General procedure for the synthesis of 5-bromo-1-methyl-2-oxodihydroindole from 1-methyl-2-indolinone: N-methylindole (0.5 g, 3.4 mmol) was dissolved in acetonitrile (5 mL) and stirred at 0 °C. Subsequently, N-bromosuccinimide (NBS, 0.62 g) dissolved in acetonitrile (10 mL) was added slowly and dropwise. The reaction mixture was kept stirred at 0 °C for 1 h, followed by continued stirring for 2 h at room temperature. After completion of the reaction, the solvent was removed by rotary evaporation and the resulting solid was dissolved in chloroform (CHCl3) and washed twice with deionized water. After removing the chloroform again by rotary evaporation, the resulting brown solid was recrystallized with hexane to give 5-bromo-N-methylhydroxyindole (0.44 g, 58% yield). The product was characterized by 1H-NMR (300 MHz, CDCl3) with the following chemical shifts δ (ppm): 7.42-7.39 (d, 1H), 7.26 (s, 1H), 6.71-6.68 (d, 1H), 3.52-3.20 (s, 2H), 3.19 (s, 3H).
