Enantioselective Photoredox Catalysis Enabled by Proton-Coupled Electron Transfer: Development of an Asymmetric Aza-Pinacol Cyclization

Rono, Lydia J.; Yayla, Hatice G.; Wang, David Y.; Armstrong, Michael F.; Knowles, Robert R.

doi:10.1021/ja4100595

Cited by 421 publications

(257 citation statements)

References 51 publications

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“…However, following PCET, the H-bond complex may persist to provide a discrete association between the nascent radical and the conjugate base of the proton donor, providing a basis for asymmetric induction when chiral phosphoric acids are employed. 7 …”

Section: Introductionmentioning

confidence: 99%

Enantioselective Synthesis of Pyrroloindolines via Noncovalent Stabilization of Indole Radical Cations and Applications to the Synthesis of Alkaloid Natural Products

et al. 2018

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While interest in the synthetic chemistry of radical cations continues to grow, controlling enantioselectivity in the reactions of these intermediates remains a challenge. Based on recent insights into the oxidation of tryptophan in enzymatic systems, we report a photocatalytic method for the generation of indole radical cations as hydrogen-bonded adducts with chiral phosphate anions. These non-covalent open-shell complexes can be intercepted by the stable nitroxyl radical TEMPO• to form alkoxyamine-substituted pyrroloindolines with high levels of enantioselectivity. Further elaboration of these optically-enriched adducts can be achieved via a catalytic single-electron oxidation/mesolytic cleavage sequence to furnish transient carbocation intermediates that may be intercepted by a wide range of nucleophiles. Taken together, this two-step sequence provides a simple catalytic method to access a wide range of substituted pyrroloindolines in enantioenriched form via a standard experimental protocol from a common synthetic intermediate. The design, development, mechanistic study, and scope of this process are presented, as are applications of this method to the synthesis of several dimeric pyrroloindoline natural products.

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Section: Introductionmentioning

confidence: 99%

Enantioselective Synthesis of Pyrroloindolines via Noncovalent Stabilization of Indole Radical Cations and Applications to the Synthesis of Alkaloid Natural Products

et al. 2018

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“…2 A number of novel dual catalytic systems have recently been developed to address this long-standing problem. The combination of transition metal photoredox catalysts with chiral amine, 3 carbene, 4 and Brønsted acid organocatalysts 5 has enabled a number of highly enantioselective photoinduced reactions. We recently reported the first method combining photoredox and chiral Lewis acid catalysis in the context of an asymmetric [2+2] photocycloaddition.…”

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confidence: 99%

Enantioselective Conjugate Additions of α-Amino Radicals via Cooperative Photoredox and Lewis Acid Catalysis

et al. 2015

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We report the highly enantioselective addition of photogenerated α-amino radicals to Michael acceptors. This method features a dual-catalyst protocol that combines transition metal photoredox catalysis with chiral Lewis acid catalysis. The combination of these two powerful modes of catalysis provides an effective, general strategy to generate and control the reactivity of photogenerated reactive intermediates.

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“…[103] Dabei wurden mit hoher Diastereo-und Enantioselektivität die Produkte 83 gebildet. Als Mechanismus wird vorgeschlagen, dass der aus [Ir(ppy) 2 (dtb-bpy)]PF 6 (69) entstehende, reduzierte Ir II -Komplex einen protonengekoppelten Elektronentransfer auf die Ketogruppe des Substrats induziert.…”

Section: Anionen Als Gegenionenunclassified

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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Enantioselective Photoredox Catalysis Enabled by Proton-Coupled Electron Transfer: Development of an Asymmetric Aza-Pinacol Cyclization

Cited by 421 publications

References 51 publications

Enantioselective Synthesis of Pyrroloindolines via Noncovalent Stabilization of Indole Radical Cations and Applications to the Synthesis of Alkaloid Natural Products

Enantioselective Synthesis of Pyrroloindolines via Noncovalent Stabilization of Indole Radical Cations and Applications to the Synthesis of Alkaloid Natural Products

Enantioselective Conjugate Additions of α-Amino Radicals via Cooperative Photoredox and Lewis Acid Catalysis

Enantioselektive Katalyse photochemischer Reaktionen

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