Visible‐Light‐Promoted Stereoselective Alkylation by Combining Heterogeneous Photocatalysis with Organocatalysis

Cherevatskaya, Maria; Neumann, Matthias; Füldner, Stefan; Harlander, Christoph; Kümmel, Susanne; Dankesreiter, Stephan; Pfitzner, Arno; Zeitler, Kirsten; König, Burkhard

doi:10.1002/anie.201108721

Cited by 259 publications

(117 citation statements)

References 85 publications

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“…In such dual-catalyst reactions, visible-light redox sensitizers are combined with asymmetric co-catalysts, such as chiral secondary amines [9][10][11][12][13] , chiral N-heterocyclic carbenes 14 , chiral Brønsted acids 15 , chiral Lewis acids 16 , or chiral thiourea 17 . With respect to single catalysts, ultraviolet light in combination with hydrogen bonding or Lewis acid interaction has been used previously in pioneering work to trigger enantioselective catalysis [18][19][20] , and an enantioselective cycloaddition induced by visible light-although not including photoinduced electron transfer-has been reported 21 ; also, an interesting but special case of photoactivated enamine catalysis was disclosed recently in which a transient electron donoracceptor complex is capable of absorbing visible light and triggering a charge transfer 22 .…”

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confidence: 99%

Asymmetric photoredox transition-metal catalysis activated by visible light

Huo

Shen

Wang

et al. 2014

Nature

560

265

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Asymmetric catalysis is seen as one of the most economical strategies to satisfy the growing demand for enantiomerically pure small molecules in the fine chemical and pharmaceutical industries. And visible light has been recognized as an environmentally friendly and sustainable form of energy for triggering chemical transformations and catalytic chemical processes. For these reasons, visible-light-driven catalytic asymmetric chemistry is a subject of enormous current interest. Photoredox catalysis provides the opportunity to generate highly reactive radical ion intermediates with often unusual or unconventional reactivities under surprisingly mild reaction conditions. In such systems, photoactivated sensitizers initiate a single electron transfer from (or to) a closed-shell organic molecule to produce radical cations or radical anions whose reactivities are then exploited for interesting or unusual chemical transformations. However, the high reactivity of photoexcited substrates, intermediate radical ions or radicals, and the low activation barriers for follow-up reactions provide significant hurdles for the development of efficient catalytic photochemical processes that work under stereochemical control and provide chiral molecules in an asymmetric fashion. Here we report a highly efficient asymmetric catalyst that uses visible light for the necessary molecular activation, thereby combining asymmetric catalysis and photocatalysis. We show that a chiral iridium complex can serve as a sensitizer for photoredox catalysis and at the same time provide very effective asymmetric induction for the enantioselective alkylation of 2-acyl imidazoles. This new asymmetric photoredox catalyst, in which the metal centre simultaneously serves as the exclusive source of chirality, the catalytically active Lewis acid centre, and the photoredox centre, offers new opportunities for the 'green' synthesis of non-racemic chiral molecules.

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confidence: 99%

Asymmetric photoredox transition-metal catalysis activated by visible light

Huo

Shen

Wang

et al. 2014

Nature

560

265

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“…[89] Mechanistisch (68) in enantioselektiven a-Alkylierungen über-nehmen kçnnen. [92] In neueren Arbeiten haben Melchiorre und Mitarbeiter gezeigt, dass in vielen Fällen für die a-Alkylierung von Aldehyden [77] und Ketonen [93] kein zweiter Katalysator bençtigt wird. Vielmehr genügt eine direkte Anregung mit sichtbarem Licht, um derartige Alkylierungen durchzuführen.…”

Section: Amineunclassified

Enantioselektive Katalyse photochemischer Reaktionen

et al. 2015

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Die Natur des angeregten Zustands macht die Entwicklung chiraler Katalysatoren für enantioselektive photochemische Reaktionen zu einer enormen Herausforderung. Die Absorption eines 400‐nm‐Photons entspricht einer Energieaufnahme von etwa 300 kJ mol−1. Es bedarf innovativer Konzepte, um in einem derart großen Abstand vom Grundzustand Reaktionspfade zu eröffnen, die gezielt zu einem Enantiomer einer chiralen Verbindung führen. Hier werden die beiden wesentlichen Vorgehensweisen für homogen katalysierte, enantioselektive Prozesse diskutiert. Im ersten Teil werden chirale Photokatalysatoren besprochen, die in den photochemischen Schlüsselschritt eingreifen und in diesem Schritt eine asymmetrische Induktion bewirken. Im zweiten Teil werden Reaktionen vorgestellt, in denen die photochemische Anregung durch einen achiralen Katalysator erfolgt und die asymmetrische Induktion durch einen zweiten chiralen Katalysator gewährleistet wird (duale Katalyse).

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“…For example, König and co-workers have reported that heterogeneous photocatalysis has been combined with organocatalysis to promote stereoselective alkylation with visiblelight (Scheme 11). 16 This work was extended to the asymmetric synthesis of α-functionalised aldehydes using the MacMillan oxazolidinone catalyst 10, PbBiO 2 Br and light (Scheme 12). 17 The dual catalysis process employs an organo/metal cooperative system under mild conditions using molecular oxygen as a terminal oxidant, with moderate to good yields (47−82%) and excellent enantiomeric ratios (up to 99.5:0.5 er) when employing copper(II) triflate and quinine 11 as catalysts.…”

Section: Bifunctional Organocatalysismentioning

confidence: 99%