Diethyl Ether → trifluoro-methanesulfonic acid 2-morpholin-4-yl-4-oxo-4H-chromen-8-yl ester

Trifluoro-methanesulfonic acid 2-hydroxy-3-(3-morpholin-4-yl-3-oxo-propionyl)-phenyl ester [D] (1.06 g, 2.7 mmol) in dichloromethane (30 ml) was treated with trifluoromethanesulphonic anhydride and stirred over night at room temperature. The reaction mixture was then concentrated, re-dissolved in methanol and stirred for a further 2 hours. The solution was diluted with water and basified to pH8. It was then extracted three times with dichloromethane. The extracts were combined, washed with brine, dried with magnesium sulphate and evaporated to give the crude product as a brown oil. Trituration with ether gave trifluoro-methanesulfonic acid 2-morpholin-4-yl-4-oxo-4H-chromen-8-yl ester [E] as a brown solid. Yield 210 mg, 20%.