N1C=CC(C(O)=O)=C1.[CH3:9][C:10]1[C:14]([C:15]([CH3:18])([CH3:17])[CH3:16])=[C:13]([CH3:19])[NH:12][C:11]=1C(OCC)=O.[OH-].[K+].C(O)(=O)C>C(O)C>[CH3:19][C:13]1[NH:12][CH:11]=[C:10]([CH3:9])[C:14]=1[C:15]([CH3:17])([CH3:16])[CH3:18]A procedure reported for the decarboxylation of derivatives of pyrrole-3-carboxylic acid was adapted from Clue, J. Org. Chem. 19:266, 1954. A solution of ethyl 3,5-dimethyl-4-tert-butylpyrrole-2-carboxylate 4g (3.0 g, 0.01 mol) and potassium hydroxide (6.0 g, 0.11 mol) in ethanol (50 ml) was heated at 80° C. for 4 h, combined with ice water (200 ml), and made slightlyacidic by the addition of acetic acid to bring about the precipitation of crude 3,5-dimethyl-4-tert-butylpyrrole-2-carboxylic acid 4 (W=CH3, X=C(CH3)3, R=CO2H). The crude acid was combined with ethanolamine (5 g), heated at 180° C. for 1 h, and diluted with ice water (100 ml) to bring about the precipitation of2,4-dimethyl-3-tert-butylpyrrole 5g as a colorless solid, 1.6 g (79%), mp 70°-71° C. (lit. 69°-71° C.) after drying in avacuum for 24 h; 1H NMR (CDCl3): δ 7.60 (br, 1H), 6.30 (s,1H), 2.25 (s, 3H), 2.15 (s, 3H), 1.28 (s, 9H). By the phosphoric acid method the pyrrole ester 4g was converted to 2,4-dimethylpyrrole 5a.
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