To a solution of 3-(2,4-diphenylamino-pyrimidin-5-yl)-2-(3,4-dimethoxy-phenyl)-propionic acid ethyl ester (470 mg, 0.94 mmol) (from Example 11b supra) in glacial acetic acid (3 mL) was added concentrated sulfuric acid (0.1 mL) in one portion. The reaction mixture was heated at 80° C. overnight. After cooling, the reaction mixture was diluted with ethyl acetate (50 mL) and quenched with 2 N aqueous sodium hydroxide solution. The organic layer was separated and successively washed with water (10 mL) and brine (10 mL), dried over anhydrous sodium sulfate, filtered, and concentrated in vacuo to give the crude product which was crystallized from ethyl acetate-hexanes to give 6-(3,4-dimethoxy-phenyl)-8-phenyl-2-phenylamino-5,8-dihydro-6H-pyrido[2,3-d]pyrimidin-7-one as a light brown solid. (Yield 335 mg, 78.8%).
