Methylmalonic Acid → 1-(2-fluoro-4-iodophenyl)-5-hydroxy-3,6,8-trimethyl-1H,8H-pyrido[2,3-d]pyrimidine-2,4,7-trione

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To a 6:5 mixture (59.6 g) of 1-(2-fluoro-4-iodophenyl)-3-methyl-6-methylamino-1H-pyrimidine-2,4-dione 67 and 3-(2-fluoro-4-iodophenyl)-1-methyl-6-methylamino-1H-pyrimidine-2,4-dione 68 obtained in Step 4 and 2-methyl-malonic acid 54 (20.7 g) was added acetic anhydride (180 ml), and the mixture was stirred with heating at 95° C. for 1 hr. After allowing to cool to room temperature, the mixture was concentrated under reduced pressure. Tetrahydrofuran (350 ml) was added to the residue, and the mixture was stirred with heating under reflux for 1 hr. After allowing to cool to room temperature, the crystals were filtered off. The filtrate was concentrated under reduced pressure and the residue was purified by column chromatography (chloroform:tetrahydrofuran=18:1). Toluene (150 ml) was added to the obtained solid, and the mixture was stirred with heating under reflux for 30 min. After allowing to return to room temperature, the crystals were collected by filtration and dried to give 1-(2-fluoro-4-iodophenyl)-5-hydroxy-3,6,8-trimethyl-1H,8H-pyrido[2,3-d]pyrimidine-2,4,7-trione 69 (27.0 g, yield 37%) as colorless crystals.

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