To a solution of 4-[4-(4-ethyl-5-fluoro-2-hydroxyphenoxy)-3-fluorobenzoyl]piperazin-2-one (20 mg, 0.053 mmol; which may be prepared as described in D3) in acetonitrile (550 μL) was added KOH (3 mg, 0.053 mmol) followed by ethylchlorocarbonate (6 μL, 0.058 mmol). After 1 hour at room temperature, the mixture was quenched with water. The aqueous layer was extracted twice with ethyl acetate. The organic phase was dried over sodium sulphate, filtered and concentrated under vacuum. The residue was purified by preparative thin layer chromatography on silica gel, using dichloromethane/methanol (95:5) as eluent. The title product was obtained as a white solid (11 mg, 46%).
