To a suspension of phosphonium bromide 78NLS66 (4.69 g, 10.1 mmol) in THF (100 mL) n-butyllithium (1.6 M in hexane, 6.3 mL, 10.1 mmol) was added at 0° C., giving a deep red solution. After stirring for 1 h at rt, a solution of benzyl 4-oxo-1-piperidinecarboxylate (2.24 g, 9.6 mmol) in THF (10 mL) was added dropwise over 30 min. The mixture was stirred at rt for 20 h, then water was added and the mixture extracted three times with diethylether. The combined organic layers were dried over Na2SO4, filtered and concentrated in vacuo. Purification of the residue by silica gel column chromatography, eluting with a stepwise gradient of 0-10% ethyl acetate in n-heptane, afforded the title compound (0.56 g, 17%) as a colourless oil.
