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Pann J, Erharter K, Langerreiter D, Partl G, Müller T, Schottenberger H, Hummel M, Hofer TS, Kreutz C, Fliri L. Mechanistic Insights into the Formation of 1-Alkylidene/Arylidene-1,2,4-triazolinium Salts: A Combined NMR/Density Functional Theory Approach. J Org Chem 2022; 87:1019-1031. [PMID: 34978817 PMCID: PMC8790756 DOI: 10.1021/acs.joc.1c02327] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Indexed: 11/29/2022]
Abstract
In a recent report on the synthetic approach to the novel substance class of 1-alkylidene/arylidene-1,2,4-triazolinium salts, a reaction mechanism suggesting a regioselective outcome was proposed. This hypothesis was tested via a combined NMR and density functional theory (DFT) approach. To this end, three experiments with 13C-labeled carbonyl reactants were monitored in situ by solution-state NMR. In one experiment, an intermediate as described in the former mechanistic proposal was observed. However, incorporation of 13C isotope labels into multiple sites of the heterocycle could not be reconciled with the "regioselective mechanism". It was found that an unproductive reaction pathway can lead to 13C scrambling, along with metathetical carbonyl exchange. According to DFT calculations, the concurring reaction pathways are connected via a thermodynamically controlled cyclic 1,3-oxazetidine intermediate. The obtained insights were applied in a synthetic study including aliphatic ketones and para-substituted benzaldehydes. The mechanistic peculiarities set the potential synthetic scope of the novel reaction type.
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Affiliation(s)
- Johann Pann
- Institute
of General, Inorganic Chemistry and Theoretical Chemistry, Faculty
of Chemistry and Pharmacy, University of
Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Kevin Erharter
- Institute
of Organic Chemistry and Center for Molecular Bioscience Innsbruck
(CMBI), Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Daniel Langerreiter
- Department
of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, 0076 Aalto, Finland
| | - Gabriel Partl
- Institute
of General, Inorganic Chemistry and Theoretical Chemistry, Faculty
of Chemistry and Pharmacy, University of
Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Thomas Müller
- Institute
of Organic Chemistry and Center for Molecular Bioscience Innsbruck
(CMBI), Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Herwig Schottenberger
- Institute
of General, Inorganic Chemistry and Theoretical Chemistry, Faculty
of Chemistry and Pharmacy, University of
Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Michael Hummel
- Department
of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, 0076 Aalto, Finland
| | - Thomas S. Hofer
- Institute
of General, Inorganic Chemistry and Theoretical Chemistry, Faculty
of Chemistry and Pharmacy, University of
Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Christoph Kreutz
- Institute
of Organic Chemistry and Center for Molecular Bioscience Innsbruck
(CMBI), Faculty of Chemistry and Pharmacy, University of Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
| | - Lukas Fliri
- Institute
of General, Inorganic Chemistry and Theoretical Chemistry, Faculty
of Chemistry and Pharmacy, University of
Innsbruck, Innrain 80-82, 6020 Innsbruck, Austria
- Department
of Bioproducts and Biosystems, Aalto University, P.O. Box 16300, 0076 Aalto, Finland
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Nerdinger S, Schottenberger H, Neuner S, A. Schwartz H, Kreutz C, Müller T, Mayer P, Bonn G, Gelbrich T, J. Griesser U, Wurst K, Kahlenberg V. 2-Arylazoimidazoles Revamped by Quarternization or Dimerization; Another Gain in Functionality of an Industrial Dyestuff Family by Task-Specific Side-Chain Substituents. HETEROCYCLES 2022. [DOI: 10.3987/com-22-s(r)17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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