Another batch was prepared as follows: To a suspension of (6-chloro-3-cyano-pyridin-2-yl)-acetic acid 4-nitro-phenyl ester (157 mg, 0.5 mmol) and sodium percarbonate (157 mg, 1.0 mmol) in anhydrous acetonitrile (4 mL), cooled in an ice-water bath, was added trifluoromethanesulfonic anhydride dropwise (253 μL, 1.5 mmol). The reaction mixture turned into a translucent light yellow solution. After stirring for 3 hrs in ice-water bath, the reaction mixture was poured into saturated sodium carbonate solution (30 mL) and cooled in an ice-water bath. The reaction vial was rinsed with DCM and poured into the sodium carbonate solution. After stirring for 25 min in the ice-water bath, the organic layer was separated. The aqueous layer was further extracted with DCM (2×15 mL). The combined organic layers were dried over anhydrous sodium sulfate. After rotary evaporation of most solvent, the concentrated solution was loaded on a preparative silica TLC (2 mm, 20×20 cm) and developed with EtOAc/Hexane (1:1). The title compound was obtained as a light yellow solid (108 mg, 65%). 1H-NMR (300 MHz, CDCl3) δ 8.29 (d, 2H), 7.68 (d, 1H), 7.51 (d, 1H), 7.31 (d, 2H), 4.40 (d, 2H).
