General procedure for the synthesis of 1-(4-nitrophenyl)piperidine from hexahydropyridine and 4-chloronitrobenzene: 4-chloronitrobenzene (100 mg, 0.63 mmol), piperidine (63.86 mg, 0.75 mmol), and SS-Pd (284.5 mg containing 0.01 mmol Pd) were placed in a round-bottomed flask and DMF was added as a solvent. The reaction mixture was heated at 80 °C with magnetic stirring for 6 h. The reaction process was monitored by thin layer chromatography (TLC). After completion of the reaction, the mixture was cooled to room temperature, diluted with water and extracted three times with ethyl acetate. The organic layers were combined and concentrated to obtain the crude product. The crude product was purified by silica gel column chromatography (eluent: hexane/ethyl acetate = 90:10) to afford 1-(4-nitrophenyl)piperidine (22) as a pale yellow solid (112 mg, 86% yield) with a melting point of 104-105 °C. 1H NMR (300 MHz, CDCl3) δ 8.05-8.09 (m, 2H), 6.76-6.79 (m 2H), 3.43 (m, 4H), 1.68 (m, 6H); 13C NMR (75 MHz, CDCl3) δ 155.28, 137.70, 126.27 (2C), 112.20 (2C), 48.72 (2C), 25.66 (2C), 24.61; high-resolution mass spectrometry (HRMS-ESI) calculated values [M+ H]+ C11H15N2O2 207.2490, measured value 207.2472.
