CC(C)=[O:3].OS(O)(=O)=O.O=[Cr](=O)=O.S(=O)(=O)(O)O.[CH3:19][O:20][C:21]([C:23]1[N:24]([S:30]([CH3:33])(=[O:32])=[O:31])[CH:25]=[C:26]([CH:28]=[O:29])[CH:27]=1)=[O:22]>O.CC(C)=O>[CH3:19][O:20][C:21]([C:23]1[N:24]([S:30]([CH3:33])(=[O:32])=[O:31])[CH:25]=[C:26]([C:28]([OH:3])=[O:29])[CH:27]=1)=[O:22]The Jones reagent was made up in 1.00-mol batches by dissolving 100 g of CrO3 in a minimum of distilled water. Sulfuric acid (87 mL) was added and more water (200 mL total) was then added to effect solution of precipitated CrO3. The final volume was 350 mL (2.86 M with respect to CrO3). To a solution of 4-formyl-1-methanesulfonyl-1H-pyrrole-2-carboxylic acid methyl ester (700 mg, 3.03 mmol) in acetone (5 mL) was added the Jones reagent at 10° C. dropwise until a persistent orange color was observed. The reaction mixture was stirred for additional 20 minutes, and then the orange color was removed by the addition of isopropyl alcohol. After dilution with water (20 mL) the solution was extracted with CHCl3 (3×30 mL). The combined organic layers were washed once by water and then extracted to aqueous NaHCO3 solution (60 mL). The NaHCO3 solution was acidified by concentrated HCl to pH 2 and the resulting white precipitate was collected by filtration and washed with cold water. The crude product was dried on the oil pump for the next step without further purification (600 mg, 80%). 1H NMR (500 MHz, DMSO-d6) δ12.87 (s, 1H), 7.91 (s, 1H), 7.30 (s, 1H), 3.93 (s, 3H), 3.84 (s, 3H) ppm. MS (ES+): m/e=248.1 (M+H); LC/Method A/2.38 min.
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