To a solution of N-[[1-[(2,5-dimethylphenyl)acetyl]-4-piperidinyl]carbonyl]-DL-serine methyl ester (i.e. the product of Example 9, Step C) (2.59 g, 6.88 mmol) in 25 mL of dry acetonitrile and 7 mL of dry dichloromethane was added triphenylphosphine (2.71 g, 10.32 mmol) and then N,N-diisopropylethylamine (1.6 g, 12.38 mmol). The reaction mixture was stirred until homogeneous, and carbon tetrachloride (1.59 g, 10.32 mmol) was added dropwise over 5 minutes. The reaction mixture was stirred for 2.5 h at room temperature, cooled to 0° C. and diluted with 50 mL of ethyl acetate followed by 15 mL of saturated aqueous sodium bicarbonate solution. The mixture was stirred for 10 minutes, poured into 40 mL of water, and the organic layer was separated, washed with brine, dried over MgSO4 and concentrated under reduced pressure to give 6 g of a yellow oil. The oil was purified by flash chromatography on silica gel using 50-100% of ethyl acetate in hexanes to give 900 mg of the title compound. 360 mg of starting amide was also recovered from the reaction mixture.
