tert-Butyl (S)-(3-(4-iodophenyl)-1-oxo-1-(piperidin-1-yl)propan-2-yl)carbamate (Compound SP413, Boc-Phe(4-I)-pip) (6.00 g, 13.09 mmol), tert-butyl hex-5-ynoate (Compound SP423) (4.40 g, 26.2 mmol) and triethylamine (5.47 ml, 39.3 mmol) were dissolved in DMF (60.0 ml), CuI (0.125 g, 0.655 mmol) and Pd(dppf)Cl2.CH2Cl2 (0.538 g, 0.655 mmol) were added and the mixture was stirred at room temperature for 4 hours. The reaction solution was diluted with hexane/ethyl acetate (1/1) and washed with a saturated aqueous ammonium chloride solution and brine. The organic layer was dried over anhydrous magnesium sulfate, and then filtered and concentrated under reduced pressure, and the resulting residue was purified by column chromatography (hexane:ethyl acetate=100:0-60:40) to afford the title compound SP425 (6.19 g, 95%).
