Synthesis
(3-2) Ethyl 3-(4-fluoro-2-nitrophenyl)-2-oxopropanoate (5.51 g, 21.6 mmol) obtained in Reference Example (3-1) was dissolved in a mixed solvent of ethanol and acetic acid (1:1, 84 mL, by volume). Iron powder (10.9 g, 144 mmol) was added to this solution and the mixture was subsequently heated to reflux for 3.5 hours. Upon completion of the reaction, the reaction mixture was diluted with tetrahydrofuran and filtered through diatomaceous earth to remove insoluble material. The filtrate was concentrated under reduced pressure and the resulting residue was purified by silica gel column chromatography (eluent: dichloromethane/acetone = 15:1) to afford ethyl 6-fluoro-1H-indole-2-carboxylate (3.62 g, 81% yield). The product was characterized by 1H-NMR (400 MHz, CDCl3): δ 8.89 (1H, br.s), 7.61 (1H, dd, J=8.8,5.5 Hz), 7.20 (1H, m), 7.09 (1H, dd, J=9.4,2.0 Hz), 6.94 (1H, dd, J=9.4,8.8,2.0 Hz). 4.41 (2H, q, J=7.0 Hz), 1.42 (3H, t, J=7.0 Hz).
(9-6) Ethyl 3-(4-fluoro-2-nitrophenyl)-2-oxopropanoate (5.51 g, 21.6 mmol) obtained in Reference Example (9-5) was dissolved in a mixed solvent of ethanol and acetic acid (1:1, 84 mL, by volume). Iron powder (10.9 g, 144 mmol) was added to this solution and the mixture was subsequently heated to reflux for 3.5 hours. Upon completion of the reaction, the reaction mixture was cooled to room temperature and diluted with tetrahydrofuran. Insoluble material was removed by filtration through diatomaceous earth and the filtrate was concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (eluent: dichloromethane/acetone=15:1) to afford ethyl 6-fluoro-1H-indole-2-carboxylate (3.62 g, 81% yield) as yellow crystalline. The product was characterized by 1H-NMR (400 MHz, CDCl3): δ 8.89 (1H, br.s), 7.61 (1H, dd, J=8.8,5.5 Hz), 7.20 (1H, m), 7.09 (1H, dd, J=9.4,2.0 Hz), 6.94 (1H, dd, J=9.4,8.8,2.0 Hz). 4.41 (2H, q, J=7.0Hz), 1.42 (3H, t, J=7.0Hz).
References
[1] Patent: EP1764075, 2007, A1. Location in patent: Page/Page column 81-82; 91
[2] Patent: WO2006/109633, 2006, A1. Location in patent: Page/Page column 138-139
