Indole-3-propylamine Condensation Synthesis

p-Toluenesulfonic acid (0.11 g, 0.57 mmol) was added to a flask charged with 3-(1H-indol-3-yl)-propylamine^{15 (link)} (0.10 g, 0.57 mmol) and 5-chloroisatin (0.12 g, 0.63 mmol) in absolute ethanol (5 mL) and heated to 100 °C. After 15 h, the reaction mixture was cooled to room temperature and concentrated in vacuo. The residue was dissolved in ethyl acetate and washed with 0.5 M NaOH and saturated aqueous NaCl. The organic layer was separated and dried over Na₂SO₄, filtered, and concentrated in vacuo. The residue was purified by flash chromatography to provide 6 as an orange solid (17 mg, 9%). ¹H NMR (300 MHz, DMSO-d₆): δ 10.56 (s, 1H), 10.10 (s, 1H), 7.46 (dd, J = 7.0, 1.5 Hz, 1H), 7.32 (dd, J = 8.4, 2.2 Hz, 1H), 7.15 (m, 2H), 7.00 (dd, J = 6.9, 1.5 Hz, 1H), 6.97 (dd, J = 6.9, 1.8 Hz, 1H), 6.93 (d, J = 8.4 Hz, 1H), 3.47 (m, 2H), 3.02 (m, 3H), 1.98 (m, 2H). MS (ESI) m/z 338.0 (M + H)⁺.