E1. Synthesis of 5-ethoxyindole: Commercially available 5-hydroxyindole (18 g, 13.5 mmol), anhydrous K2CO3 (93.5 g, 5 eq.), and ethyl iodide (40.5 mL, 3.75 eq.) were dissolved in acetone (180 mL) and the reaction was stirred at 50 °C under argon protection. The progress of the reaction was monitored by thin layer chromatography (TLC, spreading agent dichloromethane:methanol=95:5) until the 5-hydroxyindole completely disappeared (about 4 days). After completion of the reaction, the mixture was filtered, the solids were washed with acetone, the filtrates were combined and concentrated to give 17.67 g (90% yield) of the target product 5-ethoxyindole, which was pure enough to be used directly in the subsequent reaction. Melting point: 144-146°C (ethanol recrystallization).
