A suspension of potassium tert-butoxide (1.25 g, 11.1 mmol) and methyltriphenylphosphonium bromide (3.86 g, 1.1 mmol) in tetrahydrofuran (100 mL) was stirred at 40° C. for 30 minutes. The mixture was then cooled to room temperature and a solution of tert-butyl 4-oxo-2-phenylpiperidine-1-carboxylate (2.35 g, 8.5 mmol) in tetrahydrofuran (30 mL) was added slowly. The reaction mixture was stirred at 40° C. for 24 hours. The mixture was cooled to room temperature and quenched by the addition of water and diluted with ethyl acetate (250 mL), The organic layer was separated then washed with water, 10% aqueous citric acid and brine, dried over anhydrous sodium sulfate, filtered and concentrated. Column chromatography on silica gel (hexane:ethyl acetate 95:5 to 9:1) provided tert-butyl 4-methylene-2-phenylpiperidine-1-carboxylate (2.24 g, 96%). 1H NMR (400 MHz, CDCl3): 7.31 (m, 4H), 7.21 (m, 1H), 5.48 (br d, 1H), 4.84 (dd, 2H), 4.07 (br dd, 1H), 2.85 (br, t, 1H), 2.78 (dtr, 1H), 2.64 (dd, 1H), 2.28 (dtr, 1H), 2.20 (br d, 1H), 1.42 (s, 9H). GC/MS (EI) for C17H23NO2: 273 (M+).
