120-72-9

26340-49-8

General procedure for the synthesis of 2-iodoindole from indole: n-butyllithium (nBuLi, 17 mL, 2.62 M hexane solution, 44.54 mmol) was slowly added to a tetrahydrofuran (THF, 80 mL) solution of indole (5.00 g, 42.68 mmol) at -78 °C. The resulting white suspension was stirred at -78 °C for 0.5 h and then bubbled through carbon dioxide (CO2, gas) for 10 min. The solvent was evaporated at 0 °C (~20 lHPa), the crystalline residue was dissolved in THF (100 mL) and cooled to -78 °C, and tert-butyllithium (tBuLi, 31 mL, 1.46 M pentane solution, 45.26 mmol) was added dropwise. After stirring at -78 °C for 1 h, a THF (80 mL) solution of 1,2-diiodoethane (14.40 g, 51.09 mmol) was added dropwise. Stirring was continued at -78 °C for 1 h. Water (H2O, 5 mL) was then added dropwise and the reaction mixture was slowly warmed to room temperature. The reaction was quenched with saturated aqueous ammonium chloride (NH4Cl, 50 mL). The organic and aqueous layers were separated and the aqueous layer was extracted with ethyl acetate (AcOEt, 2 x 80 mL). The organic layers were combined and washed sequentially with 20% sodium thiosulfate (Na2S2O3, 80 mL) aqueous solution, brine (80 mL), dried with anhydrous magnesium sulfate (MgSO4) and concentrated under reduced pressure. The residue was purified by recrystallization from hexane/dichloromethane (70:1, 40 mL) to afford 2-iodoindole (7.62 g, 74% yield) as white crystals. The filtrate was concentrated under reduced pressure and the residue was purified by recrystallization from hexane/dichloromethane (70:1, 10 mL) to afford 2-iodoindole (0.56 g, 5% yield) as white crystals. The filtrate was again concentrated under reduced pressure and the residue was purified by recrystallization from hexane/dichloromethane (70:1, 8 mL) to afford 2-iodoindole (0.27 g, 3% yield) as light purple crystals. Finally, the filtrate was concentrated under reduced pressure and the residue was purified by fast chromatography (silica gel, hexane/ethyl acetate = 35:1) to afford 2-iodoindole (0.42 g, 4% yield) as white crystals.The total yield of 2-iodoindole was 86%.