To a stirred solution of 3-acetyl-4-(2-isopropylphenyl)-6-methyl-1-ethoxycarbonylmethyl-2-pyridinone from step 3 above (0.65 g, 1.8 mmol) in CH2Cl2 (150 mL) at 0° C. was added 30% aqueous H2O2 (0.94 mL, 9 mmol) and trifluoroacetic anhydride (1.8 mL, 14 mmol). The resulting solution was refluxed for 1 h and then diluted with CH2Cl2 and water. The organic phase was separated, dried over Na2SO4, filtered, and concentrated in vacuo to give the title compound (0.325 g; NMR: OCOCH3 peak at 2.05 ppm; HPLC RT=22.81 min, method B).
