Catalytic Reductive Cross Coupling and Enantioselective Protonation of Olefins to Construct Remote Stereocenters for Azaarenes

Kong, Manman; Tan, Yaqi; Zhao, Xiaowei; Qiao, Baokun; Tan, Choon‐Hong; Cao, Shanshan; Jiang, Zhiyong

doi:10.1021/jacs.1c01073

Cited by 84 publications

(45 citation statements)

References 57 publications

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“…reported chiral phosphoric acid/photocatalytic asymmetric reductive cross‐coupling between α‐branched vinylketones and vinylazaarenes (Scheme 80). [152] The novelty of the reaction is that highly enantioenriched δ‐stereocenters were formed during the enantioselective protonation step with satisfactory regioselectivity and chemoselectivity. A diverse array of enantioenriched azaarenes were obtained in 35 %–95 % yields and 62 %–99 % ee.…”

Section: Photoredox/chiral Brønsted Acid/base Dual Catalysismentioning

confidence: 99%

“… Catalytic reductive cross‐coupling of α‐branched vinylketones with vinylazaarenes to construct δ‐stereocenters and 1,4‐sterocentres [152] …”

Section: Photoredox/chiral Brønsted Acid/base Dual Catalysismentioning

confidence: 99%

“… Proposed mechanism for catalytic reductive cross‐coupling of α‐branched vinylketones with vinylazaarenes [152] …”

Section: Photoredox/chiral Brønsted Acid/base Dual Catalysismentioning

confidence: 99%

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Asymmetric Photocatalysis Enabled by Chiral Organocatalysts

2021

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Visible‐light photocatalysis has advanced as a versatile tool in organic synthesis. However, attaining precise stereocontrol in photocatalytic reactions has been a longstanding challenge due to undesired photochemical background reactions and the involvement of highly reactive radicals or radical ion intermediates generated under photocatalytic conditions. To address this problem and expand the synthetic utility of photocatalytic reactions, a number of innovative strategies, including mono‐ and dual‐catalytic approaches, have recently emerged. Of these, exploiting chiral organocatalysis, such as enamine catalysis, iminium‐ion catalysis, Brønsted acid/base catalysis, and N‐heterocyclic carbene catalysis, to induce chirality transfer of photocatalytic reactions has been widely explored. This Review aims to provide a current, comprehensive overview of asymmetric photocatalytic reactions enabled by chiral organocatalysts published through June 2021. The substrate scope, advantages, limitations, and proposed reaction mechanisms of each reaction are discussed. This review should serve as a reference for the development of visible‐light‐induced asymmetric photocatalysis and promote the improvement of the chemical reactivity and stereoselectivity of these reactions.

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Section: Photoredox/chiral Brønsted Acid/base Dual Catalysismentioning

confidence: 99%

“… Catalytic reductive cross‐coupling of α‐branched vinylketones with vinylazaarenes to construct δ‐stereocenters and 1,4‐sterocentres [152] …”

Section: Photoredox/chiral Brønsted Acid/base Dual Catalysismentioning

confidence: 99%

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Asymmetric Photocatalysis Enabled by Chiral Organocatalysts

2021

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“…The reductive PCET of C＝C bonds in α,β-unsaturated carbonyl compounds can also be followed by the formation of a new C-C bond via a radical addition to another alkenes. In 2021, Jiang's group [131] reported a novel strategy in order to access the enantioselective protonation that is triggered by the reductive cross coupling of olefin substrates (Scheme 57). Through this method, under the reaction conditions consist of cooperative photoredox and chiral hydrogen-bonding catalyst, in addition of a terminal reductant, a diverse range of enantioenriched azaarene products with tertiary stereocenters at their δ-position, which are important structures commonly exist in many natural products, could be generated from the corresponding α-branched vinylketones in both high yield and ee.…”

