Water → 2-(5-Bromo-2-trifluoromethoxyphenyl)cyclopentane-1,3-dione

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To a solution of 5-bromo-2-trifluoromethoxybenzaldehyde (2.0 g, 7.43 mmol) in anhydrous dichloromethane (40 ml) at room temperature is added boron trifluoride etherate (1.13 ml, 8.92 mmol) then 1,2-bis(trimethylsiloxy)cyclobutene (2.86 ml, 11.2 mmol). The mixture is stirred at room temperature for 23 hours, followed by addition of distilled water (1.2 ml) and additional boron trifluoride etherate (14.1 ml, 112 mmol). After stirring for 24 hours at room temperature the reaction mixture is then quenched with saturated aqueous ammonium chloride solution (50 ml) and extracted with dichloromethane (2×50 ml). The crude product is extracted into 0.5 M aqueous potassium carbonate solution (×3), then the aqueous phase is acidified to pH 1 with concentrated hydrochloric acid. Final extraction with dichloromethane (×3) is followed by washing with brine then drying over magnesium sulfate. Filtration then concentration in vacuo gives a crude product which is purified by preparative reverse phase HPLC to afford 2-(5-bromo-2-trifluoromethoxyphenyl)cyclopentane-1,3-dione.

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