1,1'-Carbonyldiimidazole → (S)-3-(6-Methyl-2-oxo-2,3-dihydro-benzimidazol-1-yl)-5-phenyl-pentanoic acid ethyl ester

To a solution of (S)-3-(2-Amino-5-methyl-phenylamino)-5-phenyl-pentanoic acid ethyl ester (0.84 g, 2.6 mmol) in THF (15 mL) was added CDI (0.50 g, 3.1 mmol). The reaction mixture was stirred at room temperature for 16 h. When the reaction was complete, the reaction mixture was diluted with CH2Cl2 and washed with water. The organic phase was dried over Na2SO4 and concentrated to afford 0.75 g of the desired product as a dark brown solid. The resulting residue was used for the next reaction without further purification.