To a solution of triphenyl(4-phenylbutyl)phosphonium iodide (975 mg, 1.87 mmol) in THF (8 mL) under Ar at −78° C. was added HMPA (1 mL) followed by n-BuLi (1.6 M in hexane; 1.28 mL, 2.05 mmol, 1.1 equiv.). After stirring at room temperature for 2 h, the mixture was cooled to −78° C. again, and tert-butyl 4-oxopiperidine-1-carboxylate (409 mg, 2.05 mmol, 1.1 equiv.) in THF (2 mL) was added. The mixture was allowed to warm to room temperature and to stand for 2 days. The reaction was quenched with H2O, and the mixture was extracted three times with EtOAc. The combined organic layers were washed with brine and dried over Na2SO4. After concentration, the residue was purified by CC (SiO2, hexane/EtOAc 10:1) to obtain 1-(tert-butoxycarbonyl)-4-(4-phenylbutylidene)piperidine (216 mg, 37%) as a pale yellow oil. 1H NMR (CDCl3, 400 MHz) δ 7.25 (m, 2H), 7.15 (m, 3H), 5.22 (t, 1H, J=7.2 Hz), 3.55 (m, 4H), 2.60 (t, 2H, J=8.0 Hz), 2.15 (m, 4H), 2.03 (m, 2H), 1.66 (m, 2H), 1.46 (s, 9H).
