Abstract
It was shown by 1H NMR spectroscopy that 2-(5-R1-2-furyl)-3-R2-1-R1-pyrroles (R1= H, Me; R2=H, Me; R3=H, Et, CH=CH2) are protonated by acids (HSO3F, HCO2CF3, HCl, HBr) either at the C(5) atom of the pyrrole ring or at the C(5′) atom of the furan ring, depending on the conditions. The energies of formation (δH), the charges, and the partial electron densities of the boundary orbitals of 2-(2-furyl)pyrrole (I) and its protonated forms (IA and IB) were calculated by the MNDO method. The calculated δH values for the IA and IB forms are in agreement with their experimental ratio. According to the calculated reactivity indexes, the protonation of pyrrole is subject to orbital control and may include the prior formation of less stable protonated forms.
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Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1343–1355, October, 1989.
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Sigalov, M.V., Shmidt, E.Y., Trofimov, A.B. et al. Protonated forms of 2-(2-furyl)pyrroles and their interconversions. Chem Heterocycl Compd 25, 1122–1133 (1989). https://doi.org/10.1007/BF00470690
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DOI: https://doi.org/10.1007/BF00470690