Synthesis of spiro[indene-2,1’-isoindoline]-1,3,3’-trione (5)
i) 2’-(5-Methoxyquinolin-8-yl)spiro[indene-2,1’-isoindoline]- 1,3,3’-trione (3s , 84 mg, 0.2 mmol) was placed in a 10 mL two-necked reaction flask, which was filled with nitrogen by using the standard Schlenk technique. DCM (1.0 mL) was sequentially injected via a syringe. To the suspension was added BBr3 (0.24 mL, 1M in THF, 0.24 mmol) at 0 °C (ice-water bath). The mixture was stirred at 0 °C (ice-water bath) for 5 min and then allowed to warm to room temperature for 18 h. The resulting mixture was quenched with water at 0 °C and extracted with ethyl acetate three times. The combined organic layer was washed with water and dried over anhydrous Na2SO4.
ii) The crude product dissolved in MeCN/H2O (MeCN/H2O = 4:1, 2 mL), Ce(NH4)2(NO3)6(CAN, 658 mg, 1.2 mmol) was added to the mixture with a portion at room temperature, and the mixture was stirred for 12 h at 60 °C (oil bath). After the reation completed, H2O (5 mL) was added and the mixture was extracted with ethyl acetate (3 mL ×3). Combined organic phase was dried over anhydrous Na2SO4, filtered through Celite and the filtrate was concentrated. The crude residue was purified by flash chromatography in petroleum ether:ethyl acetate= 1:1 to give 5 as white soild (27 mg, 51%).