Synthesis
1. 6-Quinolinecarboxylic acid (9.50 g, 54.9 mmol) was dissolved in ethanol (250 ml), concentrated sulfuric acid (2 ml) was added and the reaction was carried out at reflux for 8 hours. After completion of the reaction, the solvent was removed by evaporation. The residue was dissolved in water and the pH was adjusted to 8 with aqueous potassium hydroxide, the product was collected by filtration and dried under vacuum to give ethyl 6-quinolinecarboxylate (9.85 g, 89% yield) as a light brown solid. Melting point: 66-67 ° C. TLC (unfolding agent: CH2Cl2/MeOH/AcOH = 9:0.5:0.1): Rf = 0.52.
2. Ethyl 6-quinolinecarboxylate (9.80 g, 48.7 mmol) was dissolved in an appropriate amount of solvent and the pH was adjusted to 2 with aqueous 1 N HCl. 20% Pd-Mohr catalyst (1.96 g) was added and hydrogenated at 60 °C and 3 bar hydrogen pressure for 17 h. The reaction was carried out over a 2.5 mmol glass tube. Upon completion of the reaction, the reaction mixture was filtered through diatomaceous earth. The filtrate was evaporated and the residue was dissolved in ethyl acetate and water and the pH was adjusted to 16 with 1N aqueous potassium hydroxide. the organic and aqueous phases were separated, the organic phase was washed with brine, dried over anhydrous Na2SO4 and the solvent was evaporated to give ethyl 1,2,3,4-tetrahydro-6-quinolinecarboxylate (8.72 g, 87% yield) as a light brown solid. Melting point: 68-70°C. GC-MS: [M+]=205.
References
[1] Patent: US2003/232868, 2003, A1. Location in patent: Page 15-16
[2] Patent: US2012/108619, 2012, A1. Location in patent: Page/Page column 36
[3] Patent: WO2007/89626, 2007, A2. Location in patent: Page/Page column 75-76
[4] Chemische Berichte, 1909, vol. 42, p. 4854
[5] Journal of the Chemical Society, 1948, p. 2008,2010
