3.2.27. Tert-butyl 4-((2-nitrophenyl)amino)piperidine-1-carboxylate (56)

1-fluoro-2-nitrobenzene (0.756 mL, 7.08 mmol) was dissolved in a stirred solution of tert-butyl 4-aminopiperidine-1-carboxylate (1.99 g, 9.92 mmol) and a suspension of fine-powdered K₂CO₃ (2.16 g, 15.6 mmol) in dry DMF (5 mL) under nitrogen gas. The reaction mixture was kept at 70 °C overnight. The mixture was concentrated under reduced pressure. Brine (20 mL) was added, and the product was extracted with EtOAc. The combined organic phases were washed with brine (15 mL), dried (Na₂SO₄) and concentrated under reduced pressure. The crude product was purified by silica gel chromatography (PE/EtOAc 9:1 to PE/EtOAc/MeOH 8.5:1:0.5) to give 56 (2.20 g, 96%) as an orange solid.