N-[3-(4-bromo-1H-pyrazol-3-yl)-2,4-difluoro-phenyl]-2,5-difluoro-N-(2-methoxy-ethoxymethyl)-benzenesulfonamide (584 mg, 1.085 mmol) was dissolved in DCM (5 mL). 32% sodium hydroxide was added (5 mL) followed by ethyl iodide (0.13 mL, 1.628 mmol, 1.5 eq) and TBAB (58 mg, 0.18 mmol, 0.17 eq) and the biphasic mixture was vigorously stirred at room temperature for 3 hours. The reaction mixture was then diluted with DCM, washed with water and brine, dried over Na2SO4 and evaporated to dryness. The two ethyl pyrazole regioisomers have been separated by chromatography on silica gel (n-hexane/ethyl acetate 7:3): 308 mg (50% yield) of the desired regioisomer N-[3-(4-bromo-1-ethyl-1H-pyrazol-3-yl)-2,4-difluoro-phenyl]-2,5-difluoro-N-(2-methoxy-ethoxymethyl)-benzenesulfonamide were obtained along with 160 mg (26% yield) of the minor regioisomer N-[3-(4-bromo-2-ethyl-2H-pyrazol-3-yl)-2,4-difluoro-phenyl]-2,5-difluoro-N-(2-methoxy-ethoxymethyl)-benzenesulfonamide.
