Chlorosulfonic acid → ethyl 2-(3-(2-(chlorosulfonyl)benzyl)-5-fluoro-2-methyl-1H-indol-1-yl)acetate

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Reaction Steps

Sodium 2-((1-(2-ethoxy-2-oxoethyl)-5-fluoro-2-methyl-1H-indol-3-yl)methyl)benzenesulfonate (2.30 g, 5.38 mmol) was added portionwise to chlorosulfonic acid (10 ml) at room temperature (20° C.) over 20 min. The resulting mixture was stirred at room temperature for 2 hours, then poured onto ice/water (300 mL). The solution was next extracted with CH2Cl2, and the separated organics washed with water, dried over anhydrous magnesium sulfate, filtered and evaporated in vacuo to afford ethyl 2-(3-(2-(chlorosulfonyl)benzyl)-5-fluoro-2-methyl-1H-indol-1-yl)acetate (2.03 g, 4.79 mmol, 89%), which was used in the next step without further purification.

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