1-Benzoylpiperidine-4-carbaldehyde → 4-(1-Hydroxy-prop-2-enyl)-1-benzoyl piperidine

To a solution of 500 mg of 1-benzoylpiperidine-4-carboxaldehyde (Step C) in 10 mL THF at −78° C., was added 2.99 mmol of vinyl magnesium bromide. The solution was warmed to 0° C. and stirred for 1 h. The reaction was quenched with 15 mL of aq. ammonium chloride and extracted with 3×20 mL ether and the combined organic layers were dried over magnesium sulfate. The solvent was evaporated under reduced pressure and the residue was purified by flash chromatography with 2:1 hexane:ethyl acetate followed by 1:1 hexane:ethyl acetate followed by hexane:ethyl acetate:methanol, 50:50:5 to give 411 mg of the title compound.