To a solution of (S)-benzyl 3-(tert-butoxycarbonylamino)piperidine-1-carboxylate (500 mg, 1.49 mmol) in DMF (5 mL) was added NaH (60% suspension in mineral oil, 120 mg, 1.64 mmol) and the reaction mixture was stirred for 1 h. To the reaction mixture was added ethyl bromide (0.12 mL, 1.64 mmol) and the reaction mixture was stirred for 4 h. The reaction mixture was diluted with ice-cooled water and the solution was extracted with EtOAc, the EtOAc layer was dried over Na2SO4 and concentrated in vacuo to give the crude product that was purified by column chromatography (silica gel, gradient, EtOAc in hexanes) to give (300 mg, 55%) of the titled compound. 1H NMR (400 MHz, CDCl3): δ 7.36-7.30 (m, 5H), 5.18-5.12 (m, 2H), 4.18-4.13 (m, 2H), 3.68-3.62 (m, 1H), 3.22-3.17 (m, 2H), 3.01-2.85 (m, 1H), 2.68-2.59 (m, 1H), 1.89-1.81 (m, 1H), 1.78-1.73 (m, 2H), 1.55 (s, 9H), 1.54-1.48 (m, 1H), 1.08 (t, J=6.4 Hz, 3H). ES-MS: m/z [M+1]=363.
