[Cl:1][C:2]1[S:3][C:4]([C:9]([O:11][CH2:12][CH3:13])=[O:10])=[C:5]([CH2:7][OH:8])[N:6]=1.C([OH:17])(C)C>CC(C)=O.S(=O)(=O)(O)O.O.[O-2].[O-2].[O-2].[Cr+6]>[Cl:1][C:2]1[S:3][C:4]([C:9]([O:11][CH2:12][CH3:13])=[O:10])=[C:5]([C:7]([OH:17])=[O:8])[N:6]=1To a solution of ethyl 2-chloro-4-(hydroxymethyl)-1,3-thiazole-5-carboxylate (Intermediate 8, 2.5 g, 11 mmol) in acetone at 0° C. was slowly added a solution of chromium trioxide (2.26 g, 22 mmol) in 20% conc. Sulfuric acid in water (20 mL). After stirring at room temperature for 2 hrs, isopropanol (1 mL) was added to quench unreacted chromium trioxide. The reaction was diluted with water and the acetone was removed. Partitioning with methylene chloride (×3), drying with MgSO4 and concentrating yielded a white solid (2.3 g, 90%). MS (ES): 236 (M+H+) for C7H6ClNO4S; NMR: 1.26 (t, 3H), 4.31 (q, 2H), 13.99-14.15 (m, 1H).
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