[CH2:1]([O:8][C:9]1[CH:10]=[C:11]2[C:15](=[CH:16][CH:17]=1)[NH:14][C:13](=[O:18])[CH2:12]2)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[CH:19](OCC)([O:23][CH2:24][CH3:25])[O:20][CH2:21][CH3:22]>>[CH2:1]([O:8][C:9]1[CH:10]=[C:11]2[C:15](=[CH:16][CH:17]=1)[N:14]([CH:19]([O:23][CH2:24][CH3:25])[O:20][CH2:21][CH3:22])[C:13](=[O:18])[CH2:12]2)[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1A mixture of 5-benzyloxyoxindole (1.88 g, 7.9 mmol), (EP 0636608 A1), and triethyl orthoformate (180 ml) was heated at reflux with stirring for 3 hours. The volatiles were removed by evaporation and the residue was purified by column flash chromatography using petroleum ether/ether (7/3) as eluent. Evaporation of the solvents lead to a crystalline material which was collected by filtration and dried under vacuum to give 5-benzyloxy-1-diethoxymethyloxindole (1.96 g, 73%).
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