The reaction mixture was stirred overnight at room temperature in acetonitrile (8 mL) with 4-bromo-2,3-dihydro-1H-indole (759 mg, 3.81 mmol) and di-tert-butyl dicarbonate (976 mg, 4.48 mmol). After completion of the reaction, the solvent was removed by rotary evaporation and the residue was dissolved in ethyl acetate (40 mL). The organic layer was washed sequentially with water (3 x 20 mL) and saturated saline (1 x 20 mL). The organic phase was collected, dried over anhydrous sodium sulfate and concentrated under reduced pressure. Finally, it was purified by silica gel column chromatography (eluent: petroleum ether) to afford N-Boc-4-bromoindoline (840 mg, 74% yield) as a white solid.1H NMR (400 MHz, DMSO-d6) δ 1.50 (s, 9H), 3.02 (t, J = 8.8 Hz, 2H), 3.94 (t, J = 8.8 Hz, 2H) 7.12 (m, 2H), 7.56 (m, 1H).
