Reaction Steps
A heavy-walled Pyrex tube was charged with a solution of 9H-pyrido[3,4-b]indole-1-carbaldehyde, 2, (0.20 g, 1.02 mmol) in 1,2-dichloroethane (5 mL). This solution was treated with tert-butyl 4-(5,6,7,8-tetrahydroquinolin-8-ylamino)butylcarbamate, 3, (0.36 g, 1.12 mmol), sodium triacetoxyborohydride (0.43 g, 2.04 mmol), 4 A molecular sieves and a catalytic amount of acetic acid (2 drops). The reaction mixture was exposed to microwave irradiation for 10 min at a temperature of 100° C. After the irradiation, the reaction mixture was cooled with high-pressure air until the temperature had fallen below 40° C. The crude reaction mixture was poured onto a saturated aqueous solution of sodium bicarbonate. The product was extracted with dichloromethane. The combined organic layers were washed with brine, dried over potassium carbonate, filtered and concentrated in vacuo. The crude product was purified by silica gel chromatography (0-5% methanol/CH2Cl2) to afford 0.12 g (24% yield) of desired product 4: 1H NMR (400 MHz, CDCl3) δ 13.43 (bs, 1H), 8.67 (d, J=3.6 Hz, 1H), 8.24 (d, J=5.6 Hz, 1H), 8.10 (d, J=7.6 Hz, 1H), 7.82 (d, J=5.2 Hz, 1H), 7.69 (d, J=8.4 Hz, 1H), 7.54 (dt, J=1.2, 7.4 Hz, 1H), 7.41 (d, J=7.2 Hz, 1H), 7.21 (dt, J=0.8, 7.2 Hz, 1H), 7.14 (dd, J=4.8, 7.6 Hz, 1H), 4.28-4.02 (m, 4H), 2.90-2.60 (m, 5H), 2.44-2.26 (m, 2H), 2.12-2.04 (m, 1H), 1.96-1.84 (m, 1H), 1.80-1.65 (m, 1H), 1.44-1.25 (m, 1H), 1.33 (s, 9H), 1.22-1.12 (m, 1H); ESI+ MS: m/z (rel intensity) 500.2 (100, [M+H]+).
