Unexpected Decarbonylation of Acylethynylpyrroles under the Action of Cyanomethyl Carbanion: A Robust Access to Ethynylpyrroles

Denis N Tomilin; Lyubov N Sobenina; Alexandra M Belogolova; Alexander B Trofimov; Igor A Ushakov; Boris A Trofimov

doi:10.3390/molecules28031389

Unexpected Decarbonylation of Acylethynylpyrroles under the Action of Cyanomethyl Carbanion: A Robust Access to Ethynylpyrroles

Molecules. 2023 Feb 1;28(3):1389. doi: 10.3390/molecules28031389.

Authors

Denis N Tomilin¹, Lyubov N Sobenina¹, Alexandra M Belogolova^{1

2}, Alexander B Trofimov^{1

3}, Igor A Ushakov¹, Boris A Trofimov¹

Affiliations

¹ A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Science, 664033 Irkutsk, Russia.
² Faculty of Physics, Irkutsk State University, 664003 Irkutsk, Russia.
³ Laboratory of Quantum Chemical Modeling of Molecular Systems, Irkutsk State University, 664003 Irkutsk, Russia.

Abstract

It has been found that the addition of CH₂CN^- anion to the carbonyl group of acylethynylpyrroles, generated from acetonitrile and t-BuOK, results in the formation of acetylenic alcohols, which undergo unexpectedly easy (room temperature) decomposition to ethynylpyrroles and cyanomethylphenylketones (retro-Favorsky reaction). This finding allows a robust synthesis of ethynylpyrroles in up to 95% yields to be developed. Since acylethynylpyrroles became available, the strategy thus found makes ethynylpyrroles more accessible than earlier. The quantum-chemical calculations (B2PLYP/6-311G**//B3LYP/6-311G**+C-PCM/acetonitrile) confirm the thermodynamic preference of the decomposition of the intermediate acetylenic alcohols to free ethynylpyrroles rather than their potassium derivatives.

Keywords: acylethynylpyrroles; alkynones; deacylation; retro-Favorsky reaction; terminal alkynes.

Grants and funding

This research was funded by the Ministry of Education and Science of Russian Federation (State Registration No. 121021000199-6).