[CH3:1][O:2][C:3]([C:5]1[CH:6]=[N:7][C:8](SC)=[N:9][CH:10]=1)=[O:4].[CH:13]1C=C(Cl)C=C(C(OO)=O)C=1.[O-:24][S:25]([O-:28])(=S)=O.[Na+].[Na+]>C(Cl)Cl.O>[CH3:1][O:2][C:3]([C:5]1[CH:10]=[N:9][C:8]([S:25]([CH3:13])(=[O:28])=[O:24])=[N:7][CH:6]=1)=[O:4]To a solution of 2-methylsulfanyl-pyrimidine-5-carboxylic acid methyl ester (1 g, 5.43 mmol) in DCM (60 mL) is added MCPBA (2.81 g, 16.29 mmol) portion wise at rt. The resulting solution is stirred at rt overnight. A solution of Na2S2O3 (1.6 g) in water (60 mL) is added. The mixture is stirred at rt for 20 min. The organic layer and aqueous layer are separated, and the aqueous layer is extracted with DCM (2×20 mL). The combined organic layer is washed with saturated aqueous NaHCO3 (3×20 mL), dried (Na2SO4), filtered and concentrated in vacuo to afford 2-methanesulfonyl-pyrimidine-5-carboxylic acid methyl ester (1.05 g, 90%) as a solid. MS: 217 (M+H); 1H NMR (300 MHz, CDCl3): δ 3.41 (s, 3H), 4.06 (s, 3H), 9.44 (s, 2H).
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