Dimethyl Sulfoxide → 3-(2,6-dichlorophenyl)-7-methanesulfonyl-1-methyl-3,4-dihydropyrimido[4,5-d]pyrimidin-2(1H)-one

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A solution of 3-(2,6-dichlorophenyl)-7-methylthio-1-methyl-3,4-dihydropyrimido[4,5-d]pyrimidin-2(1H)-one (1.1) (5 g, 14.1 mmol) in 200 mL of dichloromethane was cooled in ice and treated with 3-chloroperbenzoic acid (10 g, 28.9 mmol). The mixture was stirred at room temperature for 17 hours, then treated with 2 mL of dimethyl sulfoxide and left to stand for 10 minutes. Saturated aqueous sodium bicarbonate solution (100 mL) was then added and the phases were separated. The organic phase was dried over magnesium sulfate and filtered. Concentration of the filtrate under reduced pressure gave 5 g (92%) of 3-(2,6-dichlorophenyl)-7-methanesulfonyl-1-methyl-3,4-dihydropyrimido[4,5-d]pyrimidin-2(1H)-one (sulfone 1.2) as a white solid.

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