A quantity of 0.346 g (1.00 mmol) of 50% to 60% m-chloroperbenzoic acid (assuming 50% peracid was present) was added at 25° C. to a stirred solution of 0.165 g (0.47 mmol) of 6-(2,6-dichlorophenyl)-8-methyl-2-methylsulfanyl-8H-pyrido[2,3-d]pyrimidin-7-one of Example 37 in 15 mL of chloroform, and the solution was stirred overnight. A quantity of 0.25 g (3.20 mmol) of dimethylsulfoxide was added to reduce any excess peracid. After 15 minutes, the chloroform solution was washed with 30 mL of saturated sodium bicarbonate and then with water. The separated organic layer was dried over sodium sulfate, filtered, and concentrated to ca. 5 mL volume. Crystals separated. Added ca. 5 mL of petroleum ether and filtered; wt 0.165 g (92%); mp >290° C.
