Oxidative Catalysis Using the Stoichiometric Oxidant as a Reagent: An Efficient Strategy for Single‐Electron‐Transfer‐Induced Tandem Anion–Radical Reactions

Kafka, František; Holan, Martin; Hidasová, Denisa; Pohl, Radek; Cı́sařová, Ivana; Klepetářová, Blanka; Jahn, Ullrich

doi:10.1002/anie.201403776

Cited by 51 publications

(35 citation statements)

References 46 publications

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“…All starting ketones 6 were prepared in high yields by reacting the enolate of the corresponding ketones with 3 and 4 (Scheme ),34 with the exception of substrates 6i , 6j , (2 S *,6 R *)‐ 6l and (2 S *,6 S *)‐ 6l , which were synthesized by using the recently developed ferrocene‐catalyzed oxygenation with 1‐oxo‐2,2,6,6‐piperidinium hexafluorophosphate as the stoichiometric oxidant and reagent 37…”

Section: Resultsmentioning

confidence: 99%

Facile and Highly Diastereoselective Synthesis of syn‐ and cis‐1,2‐Diol Derivatives from Protected α‐Hydroxy Ketones

et al. 2015

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An efficient method for the synthesis of monoprotected syn‐ or cis‐1,2‐diol derivatives by reduction of easily accessible α‐(2,2,6,6‐tetramethylpiperidinyloxy) ketones is reported. The α‐(tetramethylpiperidinyloxy) group as the stereodirecting group induces in unhindered acyclic or cyclic ketones complete syn‐ or cis‐diastereoselectivity, respectively, with L‐Selectride. For more hindered derivatives, where L‐Selectride becomes unreactive, LiAlH4 proved effective, essentially showing the same high selectivity. The diastereoselectivity of the reduction can be rationalized for acyclic ketones by the Felkin–Anh model, whereas for cyclic substrates, attack from the face opposite to the tetramethylpiperidinyloxy group predictably prevails with high selectivity regardless of the substitution pattern. The liberation of free diols was achieved by reductive N–O bond cleavage of the alkoxyamine unit.

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Section: Resultsmentioning

confidence: 99%

Facile and Highly Diastereoselective Synthesis of syn‐ and cis‐1,2‐Diol Derivatives from Protected α‐Hydroxy Ketones

et al. 2015

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“…All resulting enolates 3 − (and 2 − ) undergo facile SET oxidation by ferrocenium hexafluorophosphate 4 , to generate efficiently the corresponding radicals 30 . All substrates can now also be envisaged to be oxidized by catalytic amounts of 4 , based on very recent results 21. The major path of stabilization is cyclization, which proceeds under very mild conditions.…”

Section: Discussionmentioning

confidence: 99%

Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions

Holan

Pohl

Cı́sařová

et al. 2015

Chemistry A European J

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Densely functionalized cyclopentane derivatives with up to four consecutive stereocenters are assembled by a tandem Michael addition/single-electron transfer oxidation/radical cyclization/oxygenation strategy mediated by ferrocenium hexafluorophosphate, a recyclable, less toxic single-electron transfer oxidant. Ester enolates were coupled with α-benzylidene and α-alkylidene β-dicarbonyl compounds with switchable diastereoselectivity. This pivotal steering element subsequently controls the diastereoselectivity of the radical cyclization step. The substitution pattern of the radical cyclization acceptor enables a switch of the cyclization mode from a 5-exo pattern for terminally substituted olefin units to a 6-endo mode for internally substituted acceptors. The oxidative anionic/radical strategy also allows efficient termination by oxygenation with the free radical 2,2,6,6-tetramethyl-1-piperidinoxyl, and two C-C bonds and one C-O bond are thus formed in the sequence. A stereochemical model is proposed that accounts for all of the experimental results and allows the prediction of the stereochemical outcome. Further transformations of the synthesized cyclopentanes are reported.

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“…Für die oxidative Radikalerzeugung mit stöchiometrischen Mengen TEMPO + wird in Abbildung ein elegantes Beispiel aus der Jahn‐Gruppe präsentiert . Das Ferrocenium‐Ion wird als katalytischer Redox‐Vermittler eingesetzt, um zunächst das Lithiumenolat 19 zu oxidieren, wodurch Ferrocen und das entsprechende α‐Keto‐Radikal 20 , welches anschließend ein 5‐ exo ‐Cyclisierung zu Radikal 21 eingeht, gebildet werden.…”

Section: Metall‐freie Prozesseunclassified

Der “Persistent Radical Effect” in der organischen Chemie

2019

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Radikal‐Radikal‐Kupplungen sind nahezu diffusionskontrollierte Prozesse. Daher sind selektive Kreuzkupplungen zweier unterschiedlicher Radikale schwierig zu realisieren und stellen somit synthetisch nicht wertvolle Prozesse dar. Wenn die beiden Radikale allerdings eine unterschiedliche Lebensdauer aufweisen und in gleichen Raten gebildet werden, wird die Kreuzkupplung zum dominierenden Prozess. Die hohe Kreuzselektivität basiert auf einem kinetischen Phänomen, dem “Persistent Radical Effect” (PRE). In diesem Aufsatz wird eine von Simulationen einfacher Modellsysteme gestützte Erklärung des PRE geliefert. Weiter werden die Stabilität von Radikalen in Bezug auf ihre Lebensdauer und verschiedene Beispiele für PRE‐vermittelte Radikal‐Radikal‐Kupplungen in der Synthese diskutiert. Es wird gezeigt, dass der PRE nicht auf Kupplungen persistenter mit transienten Radikalen beschränkt ist. Der PRE mit einhergehender hoher Kreuzselektivität greift bereits, wenn ein Kupplungspartner langlebiger als das andere transiente Radikal ist. Diese Tatsache erweitert signifikant das Anwendungsgebiet PRE‐vermittelter Radikalchemie. Dieser Aufsatz ist in zwei Teile aufgeteilt: 1) die Kupplung persistenter oder langlebiger organischer Radikale und 2) Radikal‐Metall‐Kreuzungsreaktionen; hierbei werden Metall‐zentrierte Radikalspezies oder allgemeiner langlebige Übergangsmetallkomplexe, welche mit Radikalen reagieren, diskutiert – ein Gebiet, das jüngst stark expandiert ist.

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Oxidative Catalysis Using the Stoichiometric Oxidant as a Reagent: An Efficient Strategy for Single‐Electron‐Transfer‐Induced Tandem Anion–Radical Reactions

Abstract: Oxidative single-electron transfer-catalyzed tandem reactions consisting of a conjugate addition and a radical cyclization are reported, which incorporate the mandatory terminal oxidant as a functionality into the product.

Cited by 51 publications

References 46 publications

Facile and Highly Diastereoselective Synthesis of syn‐ and cis‐1,2‐Diol Derivatives from Protected α‐Hydroxy Ketones

Facile and Highly Diastereoselective Synthesis of syn‐ and cis‐1,2‐Diol Derivatives from Protected α‐Hydroxy Ketones

Highly Functionalized Cyclopentane Derivatives by Tandem Michael Addition/Radical Cyclization/Oxygenation Reactions

Der “Persistent Radical Effect” in der organischen Chemie

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