5-Bromo-4-fluoro-2-(2-fluoro-4-methoxyphenoxy)benzoic acid → 2-bromo-3,5-difluoro-7-methoxy-9H-xanthen-9-one

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Reaction Conditions

Reaction Steps

To a flaske charged with polyphosphoric acid (396 g, 4038 mmol) was added 5-bromo-4-fluoro-2-(2-fluoro-4-methoxyphenoxy)benzoic acid (58 g, 162 mmol) and the viscous mixture was heated at 140° C. for 2 hours. The viscous solution was cooled slightly and diluted with ice-water (1 L). After 15 min of stirring, EtOAc (1 L) was added and the aqueous fraction extracted with EtOAc (3×200 mL). The combined organic fractions were dried over sodium sulfate and concentrated. The solids were washed with 6 N NaOH, then water. The solids were then sequentially triturated with methanol and ethyl acetate. The resulting solid was dried under vacuum to afford 2-bromo-3,5-difluoro-7-methoxy-9H-xanthen-9-one (41 g, 120 mmol, 74.4% yield).

Provenance & Evidence