Single‐Electron Transfer Reactions Enabled by N‐Heterocyclic Carbene Organocatalysis

Chemistry - A European Journal, Journal Year: 2020, Volume and Issue: 27(10), P. 3238 - 3250

Published: Oct. 9, 2020

Abstract Over the past decades, N‐heterocyclic carbene (NHC) organocatalysis has undergone a flourish of development on basis closed‐shell reaction paths. By contrast, emerging area single‐electron transfer (SET) reactions enabled by NHC catalysis still remain underdeveloped, but offer plenty opportunities to develop new catalytic modes and useful synthetic methods. A number interesting transformations were triggered SET process from electron‐rich Breslow intermediates various acceptors. In additions, recent studies revealed that radical cations could also be generated reduction electron‐deficient acyl azolium intermediates. These discoveries open avenue for harness reactions. The present review will focus exciting advancements in dynamic organocatalysis.

Language: Английский

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Critical Assessment of the Reducing Ability of Breslow‐type Derivatives and Implications for Carbene‐Catalyzed Radical Reactions**

Angewandte Chemie International Edition, Journal Year: 2021, Volume and Issue: 60(51), P. 26783 - 26789

Published: Oct. 15, 2021

Abstract We report the synthesis of acyl azolium salts stemming from thiazolylidenes C NS , triazolylidenes TN mesoionic carbenes MIC and generation their corresponding radicals enolates, covering about 60 Breslow‐type derivatives. This study highlights role additives in redox behavior these compounds unveils several critical misconceptions radical transformations aldehyde derivatives under N‐heterocyclic carbene catalysis. In particular, reducing ability enolates has been dramatically underestimated case biomimetic . contrast with previous electrochemical studies, we show that catalytic intermediates can transfer electrons to iodobenzene within minutes at room temperature. Enols derived are not previously claimed super electron donors, although enolate powerful agents.

Language: Английский

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1,4-Alkylcarbonylation of 1,3-Enynes to Access Tetra-Substituted Allenyl Ketones via an NHC-Catalyzed Radical Relay

ACS Catalysis, Journal Year: 2021, Volume and Issue: 11(21), P. 13363 - 13373

Published: Oct. 19, 2021

Reactions involving allenyl ion intermediates have been widely applied in the synthesis of functionalized allenes, but reactions radicals less studied and limited successful examples realized mainly by transition metal catalysis. We herein demonstrate generation N-heterocyclic carbene (NHC) organocatalysis their applications three-component radical relay 1,4-alkylcarbonylation 1,3-enynes without participation. This strategy could accommodate a collection different alkyl precursors such as CF3I, halides, cycloketone oxime esters, aliphatic carboxylic acid derived redox-active enabling convenient pathway to access range synthetically challenging tetra-substituted ketones with high regioselectivity. The key success this protocol relied on Csp-C(O)sp2 radical–radical coupling NHC-bound ketyl radicals, constructing ketone motifs highly efficient reaction pathway.

Language: Английский

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Recent Advances in Theoretical Studies on Transition-Metal-Catalyzed Carbene Transformations

Accounts of Chemical Research, Journal Year: 2021, Volume and Issue: 54(14), P. 2905 - 2915

Published: July 7, 2021

ConspectusMetal carbene plays a vital role in modern organic synthesis. The neutral divalent carbon of metal renders it an active intermediate throughout range reactions. In experiments, diverse carbene-related transformation reactions have been established, including transition-metal-catalyzed cross-coupling using N-heterocyclic carbenes as ligands, insertion into σ bonds, cyclopropanations, ylide formation, and so forth. remarkable progress achieved synthetic chemistry, turn, has increased the demand for mechanistic studies chemistry. A thorough understanding reaction mechanisms can extend application scope compounds inspire rational design new reactions.Density functional theory (DFT) calculations performed our group to gain more insights This account focuses on computational with nucleophiles. generation or metal-ligated free subsequent pathways is discussed. According nucleophiles, three generalized models are summarized, intramolecular migratory carbene, intermolecular nucleophilic addition toward outer-sphere carbene.In general, mechanism commonly proposed since electrophilic carbon. From point view, also widely used because bonds formally occurs through this mechanism. An that form complex instead carbene. contains naked not coordinated center. case, transition-metal catalyst only Lewis acid, directly at Our results suggested facile step ligation could stabilize transition state well generated intermediate. low energy barrier due lack entropy penalty. Carbene formation from precursors usually rate-determining step, except addition, reactivity nucleophiles significant influence overall rate. We envision weak nucleophilicity would suppress addition. These showcase characteristics models, we hope will spur development

