Trifluoroacetic anhydride → Perfluorophenyl 1-bromo-3-chloroisoquinoline-6-sulfonate

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Reaction Steps

A round-bottom flask was charged with perfluorophenyl 3-chloroisoquinoline-6-sulfonate (1.21 g, 2.95 mmol) and DCM (11.81 ml) to give a clear solution. Urea compound with hydrogen peroxide (1:1) (0.556 g, 5.91 mmol) was added, resulting in a suspension. The flask was cooled in an ice-water bath for 10 min, then 2,2,2-trifluoroacetic anhydride (0.834 ml, 5.91 mmol) was added over 20 s. The cooling bath was removed, the flask was sealed, and the mixture was stirred overnight for 15 h. An additional portion of TFAA (0.3 mL) was added, and the mixture was stirred for 5 h. The mixture was carefully quenched with saturated aq. sodium bicarbonate solution (50 mL), then diluted with water and extracted with DCM (3×). The cloudy organic layer was stirred over sodium sulfate for 2 min, which resulted in the formation of an orange solution. The mixture was filtered, and the filtrate was concentrated under a vacuum. The residue was dissolved in DCM (5 mL) to give an orange solution. Phosphoryl tribromide (1.693 g, 5.91 mmol) was added in one portion, and the mixture was stirred further at room temperature. After 1 h, the mixture was poured into ice, then diluted with water and DCM. When it had achieved room temperature, the layers were separated. The aq. layer was extracted with DCM (2×), and the combined organic extracts were dried over sodium sulfate, filtered, and concentrated. The aq. layer was further diluted with water and extracted with DCM (2×). The combined organic extracts were dried over sodium sulfate, filtered, and concentrated with residue from the first organic extraction. The combined residue was purified by chromatography on silica gel (40-g Redi-Sep Gold column, 25-g loading column, 0-40% EtOAc/Heptane) to give perfluorophenyl 1-bromo-3-chloroisoquinoline-6-sulfonate (0.482 g, 0.986 mmol, 33.4% yield) as a white solid: m/z (ESI) 488.0 (M+H)+.

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