3.2.4. Synthesis Method of Intermediate IV

Under nitrogen protection, Dry intermediates III was added to the phosphorus oxychloride, reflux, under 110 ◦C for about 12 h of reaction. After the reaction is cooled to room temperature, phosphorus oxychloride was removed on the rotary evaporator. Then, ice water was added to the residue, the pH was adjusted to 9.0 with sodium bicarbonate, and the temperature during the period did not exceed 40 ◦C. The organic phase was extracted with dichloromethane, and the crude product was concentrated on a rotary evaporator. The crude product was first purified by silica gel column chromatography with the eluent of petroleum ether/ethyl acetate (2/1) to remove other impurities and, then, purified with the eluent of dichloromethane/methanol (40/1) to obtain orange–red product Intermediate **IV**.

#### 8,11-dichloro-5-methyl-5H-indolo[2,3-b]quinoline (Intermediate IV)

Yield, 64%; white solid, m.p. 227–229 ◦C (DMSO); 1H NMR (400 MHz, Chloroform-*d*) *δ* 8.29 (d, *J* = 8.2 Hz, 1H), 8.11 (d, *J* = 8.2 Hz, 1H), 7.75 (t, *J* = 7.8 Hz, 1H), 7.61 (d, *J* = 8.6 Hz, 1H), 7.52 (d, *J* = 1.8 Hz, 1H), 7.46 (t, *J* = 7.6 Hz, 1H), 7.07 (d, *J* = 8.2 Hz, 1H), 4.21 (s, 3H). 13C NMR (100 MHz, Chloroform-*d*) *δ* 155.82, 155.77, 136.71, 136.06, 135.13, 131.24, 125.94, 124.16, 123.75, 122.53, 122.01, 120.23, 119.06, 117.64, 114.31, 33.17. MS-ESI *m*/*z*: calcd for C16H10Cl2N2 [M + H]+: 301.0221; found: 301.1502.
