2,3-Dichloro-5,6-dicyano-1,4-benzoquinone → 5-phenyl-1H-pyrrole-2-carboxylic acid

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Reaction Steps

To a 1L round bottomed flask with a stirring bar and an argon inlet was added 5-phenyl-3,4-dihydro-2H-pyrrole-2-carboxylic acid ethyl ester AV-4-1 (4.84 g, 22.28 mmol), dry CH2Cl2 (220 mL) and DDQ (5.06 g, 22.28 mmol). This solution was stirred at ambient temperature 1 h. The solvent was removed in vacuo. Aqueous NaOH (10% w/v, 440 mL) was added and the mixture was heated at reflux 24 h. The cooled, black solution was poured onto crushed ice and the mixture was acidified with conc. HCl. This mixture was extracted with EtOAc (2×). The combined extracts were washed with brine, dried (MgSO4), filtered and concentrated in vacuo. The crude product was chromatographed on silica gel using 2.5% MeOH in EtOAc as eluant to give 5-phenyl-1H-pyrrole-2-carboxylic acid AV-5-1 as an off white solid. 1H NMR (CDCl3) δ 6.59 (1H, dd, j=2.7, 3.9 Hz), 7.13 (1H, dd, j=2.7, 3.9 Hz), 7.34 (1H, m), 7.41 (2H, m), 7.59 (2H, m), 9.40 (1H, br s).

Provenance & Evidence