A solution of 3-(5-Amino-3H-isobenzofuran-1-ylidene)-5-chloro-1,3-dihydro-indol-2-one (75 mg, 0.251 mmol), trityl chloride (84 mg, 0.301 mmol) and triethylamine (53 μμl, 0.377 mmol) in DMF (2.0 ml) was stirred at room temperature for 1.25 hours. The mixture was partitioned between EtOAc and water. The EtOAc layer was washed with brine, dried with Na2SO4 and rotary evaporated. The yellow solid was precipitated from CHCl3 to give 5-chloro-3-[5-(trityl-amino)-3H-isobenzofuran-1-ylidene]-1,3-dihydro-indol-2-one as a bright yellow solid (61 mg, 45%).
