Citric Acid → 3-bromo-1H-pyrrole-2-carboxylic acid
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[Br:1][C:2]1[CH:6]=[CH:5][NH:4][C:3]=1[CH:7]=[O:8].CC(=CC)C.C1C[O:17]CC1.Cl([O-])=O.[Na+].C(O)(=O)CC(CC(O)=O)(C(O)=O)O>C(O)(C)(C)C.O>[Br:1][C:2]1[CH:6]=[CH:5][NH:4][C:3]=1[C:7]([OH:17])=[O:8][Br:1][C:2]1[CH:6]=[CH:5][NH:4][C:3]=1[CH:7]=[O:8].CC(=CC)C.C1C[O:17]CC1.Cl([O-])=O.[Na+].C(O)(=O)CC(CC(O)=O)(C(O)=O)O>C(O)(C)(C)C.O>[Br:1][C:2]1[CH:6]=[CH:5][NH:4][C:3]=1[C:7]([OH:17])=[O:8]
To a solution of 3-bromo-1H-pyrrole-2-carbaldehyde (0.44 g, 2.53 mmol) in tert-butanol (5.0 ml) was added 2-methyl-2-butene/2M in THF (5.09 ml, 48.0 mmol). To the reaction mixture was added sodium phosphate mono-H2O (2.461 g, 17.70 mmol) and sodium chlorite (2.058 g, 22.76 mmol) dissolved in water (5.00 ml) at RT over a period of 15 min. The solution was stirred overnight. The reaction mixture was acidified to pH˜4 with 10% aqueous citric acid and extracted with EtOAc (5×30 mL). The organic layers were combined, dried over sodium sulfate filtered and evaporated. The crude material was triturated with minimal amount of EtOAc to afford 3-bromo-1H-pyrrole-2-carboxylic acid (0.35 g, 73% yield) as a tan solid. The filtrate solution was evaporated to afford an impure mixture of the product as an oil. 1H NMR (400 MHz, DMSO-d6): δ ppm 12.55 (br. s., 1H) 12.00 (br. s., 1H) 6.96 (t, 1H) 6.26 (t, 1H). MS: m/z 188.0 (M−1).
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