The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《A novel route to certain 2-pyrrolecarboxylic esters and nitriles》. Authors are Kleinspehn, Geo. G..The article about the compound:Ethyl 3,5-Dimethyl-2-pyrrolecarboxylatecas:2199-44-2,SMILESS:O=C(C1=C(C)C=C(C)N1)OCC).Name: Ethyl 3,5-Dimethyl-2-pyrrolecarboxylate. Through the article, more information about this compound (cas:2199-44-2) is conveyed.
HON:C(CO2Et)2 (I) underwent reduction and condensation with certain β-diketones and a β-oxo aldehyde to give 2-pyrrolecarboxylic esters. Similarly, HON:C(CN)CO2Et (II) and certain β-diketones afforded 2-pyrrolecarbonitriles. The method has been applied to the synthesis of 5 previously known pyrroles. This synthetic approach constitutes the most direct route to 4 of these 5 pyrroles. A sixth and previously unreported pyrrole, 3,5-dimethyl-2-pyrrolecarbonitrile (III), also has been prepared by this method. Ac2CH2 (5.00 g.) in 26 cc. glacial AcOH heated with vigorous stirring at 80° with 13 g. NaOAc and 11 g. Zn dust, the mixture then treated with 9.47 g. I in 12 cc. AcOH and 5 cc. H2O dropwise at 95-105° during 30-40 min., heated 20 min. at 100-5°, poured with stirring into 170 cc. ice water, and refrigerated, the precipitate washed with H2O, pressed dry, dissolved in 50 cc. boiling EtOH, and filtered hot, the filtrate concentrated to 30 cc., poured into 85 cc. ice water, and refrigerated, and the crystalline deposit dried in vacuo (5.03 g.), and recrystallized twice from 95% EtOH yielded 2-carbethoxy-3,5-dimethylpyrrole (IV), m. 124-4.5°. I and Ac2CHEt (50 millimole each), b23-3.5 79-83.5°, gave by the same procedure 6.36 g. 4-Et derivative of IV, m. 90-1° (from 95% EtOH). I and Ac2CH(CH2)2CO2H (50 millimoles) treated in the same manner, the reaction mixture treated with 5 cc. concentrated HCl, and the crude product (7.08 g.) recrystallized from boiling C6H6 gave 5-carbethoxy-2,4-dimethyl-3-pyrrolepropionic acid, m. 154-6°. NaOAc (7.9 g.) added with stirring to 29 cc. glacial AcOH at 85°, the mixture treated with 7.00 g. AcCHMeCHO, 9.48 g. I, and 12 cc. glacial AcOH in 5 cc. H2O, followed by 11 g. Zn dust at 95-105°, stirred 20 min., poured into 170 cc. ice water, and refrigerated, and the deposit dissolved in 10 cc. boiling EtOH and filtered, the filtrate poured into 20 cc. ice water, and the precipitate (2.49 g.) recrystallized from 95% EtOH and then twice from isoöctane gave 2-carbethoxy-3,4-dimethylpyrrole (V), m. 75-6.5°. V heated briefly in EtOH with excess 40% aqueous CH2O and a few drops concentrated HCl yielded 5,5′-methylenebis(2-carbethoxy-3,4-dimethylpyrrole), m. 202-3°. II and Ac2CH2 (50 millimoles each) treated by the usual procedure, the crude product containing the Zn dust dissolved in 25 cc. boiling 95% EtOH, and the filtrate poured into 75 cc. ice water yielded 2.48 g. IV, m. 24-5° (recrystallized from EtOH and sublimed). Glacial AcOH (26 cc.) and 5.00 g. Ac2CH2 heated to 80°, the mixture treated consecutively with 13 g. NaOAc, 7.11 g. II, and 12 cc. AcOH in 5 cc. H2O, heated to 95°, treated during 20-5 min. with 11 g. Zn dust at 95-105°, stirred 20 min., and poured into ice water, the precipitate refrigerated, filtered off, dissolved in 15 cc. boiling EtOH, and filtered, the filtrate stirred into 30 cc. ice water and refrigerated, and the crude precipitate (2.10 g.) recrystallized twice from isoöctane yielded III, m. 75-6.5°. II and Ac2CHEt gave similarly 45% crude 4-Et derivative of III, m. 135-6°.
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Reference:
Thiazolidine – Wikipedia,
Thiazolidine – ScienceDirect.com