[Synthesis]
GENERAL STEPS: 3-oxocyclohexanecarboxylic acid (200 mg, 1.407 mmol) was dissolved in acetic acid (3 mL), and a solution of phenylhydrazine (160 mg, 1.480 mmol) in acetic acid (2 mL) was slowly added with stirring at room temperature. The reaction mixture was heated to reflux for 2 hours. After completion of the reaction, the mixture was cooled to room temperature, diluted with ethyl acetate and extracted with brine. The organic layer was separated, dried over anhydrous sodium sulfate and concentrated under reduced pressure to remove the solvent. The crude product was recrystallized by ethyl acetate/hexane to give a light brown microcrystalline solid 2,3,4,9-tetrahydro-1H-carbazole-2-carboxylic acid (191 mg, 63% yield) with a melting point of 235-238 °C (literature values: Asselin et al. J. Med. Chem., 1976, 19, 787-792, melting point 239-241 °C; Allen et al. J. Heterocyclic Chem., 1970, 7, 239-241, melting point 233-235°C). IR (KBr, cm-1): 3416, 3048, 2923, 2844, 1689, 1465, 1444, 1415, 1288, 1264, 1226, 935, 740. 1H NMR (DMSO-d6, δ): 12.27 (1H, s), 10.66 (1H, s), 7.33 (1H, d, J = 7.6 Hz), 7.24 (1H, d, J = 7.6 Hz), 6.98 (1H, dt, J = 1.2 Hz, J = 6.8 Hz), 6.91 (1H, dt, J = 1.2 Hz, J = 6.8 Hz), 2.89-2.62 (5H, m), 2.17 (1H, m), 1.87-1.81 (1H, m). |