The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Synthesis of pyrrolecarboxaldehydes》. Authors are Ghigi, Elisa; Drusiani, Annamaria.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).Computed Properties of C9H13NO2. Through the article, more information about this compound (cas:2199-44-2) is conveyed.
HCO-NMe2 (I) (23.89 g.) and 58.25 g. POCl3 warmed after 10 min. to 60°, treated dropwise in 1.5 hrs. with 18 g. 2,4-dimethylpyrrole in an equal volume of I, the mixture stirred 1 hr. at 60°, poured into 333 g. ice and 245 g. fused NaOAc, the mixture boiled, cooled, extracted with Et2O, the extract evaporated free from Et2O and made alk. with powd. Na2CO3, filtered, and the residual product (II) dried. Further extraction of the filtrate with Et2O gave another 0.69 g. II. II boiled in petr. ether, the solution purified with C, filtered and cooled gave 0.6 g. (crude) 2,4-dimethyl-3,5-pyrroledicarboxaldehyde, m. 165-6° (from H2O), and 9.6 g. (crude) 2,4-dimethyl-5-pyrrolecarboxaldehyde, m. 89-90° (from H2O). Similarly, I and POCl3 at 60°, treated dropwise with stirring with 2,4-dimethyl-8-ethylpyrrole gave 2,4-dimethyl-3-ethyl-5-pyrrolecarboxaldehyde, m. 105-6°. In the same way, 1.79 g. I and 4.37 g. POCl3 treated with 1.35 g. 2,3,4-trimethylpyrrole gave 0.3 g. 2,3,4-trimethyl-5-pyrrolecarboxaldehyde, m. 147°; 2.6 g. I and 6.32 g. POCl3 with 3 g. Et 2,4-dimethyl-3-pyrrolecarboxylate in I yielded Et 2,4-dimethyl-5-formyl-3-pyrrolecarboxylate, m. 165°; 8.6 g. I and 21 g. POCl3 with 10 g. Et 2,4-dimethyl-5-pyrrolecarboxylate and 10 g. I produced 11.2 g. Et 2,4-dimethyl-3-formyl-5-pyrrolecarboxylate, m. 145°. Heating 20 g. 2,4-dimethyl-5-carbethoxy-3-pyrrolecarboxylate at 200° with 200 g. quinoline and 2 g. finely divided pure Cu to cessation of CO2 evolution, cooling, filtering, acidifying the filtrate with 50% HCl, filtering, washing the precipitate with H2O, and drying gave 11.2 g. Et 2,4-dimethyl-5-pyrrolecarboxylic acid, m. 122°.
In addition to the literature in the link below, there is a lot of literature about this compound(Ethyl 3,5-Dimethyl-2-pyrrolecarboxylate)Computed Properties of C9H13NO2, illustrating the importance and wide applicability of this compound(2199-44-2).
Reference:
Thiazolidine – Wikipedia,
Thiazolidine – ScienceDirect.com