to the residue and the mixture was extracted with ethyl acetate-tetrahydrofuran. The organic layer was washed successively with 1M hydrochloric acid, water, saturated aqueous sodium hydrogen carbonate solution and saturated brine, dried over magnesium sulfate, filtered and concentrated. The residual solid was washed with diethyl ether to give the title compound (37.05 g, 83%) as an off-white solid. MS 472 (MH+).