Synthesis
5-Fluoro-1H-indole-3-carboxaldehyde (3.2 g, 19.6 mmol) was used as raw material and dissolved in 10 mL of anhydrous tetrahydrofuran. Subsequently, lithium aluminum hydride (2.61 g, 68.6 mmol) was added to this solution. The reaction mixture was stirred at 70 °C for 2 hours. Upon completion of the reaction, the mixture was cooled to room temperature and the reaction was quenched with 18 mL of 20% sodium hydroxide aqueous solution. The mixture was extracted by adding 60 mL of dichloromethane to the mixture and the organic layer was washed with 40 mL of saturated aqueous sodium chloride solution. The organic phase was dried over anhydrous sodium sulfate and filtered, and the filtrate was concentrated under reduced pressure. The residue was purified by silica gel column chromatography with petroleum ether/ethyl acetate (V/V=50/1) as eluent to afford 5-fluoro-3-methylindole as a light yellow solid (2.41 g, 82.3% yield). The structure of the compound was confirmed by the following spectral data: mass spectrum (ESI, positive ion mode) m/z: 150.2 [M+H]+; 1H NMR (400 MHz, CDCl3) δ: 7.30-7.23 (m, 2H), 7.04 (s, 1H), 6.97 (td, J=9.0,2.0 Hz, 1H), 2.33 (s, 3H).
References
[1] Patent: WO2015/90233, 2015, A1. Location in patent: Paragraph 00362
[2] Angewandte Chemie - International Edition, 2013, vol. 52, # 11, p. 3250 - 3254
[3] Angew. Chem., 2013, vol. 125, # 11, p. 3332 - 3336,5
[4] Organic Letters, 2015, vol. 17, # 11, p. 2652 - 2655
