6 N NaOH solution (6 mL), (Bu4N)2SO4 (50% wt. solution in H2O, 0.20 mL), and TsCl (646 mg, 3.39 mmol) were added to a suspension of tert-butyl 7-bromo-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxylate (991 mg, 2.82 mmol) in toluene (20 mL) and the resulting suspension was stirred at 25° C. for 1.5 h. H2O and EtOAc were added to the suspension and the phases were separated. The organic phase was washed with H2O, dried over Na2SO4 and concentrated under reduced pressure to afford the title compound (1.285 g, 90%) as a white foam: 1H NMR (300 MHz, CDCl3) δ 8.32 (d, J=1.5 Hz, 1H), 7.78-7.66 (m, 2H), 7.36 (dd, J=8.4, 1.5 Hz, 1H), 7.25-7.21 (m, 2H), 7.21-7.13 (m, 1H), 4.92-4.81 (m, 2H), 3.74-3.63 (m, 2H), 2.70-2.61 (m, 2H), 2.37 (s, 3H), 1.50 (s, 9H).
