To thionyl chloride (60 mL) was added 1-(diphenylmethyl)-3-hydroxy-3-(7-hydroxyquinoxalin-6-yl)-1,3-dihydro-2H-indol-2-one (3.0 g, 6.53 mmol) at −10° C. The resulting reaction mixture was stirred at 0° C. for 1 h, and concentrated in vacuo. The residue was dissolved in acetic acid (150 mL), followed by the addition of zinc dust (4.50 g, 68.81 mmol). The resulting mixture was stirred at ambient temperature for 40 min. The solids were filtered out. The filtrate was concentrated in vacuo. The residue was dissolved in ethyl acetate (200 mL), washed with water and brine, dried over anhydrous sodium sulfate and filtered. The filtrate was concentrated in vacuo, the residue was purified by column chromatography (dichloromethane/methanol 200/1) to give 1-(diphenylmethyl)-3-(7-hydroxyquinoxalin-6-yl)-1,3-dihydro-2H-indol-2-one (2.40 g, 83%): MS (ES+) m/z 444 (M+1).
