A suspension of triphenylphosphine (9.49 g, 36.18 mmol), iodine (7.98 g, 31.44 mmol) and triethylamine (8.49 ml, 60.75 mmol) in tetrahydrofuran was cooled to −78° C. then treated with tert-butyl (3R)-6-cyclohexyl-3-({[1-(methoxycarbonyl)-2-oxopropyl]amino}carbonyl)hexanoate (Preparation 172) (4.86 g, 11.80 mmol) over 15 minutes. The mixture was stirred at −78° C. for 30 minutes then at 0-5° C. for 2 hours. The mixture was diluted with water and extracted with dichloromethane. The combined organic layers were dried over anhydrous magnesium sulphate, filtered and the solvent removed under reduced pressure. The residue was purified by column chromatography on silica gel eluting with a gradient system of ethyl acetate:pentane (0:100 to 10:90) to afford the title compound as a colourless oil (2.92 g).
