Trifluoroacetic acid → ethyl 6-[(ethoxycarbonyl)amino]-1,3,4,4a,5,9b-hexahydro-2H-pyrido[4,3-b]indole-2-carboxylate

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Reaction Steps

To a solution of ethyl 6-[(ethoxycarbonyl)amino]-1,3,4,5-tetrahydro-2H-pyrido[4,3-b] indole-2-carboxylate (4.5 g, 13.6 mmol) in CH2Cl2 (40 mL) at 0° C. was added TFA (20 mL) followed by NaCNBH3 (1.8 g, 27 mmol) and stirred at rt for 3 hours before the solvent was removed by the nitrogen stream. To the resulting residue were added CH2Cl2 (40 mL) and 6N HCl (20 mL) and stirred for 0.5 hour. The solution was diluted with water (20 mL), 1N NaOH (30 mL) and extracted with CH2Cl2 (2×30 mL). The combined extracts were dried over magnesium sulfate, concentrated, and purified by flash chromatography to afford ethyl 6-[(ethoxycarbonyl)amino]-1,3,4,4a,5,9b-hexahydro-2H-pyrido[4,3-b]indole-2-carboxylate (3.6 g, 80%) as a clear oil. MS [M+H]+334. 1H NMR (CDCl3, 300 MHz): δ 6.97 (d, 1H, J=7.3 Hz), 6.85 (d, 1H, J=7.3 Hz), 6.72 (t, 1H, J=7.3 Hz), 4.05 (m, 4H), 3.41 (m, 4H), 1.92 (m, 2H), 1.20-1.24 (m, 6H) ppm.

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