Under an atmosphere of argon, 2,6-difluorobenzoyl chloride (32 mg, 0.2 mmol) was added to a stirred solution of 4 (24 mg, 0.1 mmol) and Hünig's base (95 μL, 70 mg, 0.5 mmol) in dichloromethane (1.0 mL) at room temperature. The reaction was stirred for 0.5 h. The solution was diluted with tetrahydrofuran (0.6 mL), methanol (0.4 mL) and 2 M sodium hydroxide solution (0.2 mL). The mixture was stirred and heated to 60° C. for 15 min then cooled to room temperature, diluted with dichloromethane (5 mL), dried with sodium sulfate and concentrated under reduced pressure. Flash chromatography (ISCO system, silica, 0-25% ethyl acetate in hexane) provided 5 (27.8 mg, 76%) as a solid: LRESIMS m/z 405.1 [M+H]+, calcd. for C20H13F4N2O3 405.1.
