Chlorosulfonic acid → 5-Fluoro-2-oxo-2,3-dihydro-1,3-benzoxazole-6-sulfonyl chloride

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Reaction Steps

According to Scheme 11, a mixture of commercially-available 5-fluoro-1,3-benzoxazol-2(3H)-one (11-1, 1.02 g, 6.66 mmol) in DCM (66.6 ml) at RT was added chlorosulfonic acid (4.46 ml, 66.6 mmol). The suspension gradually became a solution and was stirred for 18 h at RT. Following this duration, LCMS showed complete consumption of starting material. The solution was cooled to 0° C. and carefully quenched with ice chips and then partitioned between water (100 mL) and EtOAc (100 mL). The layers were separated and the aqueous layer was back-extracted with 3×20 mL DCM and 2×20 mL EtOAc. The combined organic layers were washed with saturated aqueous NaHCO3 (30 mL), dried over sodium sulfate and filtered. Concentration in vacuo to yield 11-2 (5-Fluoro-2-oxo-2,3-dihydro-1,3-benzoxazole-6-sulfonyl chloride) as a tan solid, which was used without purification.

Provenance & Evidence