Enantioselective radical conjugate additions driven by a photoactive intramolecular iminium-ion-based EDA complex

The photochemical activity of electron donor–acceptor (EDA) complexes provides a way to generate radicals under mild conditions. This strategy has found application in chemical synthesis and recently in enantioselective catalysis. Reported methods classically relied on the formation of intermolecula...

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Bibliographic Details
Published in:Nature communications 2018-08, Vol.9 (1), p.3274-10, Article 3274
Main Authors: Cao, Zhong-Yan, Ghosh, Tamal, Melchiorre, Paolo
Format: Article
Language:English
Subjects:
140/131
639/638/403
639/638/439
639/638/77
Absorption spectra
Carbazole
Carbazoles
Carbon
Catalysis
Charge transfer
Chemical synthesis
Conjugates
Coordination compounds
Electrons
Enantiomers
Humanities and Social Sciences
Irradiation
Laboratories
Light
Light irradiation
multidisciplinary
Optical properties
Organic chemistry
Photochemicals
Radiation
Reagents
Science
Science (multidisciplinary)
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Summary:The photochemical activity of electron donor–acceptor (EDA) complexes provides a way to generate radicals under mild conditions. This strategy has found application in chemical synthesis and recently in enantioselective catalysis. Reported methods classically relied on the formation of intermolecular EDA complexes, generated upon aggregation of two suitable reagents. Herein, we further expand the synthetic utility of this strategy demonstrating that an intramolecular EDA complex can trigger a photochemical catalytic enantioselective radical process. This approach enables radical conjugate additions to β-substituted cyclic enones to form quaternary carbon stereocenters with high stereocontrol using visible light irradiation. Crucial for success is the use of an amine catalyst, adorned with a carbazole moiety, which generates, upon condensation with enones, chiral iminium ions that show a broad absorption band in the visible region. This optical property originates from an intramolecular charge transfer π–π interaction between the electron-rich carbazole nucleus and the electron-deficient iminium double bond. In enantioselective catalysis, electron donor–acceptor (EDA) complexes are usually photochemically activated in an intermolecular fashion. Here, the authors report the stereoselective conjugate addition to β-substituted cyclic enones proceeding without external photoredox catalysts via an intramolecular EDA complex.
ISSN:2041-1723
2041-1723
DOI:10.1038/s41467-018-05375-2