Combine and cool to 0° C. a solution of (S)-4-benzyl-2-(2-oxo-ethyl)-piperazine-1-carboxylic acid tert-butyl ester (1.95 g, 6.13 mmol) and diethyl benzyl phosphonate (4.23 g, 18.55 mmol) in dry DMF (25 mL), and add solid sodium methoxide (95%, 1.15 g, 21.3 mmol) in a single portion, and stir at 0° C. for 30 minutes. Dilute the mixture with CH2Cl2, wash with brine and dry the organic layer over Na2SO4. Purification by silica gel chromatography of the crude product using EtOAC/CH2Cl2 (2% to 10%) as eluent gives the title compound (2.37 g) as a white solid: mass spectrum (Electrospray): m/z=393.3 (M+1); 1H NMR (400 MHz, CDCl3): δ7.37–7.21 (m, 10H), 6.34–6.30 (m, 1H), 6.12–6.02 (m, 1H), 4.10 (br, 1H), 3.87 (br, 1H), 3.59–3.52 (m, 1H), 3.41–3.35 (m, 1H), 3.13 (m, 1H), 2.82–2.59 (m, 4H), 2.18–2.04 (m, 2H), 1.39 (s, 9H).
