[CH3:1][N:2]1[CH:6]=[C:5]([N+:7]([O-:9])=[O:8])[CH:4]=[C:3]1[CH:10]=O.C(O)(=O)[CH2:13][C:14]([OH:16])=[O:15].OS(O)(=O)=O>N1CCCCC1.N1C=CC=CC=1>[CH3:1][N:2]1[CH:6]=[C:5]([N+:7]([O-:9])=[O:8])[CH:4]=[C:3]1/[CH:10]=[CH:13]/[C:14]([OH:16])=[O:15]Alternatively, a mixture of 1-methyl-4-nitro-2-pyrrolecarboxaldehyde (0.20 g, 1.30 mmol), malonic acid (0.68 g, 6.5 mmol), piperidine (2 drops), and pyridine (2 mL) was stirred at room temperature at for 20 h and at 100° C. for 4 h, then 30% aqueous H2SO4 (10 mL) was added. The precipitate that formed was removed by filtration and washed with water to give (E)-1-methyl-4-nitro-2-pyrroleacrylic acid as fine yellow needles (0.23 g, 92%). 1H NMR [(CD3)2SO] δ 12.35 (br s, 1 H, CO2H), 8.13 (d, J=1.9 Hz, 1 H, H-5), 7.44 (d, J=15.9 Hz, 1 H, H-β), 7.41 (d, J=1.9 Hz, 1 H, H-3), 6.46 (d, J=15.9 Hz, 1 H, H-α), 3.79 (s, 3 H, NCH3); 13C NMR δ 167.4 (CO2H), 135.3, 129.9 (C-2,4), 130.6, 127.0, 118.6, 105.8 (C-3,5,α,β), 34.8 (NCH3).
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