[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 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 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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