Dissolved 15E (1.5 g, 3.82 mmol) in 15 mL of DMF and added EDC (1.28 g, 6.68 mmol) and HOBt (0.88 g, 6.49 mmol). The mixture was stirred for at least 15 minutes. Next, DIEA (2.0 mL, 11.4 mmol) was added along with tert-butyl piperazine-1-carboxylate (0.85 g, 4.58 mmol). This reaction mixture was then stirred overnight at RT. After the disappearance of 15E, this mixture was poured into 150 mL of water. The white solid was filtered, rinsed with water and dried under vacuum to provide tert-butyl 4-(1-((1R,2R)-2-(benzyloxy)cyclohexyl)-2-oxo-5-phenyl-2,3-dihydro-1H-imidazole-4-carbonyl)piperazine-1-carboxylate (15Ga) (1.6 g, 75%). ESI-MS: m/z 561.6 (M+H)+.
