[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 (1 g, 5.43 mmol) in DCM (60 mL) is added MCPBA (2.81 g, 16.29 mmol) portion wise at room temperature. The resulting solution is stirred at room temperature overnight. A solution of Na2S2O3 (1.6 g) in water (60 mL) is added. The mixture is stirred at room temperature for 20 min. The layer is separated, and the water layer is extracted with DCM (2×20 mL). The combined DCM layer is washed with saturated NaHCO3 (3×20 mL), dried (Na2SO4), filtered and concentrated in vacuo to afford 2-methanesulfonyl-pyrimidine-5-carboxylic acid methyl ester as a solid (1.05 g, 90%). 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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