Section: Oxidative Decarboxylationmentioning

confidence: 99%

Applications of Proton-Coupled Electron Transfer in Organic Synthesis

Zhou¹,

Kong²,

Liu³

2021

Chinese Journal of Organic Chemistry

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Proton-coupled electron transfer (PCET) reactions are a kind of unconventional redox reactions, which exhibit special reactivities and selectivities due to their unique interdependent electron-proton transfer mechanisms. There are three possible pathways of PCET processes, including stepwise electron transfer followed by proton transfer (ETPT), proton transfer followed by electron transfer (PTET), and concerted pathway in which electron and proton transfer synchronously (CEPT), avoiding intermediates with high energy. These reactions have been playing a key role in numerous areas in organic chemistry, inorganic chemistry, bioorganic chemistry, organometallic and material chemistry, including the redox processes in natural and artificial systems, such as the activation for small molecules. Recently, the application of PCET reactions in organic synthesis has received a great deal of attentions and interests. Being accompanied by the development of electrochemical methods and photocatalysts, more and more novel reactions in electrochemistry and photochemistry involve PCET processes have been reported. Applying these electrochemical and photochemical methods, the activation of X-H bond has been achieved via PCET processes, including C-H bond, N-H bond, P-H bond, S-H bond or O-H bond. Thus, based on these crucial processes, a number of vital structures and fundamental frameworks can be synthesized, and various synthetic building blocks and natural products have been attained. For example, pharmaceutical building blocks like 2°-piperidines can be cyanated at their α-position; substituted dimeric pyrroloindolines such as (-)-calycanthidine, (-)-chimonanthine, and (-)-psychotriasine have also been successfully synthesized via PCET mechanism. Moreover, not only the products of reduction of multiple bonds (C＝ Y bond such as C＝C bond, C＝N bond and C＝O bond), but also the products of self/cross-coupling have been achieved via PCET mechanism. In this review, the recent applications and developments of PCET mechanism in organic synthesis are summarized, including new catalyst systems and new reagents, especially with electrochemical and photochemical methodologies. The future of this area has also been demonstrated from both experimental and theoretical aspects. Keywords proton-coupled electron transfer; organic synthesis; radical reactions; functionalization

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“…Subsequently, many elegant studies revealed that bifunctional H‐bonding catalysis, that is, with acid and base moieties of chiral catalysts interacting with radicals and reaction partners simultaneously, is more versatile (Scheme 1C) [3, 7] . Among them, our group successfully developed a range of important enantioselective radical addition and radical coupling reactions, [7d–i] in which the construction of enantioenriched imine‐containing azaarene variants was closely watched given the ubiquity of azaarenes in natural products, pharmaceuticals and functional materials. Accordingly, we were interested in tackling the challenging Melchiorre reaction, and N ‐phenylglycine was used as the precursor of the α‐amino radical because it features a H‐bond donor (see below).…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Hydroaminoalkylation of Alkenylazaarenes via Cooperative Photoredox and Chiral Hydrogen‐Bonding Catalysis

Chai

Zhao

et al. 2022

Angewandte Chemie

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Chiral hydrogen‐bonding (H‐bonding) catalytic asymmetric conjugate addition to activated olefins has been widely used to access enantioenriched molecules containing stereocenters at the β‐position of the olefin activating groups. Herein, we report the first highly enantioselective radical‐based manifold. Under a dual organocatalyst system involving a chiral phosphoric acid and DPZ as the photoredox sensitizer, transformations of N‐arylglycines, in which aryls with CF3 substituents are introduced, with alkenyl azaarenes afforded valuable hydroaminoalkylation adducts with satisfactory results. In addition to the diversity of azaarenes, the method can be used to construct aryl‐, alkyl‐ and silyl‐substituted stereocenter. Control experiments and density functional theory calculations were performed to elucidate a plausible reaction mechanism and the origin of stereoselectivity, wherein nonclassical H‐bonding interactions were found to assist chiral catalysts in offering sufficient enantiocontrol.

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Catalytic Reductive Cross Coupling and Enantioselective Protonation of Olefins to Construct Remote Stereocenters for Azaarenes

Cited by 84 publications

References 57 publications

Asymmetric Photocatalysis Enabled by Chiral Organocatalysts

Asymmetric Photocatalysis Enabled by Chiral Organocatalysts

Applications of Proton-Coupled Electron Transfer in Organic Synthesis

Asymmetric Hydroaminoalkylation of Alkenylazaarenes via Cooperative Photoredox and Chiral Hydrogen‐Bonding Catalysis

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