Bartling, Hanna and Eisenhofer, Anna and Koenig, Burkhard and Gschwind, Ruth M. (2016) The Photocatalyzed Aza-Henry Reaction of N-Aryltetrahydroisoquinolines: Comprehensive Mechanism, H-center dot-versus H+-Abstraction, and Background Reactions. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 138 (36). pp. 11860-11871. ISSN 0002-7863,
Full text not available from this repository. (Request a copy)Abstract
The cross-dehydrogenative coupling (CDC) reaction of N-aryltetrahydroisoquinolines (THIQ) is one of the most exploited photocatalytic transformation and a test reaction for an exceptional Variety of catalysts. However, its mechanism remained unclear concerning involved intermediates, reactive pathways of the amine radical cation and the influence of oxygen and the light source. Therefore, nuclear magnetic resonance (NMR), electron spin resonance (ESR) and synthetic method's were combined to provide a comprehensive picture of the reaction mechanism using Ru(bpy)(3)Cl-2 as a photocatalyst under aerobic and anaerobic conditions. The reaction profiles and involved intermediates were monitored and analyzed by NMR spectroscopy. Several intermediates contributing to product formation were identified, the iminium ion, the hydroperoxide and dimes of THIQ and a new ring opened intermediate; cleaved at the benzylic C-N bond. Mechanistic evidence is given that under anaerobic conditions preferentially the alpha-amino radical is formed by deprotonation, in contrast to the formation of iminium ions via H-center dot-abstraction in the presence of oxygen. Further, the light-induced background reaction in the absence of the catalyst was studied in detail, revealing that the product formation rate is correlated to the intensity and wavelength of the light source and that oxygen is essential for an efficient conversion. The reaction rate and efficiency is comparable to previously repotted photocatalytic systems, performed under aerobic conditions in combination with intense blue light sources. Thus, the multitude of reaction parameters investigated reveals the preference for hydrogen atom or proton abstraction in photoreactions and allows to assess the influence of experimental conditions on the mechanistic pathways.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | LIGHT PHOTOREDOX CATALYSIS; DEHYDROGENATIVE-COUPLING REACTIONS; PHOTOINDUCED ELECTRON-TRANSFER; HYDROGEN-ATOM TRANSFER; TRANSITION-METAL-COMPLEXES; ALPHA-AMINOALKYL RADICALS; PROTON-TRANSFER REACTIONS; ACI-NITRO TAUTOMERISM; CARBON BOND FORMATION; OXIDATIVE C-C; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Lehrstuhl Prof. Dr. Burkhard König Chemistry and Pharmacy > Institut für Organische Chemie > Arbeitskreis Prof. Dr. Ruth Gschwind |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 03 Apr 2019 11:59 |
| Last Modified: | 03 Apr 2019 11:59 |
| URI: | https://pred.uni-regensburg.de/id/eprint/3290 |
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