Hydrochloric Acid → 3-(2-piperidin-4-yl-phenylsulfanyl)-1H-indole

1.58 g 4-(2-Triisopropylsilanylsulfanyl-phenyl)-piperidine-1-carboxylic acid tert-butyl ester (3.51 mmol) in 10 mL THF was added to 1.21 g tetrabutylammonium fluoride dihydrate (3.85 mmol) in 5 mL THF at 0° C. The reaction mixture was stirred 1 hour at 0° C., filtered through a plug of silica (eluted with EtOAc/heptane 1:1) and concentrated in vacuo. The residue was redissolved in 14 mL THF. 2 mL of this solution (≈0.5 mmol) was added to 67 mg N-chloro succinimide (0.50 mmol) in 2 mL 1,2-dichloro-ethane at 0° C. The reaction mixture was stirred 30 minutes at room temperature. The resulting solution was added to 90 mg indole (0.75 mmol) in 2 mL THF at 0° C. The reaction mixture was stirred 2 hour at 0° C., poured into 20 mL saturated NaHCO3 and extracted with ethyl acetate (2×50 mL). The combined organic phases were washed with brine (20 mL), dried with MgSO4 and concentrated in vacuo. The residue was purified by flash chromatography (silica gel; ethyl acetate/heptane) to give 89 mg 4-[2-(1H-indol-3-ylsulfanyl)-phenyl]-piperidine-1-carboxylic acid tert-butyl ester (0.22 mmol, ≈44%). 2 mL diethyl ether saturated with HCl was added to 4-[2-(1H-indol-3-ylsulfanyl)-phenyl]-piperidine-1-carboxylic acid tert-butyl ester and stirred over night at room temperature. The reaction mixture was neutralized with saturated NaHCO3 and extracted with ethyl acetate (2×50 mL). The combined organic phases were washed with brine (20 mL), dried with MgSO4 and concentrated in vacuo. 3-(2-piperidin-4-yl-phenylsulfanyl)-1H-indole was isolated after preparative HPLC.