Hydrochloric Acid → Ethyl 1-(2-Aminoethyl)-4,5,6,7-tetrahydro-1H-indole-2-carboxylate

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Reaction Steps

A 200-mL Parr reactor bottle was purged with nitrogen and charged with 10% palladium on carbon (50% wet, 1.28 g dry weight), 101e (3.00 g, 12.9 mmol), 12% hydrochloric acid (6.5 mL, 25 mmol), ethyl acetate (60 mL) and ethanol (40 mL). The bottle was attached to a Parr hydrogenator, evacuated, charged with hydrogen gas to a pressure of 50 psi and shaken for 6 h. After this time, the hydrogen was evacuated, and nitrogen was charged into the bottle. Diatomaceous earth filtration agent (Celite® 521, 4.0 g) was added, and the mixture was filtered through a pad of Celite 521. The filter cake was washed with ethanol (2×20 mL), and the combined filtrates were concentrated to dryness under reduced pressure. The residue was partitioned between ethyl acetate (150 mL) and 10% aqueous potassium carbonate (100 mL). The organic layer was separated, and the aqueous layer was extracted with ethyl acetate (3×75 mL). The combined organic layers were dried over sodium sulfate and concentrated under reduced pressure. The residue was triturated with ethanol (5 mL) to afford a 71% yield (1.71 g) of ethyl 1-(2-aminoethyl)-4,5,6,7-tetrahydro-1H-indole-2-carboxylate 101f as a white solid: mp 102-104° C.; 1H NMR (500 MHz, DMSO-d6) δ 6.61 (s, 1H), 6.22 (br, 2H), 4.15 (m, 4H), 2.77 (m, 2H), 2.59 (t, 2H, J=6.5 Hz), 2.42 (t, 2H, J=6.5 Hz), 1.70 (m, 2H), 1.62 (m, 2H), 1.23 (t, 3H, J=7.0 Hz); MS (APCI+) m/z 237.2 (M+H)

Provenance & Evidence