**3. Materials and Methods**

#### *3.1. Reagents*

All chemical reagents and solvents were of reagent grade or purified according to standard methods before use. The 1H NMR and 13C NMR spectra were recorded using JNM-ECS-400 MHz and 100 MHz. Mass spectrometry was performed using a Bruker Micro TOF ESI-TOF mass spectrometer. During the experiment, all pH values were measured by PH-10C pH meter. The purity of the synthesized derivatives was characterized by a purity test (as shown in Figures S1–S42).

#### *3.2. Synthesis*

3.2.1. Synthesis Method of Intermediate I

The indole (10.88 mmol) was added to the mixture of pyridine (14.2 mmol) and tetrahydrofuran (40 mL) at 0 ◦C, and the reaction was stirred at 0 ◦C for 0.5 h. Then, the mixed solution of trichloroacetyl chloride (14.2 mmol) and tetrahydrofuran (30 mL) was added slowly. After the reaction was raised to room temperature and stirred continuously for 16 h, 10% HCl solution was added to the reaction system at 0 ◦C, and the organic phase was extracted with ethyl acetate (300 mL), washed with salt water, and dried with anhydrous magnesium sulfate. The solvent was removed on the rotary evaporator, and the solid product was directly dissolved in anhydrous methanol (150 mL). Then, 10% KOH solution (20 mL) was added, the reaction mixture was heated and reflux for 5 h, and, then, concentrated in the rotary evaporator, the solvent was removed, and the large solid product was extracted with ethyl acetate (200 mL). The organic phase was washed with salt water, dried with anhydrous magnesium sulfate, and the solvent was removed. The crude product was purified by silica gel column chromatography with the eluent of n-hexane/ethyl acetate (4/1). Finally, Intermediate I was obtained.

Methyl 6-chloro-1H-indole-3-carboxylate (Intermediate I)

Yield, 85%; white solid, m.p. 182–185 ◦C (DMSO); 1H NMR (400 MHz, DMSO-*d*6) *δ* 12.05 (s, 1H), 8.14 (d, *J* = 3.0 Hz, 1H), 7.99 (d, *J* = 8.5 Hz, 1H), 7.55 (d, *J* = 2.0 Hz, 1H), 7.22 (d, *J* = 8.5 Hz, 1H), 3.82 (s, 3H). 13C NMR (100 MHz, DMSO-*d*6) *δ* 164.89, 137.24, 133.90, 127.51, 124.86, 122.20, 122.09, 112.51, 107.03, 51.25. MS-ESI *m*/*z*: calcd for C10H8ClN2O[M + H]+: 210.0244; found: 210.1683.
