5-(Methoxycarbonyl)pentanoyl chloride (2.82 g, 0.017 mol) and triethylamine (3.47 g, 0.034 mol) were added to a solution of 2-(3,4-dichlorophenyl)-2-hydroxy-1-[phenyl]ethanone (Step 1) (4.77 g, 0.017 mmol) in 40 mL of methylene chloride. The resulting mixture was stirred overnight at room temperature. The reaction mixture was diluted with 100 mL of methylene chloride. The organic solution was washed with water (1×100 mL), saturated brine (1×100 mL), dried over magnesium sulfate, filtered and concentrated. The concentrated residue was dried under high vacuum, then ammonium acetate (4.6 g, 0.06 mol) and 30 mL of acetic acid were added. The reaction mixture was heated at 100° C. for 2.5 h. The reaction mixture was cooled to room temperature, and the excess acetic acid was removed under vacuum. The resulting residue was partitioned between water (100 mL) and ethyl acetate (200 mL). The organic layer was separated, washed with saturated aqueous sodium bicarbonate (2×100 mL), saturated brine (1×100 mL), dried over magnesium sulfate, filtered and concentrated. The concentrated residue was purified by flash chromatography on silica gel (eluting with 1:9 ethyl acetate:hexane) to give 2.82 g (42.6%) of methyl [(4-phenyl)-5-(3,4-dichlorophenyl)oxazole]-2-butanoate as a yellow oil: HRMS calcd. for C20H17N1O3Cl2 390.0664. Found 390.0648.
