Trifluoromethanesulfonic anhydride → Trifluoromethanesulfonic acid 7-chloro-3-(3,5-dimethylphenyl)-6-nitro-2-oxo-1,2-dihydroquinolin-4-yl ester

To a solution of 7-chloro-3-(3,5-dimethylphenyl)-4-hydroxy-6-nitro-1H-quinolin-2-one (1.0 g in 50 mL dry methylene chloride) was added 0.455 ml diazabicycloundecene and the mixture cooled to -78° C. To this was added trifluoromethanesulfonic anhydride (0.51 mL) dropwise via syringe and the mixture stirred at low temperature. After 1 hour, the reaction was quenched by the addition of saturated ammonium chloride (35 mL) and extracted with ethyl acetate (3×75 mL). The organics were washed with water (50 mL) and brine (50 mL) then dried over magnesium sulfate. Purification of the concentrate by flash chromatography on silica gel (hexane:ethyl acetate, 3:2) gave the title compound (629 mg).