Language: Английский

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Catalytic, Metal-Free Amide Synthesis from Aldehydes and Imines Enabled by a Dual-Catalyzed Umpolung Strategy under Redox-Neutral Conditions

ACS Catalysis, Journal Year: 2020, Volume and Issue: 10(21), P. 12960 - 12966

Published: Oct. 22, 2020

The synthesis of amides is a long-term theme in chemistry and related areas. use readily available cost-effective precursors for straightforward amide with atom economy under mild conditions attractive yet challenging. Herein, we report the direct from aldehydes imines 100% atom-economical manner. redox-neutral C–N bond-forming process was enabled by dual catalysis visible light an N-heterocyclic carbene (NHC) at room temperature. This protocol features unprecedented umpolung to generate N-centered radicals. Mechanistic investigations reveal this reaction undergoes nontrivial radical–radical coupling between radical C-centered forge bond. operationally simple tolerates wide range functional groups, providing rapid access aromatic or aliphatic without producing any byproduct.

Language: Английский

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Catalytic Generation of Carbanions through Carbonyl Umpolung

Angewandte Chemie International Edition, Journal Year: 2021, Volume and Issue: 60(40), P. 21624 - 21634

Published: May 15, 2021

Abstract Carbonyl Umpolung is a powerful strategy in organic chemistry to construct complex molecules. Over the last few years, versatile catalytic approaches for generation of acyl anion equivalents from carbonyl compounds have been developed, but methods obtain alkyl carbanions fashion are still at an early stage. This Minireview summarizes recent progress through Umpolung. Two different can be utilized enable compounds: Wolff–Kishner reaction and single‐electron reduction imines. We discuss scope, mechanistic insights, synthetic applications as well potential future developments.

Language: Английский

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N-Heterocyclic carbene (NHC) organocatalysis using aliphatic aldehydes

Chemical Communications, Journal Year: 2020, Volume and Issue: 56(99), P. 15484 - 15495

Published: Jan. 1, 2020

Recent advances are presented in NHC catalysis employing aliphatic aldehydes as substrates for the generation of various carbene-bound intermediates and subsequent interception with electrophiles/nucleophiles.

Language: Английский

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Suzuki-type cross-coupling of alkyl trifluoroborates with acid fluoride enabled by NHC/photoredox dual catalysis

Chemical Science, Journal Year: 2022, Volume and Issue: 13(9), P. 2584 - 2590

Published: Jan. 1, 2022

An acylative Suzuki-type cross-coupling of alkyl trifluoroborates and acid fluorides was developed by merging NHC organocatalysis with photoredox catalysis. A broad spectrum ketones could be facilely synthesised under mild reaction conditions.

Language: Английский

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Recent advances in transition-metal-free trifluoromethylation with Togni's reagents

Organic Chemistry Frontiers, Journal Year: 2021, Volume and Issue: 9(4), P. 1152 - 1164

Published: Dec. 16, 2021

Transition-metal-free trifluoromethylations have attracted significant research interest driven by the increasing importance of CF 3 -containing compounds.

Language: Английский

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N-Heterocyclic carbenes and their precursors in functionalised porous materials

Chemical Society Reviews, Journal Year: 2021, Volume and Issue: 50(24), P. 13559 - 13586

Published: Jan. 1, 2021

Though N-heterocyclic carbenes (NHCs) have emerged as diverse and powerful discrete functional molecules in pharmaceutics, nanotechnology, catalysis over decades, the heterogenization of NHCs their precursors for broader applications porous materials, like metal-organic frameworks (MOFs), coordination polymers (PCPs), covalent-organic (COFs), organic (POPs), organometallic cages (POMCs) was not extensively studied until last ten years. By de novo or post-synthetic modification (PSM) methods, myriads containing building blocks were designed integrated into MOFs, PCPs, COFs, POPs POMCs to form various structures porosities. Functionalisation with significantly expands scope potential materials by tuning pore surface chemical/physical properties, providing active sites binding guest substrates realizing recyclability. In this review, we summarise discuss recent progress on synthetic structural features, promising functionalised materials. At end, a brief perspective encouraging future prospects challenges contemporary field is presented. This review will serve guide researchers design synthesize more novel precursors.

Language: Английский

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