A mixture of 1-(2-tert-butylphenyl)piperazine dihydrochloride (Reference Example 1, 2.18 g, 7.50 mmol), 5-(3-tert-butoxy-3-oxopropyl)-1,3-oxazole-4-carboxylic acid (Reference Example 22, 1.90 g, 7.88 mmol), triethylamine (1.52 g, 7.88 mmol), EDCI (1.51 g, 7.88 mmol) and HOBt (1.21 g, 7.88 mmol) in MeCN (40 mL) was stirred at room temperature for 16 h. The reaction mixture was concentrated under reduced pressure, and the resulting residue was partitioned between ethyl acetate and water. The organic layer was washed with 10% NaHCO3, saturated brine, dried over anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. The resulting residue was purified by flash column chromatography (silica gel, 9:1-2:3 hexane/ethyl acetate) to give the title compound (2.81 g) as a light yellow oil.
