The Persistent Radical Effect in Organic Synthesis

Angewandte Chemie International Edition, Journal Year: 2019, Volume and Issue: 59(1), P. 74 - 108

Published: May 22, 2019

Abstract Radical–radical couplings are mostly nearly diffusion‐controlled processes. Therefore, the selective cross‐coupling of two different radicals is challenging and not a synthetically valuable transformation. However, if have lifetimes they generated at equal rates, will become dominant process. This high cross‐selectivity based on kinetic phenomenon called persistent radical effect (PRE). In this Review, an explanation PRE supported by simulations simple model systems provided. Radical stabilities discussed within context their lifetimes, various examples PRE‐mediated radical–radical in synthesis summarized. It shown that restricted to coupling with transient radical. If one partner longer‐lived than other radical, operates achieved. important point expands scope chemistry. The Review divided into parts, namely 1) or organic 2) “radical–metal crossover reactions”; here, metal‐centered species more generally transition‐metal complexes able react discussed—a field has flourished recently.

Language: Английский

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Nickel-Catalyzed Enantioselective Reductive Cross-Coupling Reactions

ACS Catalysis, Journal Year: 2020, Volume and Issue: 10(15), P. 8237 - 8246

Published: June 24, 2020

Nickel-catalyzed reductive cross-coupling reactions have emerged as powerful methods to join two electrophiles. These proven particularly useful for the coupling of sec-alkyl electrophiles form stereogenic centers; however, development enantioselective variants remains challenging. In this Perspective, we summarize progress that has been made toward Ni-catalyzed reactions.

Language: Английский

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Mechanisms of Nickel-Catalyzed Cross-Coupling Reactions

Trends in Chemistry, Journal Year: 2019, Volume and Issue: 1(9), P. 830 - 844

Published: Sept. 13, 2019

Language: Английский

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Applications of Halogen-Atom Transfer (XAT) for the Generation of Carbon Radicals in Synthetic Photochemistry and Photocatalysis

Chemical Reviews, Journal Year: 2021, Volume and Issue: 122(2), P. 2292 - 2352

Published: Dec. 9, 2021

The halogen-atom transfer (XAT) is one of the most important and applied processes for generation carbon radicals in synthetic chemistry. In this review, we summarize highlight aspects associated with XAT impact it has had on photochemistry photocatalysis. organization material starts analysis mechanistic then follows a subdivision based nature reagents used halogen abstraction. This review aims to provide general overview fundamental concepts main agents involved objective offering tool understand facilitate development new radical strategies.

Language: Английский

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Nickel-Catalyzed Dicarbofunctionalization of Alkenes

ACS Catalysis, Journal Year: 2020, Volume and Issue: 10(15), P. 8542 - 8556

Published: July 2, 2020

1,2-Dicarbofunctionalization of alkenes has emerged as an efficient synthetic strategy for preparing substituted molecules by coupling readily available with electrophiles and/or nucleophiles. Nickel complexes serve effective catalysts owing to their tendency undergo facile oxidative addition and slow β-hydride elimination, capability access both two-electron radical pathways. Two-component alkene functionalization reactions have achieved high chemo-, regio-, stereoselectivities tethering one the partners substrate. Three-component reactions, however, often incorporate directing groups control selectivity. Only a few examples directing-group-free difunctionalizations unactivated been reported. Therefore, great opportunities exist development three-component difunctionalization broad substrate scopes tunable stereoselectivities.

Language: Английский

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Mechanisms of Nickel-Catalyzed Coupling Reactions and Applications in Alkene Functionalization

Accounts of Chemical Research, Journal Year: 2020, Volume and Issue: 53(4), P. 906 - 919

Published: April 2, 2020

ConspectusNickel complexes exhibit distinct properties from other group 10 metals, including a small nuclear radius, high paring energy, low electronegativity, and redox potentials. These enable Ni catalysts to accommodate stabilize paramagnetic intermediates, access radical pathways, undergo slow β-H elimination. Our research program investigates how each of these fundamental attributes impact the catalytic Ni, in particular context alkene functionalization.Alkenes are versatile functional groups, but stereoselective carbofunctionalization reactions alkenes have been underdeveloped. This challenge may derive difficulty controlling selectivity via traditional two-electron migratory insertion pathways. could lead different stereodetermining steps mechanisms, allowing molecular scaffolds that otherwise difficult prepare. For example, an asymmetric diarylation reaction developed by our relies upon Ni(III) intermediates control enantioselectivity give library chiral α,α,β-triarylethane molecules with biological activity.Mechanistic studies on two-component reductive 1,2-difunctionalization shed light origin cross-electrophile selectivity, as C sp2 sp3 electrophiles independently activated at Ni(I) respectively. Catalyst reduction has identified be turnover-limiting step this system. A closer investigation formation using (Xantphos)Ni(I)Ar model complex reveals initiates concerted halogen-abstraction pathway.The potentials allowed us develop reductive, trans-selective diene cyclization, wherein classic mechanism operates Ni(I)/Ni(III) platform, accounting for chemo- stereoselectivity. found applications efficient synthesis pharmaceutically relevant molecules, such 3,4-dimethylgababutin.The tendency one-electron processes prompted explore dinuclear Ni-mediated bond formations. provide insight into Ni–Ni bonding two metal centers react cooperatively promote C–C, C–X, N–N forming elimination.Finally, isolation β-agostic Pd X-ray neutron diffraction characterization highly reactive molecules. The parameters serve unambiguous evidence interactions help rationalize slower elimination relative Pd. Overall, elucidated several contexts. Greater mechanistic understanding facilitates catalyst design helps reactivity Ni-catalyzed functionalization reactions.

Language: Английский

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Nickel‐Catalyzed Asymmetric Reductive Diarylation of Vinylarenes

Angewandte Chemie International Edition, Journal Year: 2019, Volume and Issue: 58(10), P. 3198 - 3202

Published: Jan. 25, 2019

Abstract A nickel‐catalyzed asymmetric diarylation reaction of vinylarenes enables the preparation chiral α,α,β‐triarylated ethane scaffolds, which exist in a number biologically active molecules. The use reducing conditions with aryl bromides as coupling partners obviates need for stoichiometric organometallic reagents and tolerates broad range functional groups. application an N ‐oxyl radical ligand to nickel catalyst represents novel approach facilitate cross‐coupling reactions.

Language: Английский

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Asymmetric Ni-Catalyzed Radical Relayed Reductive Coupling

Journal of the American Chemical Society, Journal Year: 2020, Volume and Issue: 142(31), P. 13515 - 13522

Published: June 29, 2020

Alkene dicarbofunctionalizations enable the streamlined construction of aliphatic structures and have thus been subject intense research efforts. Despite significant progress, catalytic asymmetric variants remain scarce. Inspired by advantages reductive cross-coupling approaches, we present here a highly efficient intermolecular Ni-catalyzed dicarbofunctionalization alkenes. Two distinct readily available electrophiles, namely, Csp2- Csp3-halides, are added simultaneously across variety olefins (vinyl amides, vinyl boranes, phosphonates) at room temperature in regio- enantioselective manner. The reaction, devoid sensitive organometallic reagents, takes advantage an situ generated chiral alkyl Ni(III)-intermediate to ensure stereodefined outcome Csp3–Csp2 bond-forming reaction. An (l)-(+)-isoleucine bisoxazoline ligand presence coordinating sites on alkene key for successful these "asymmetric radical relayed couplings" (ARRRCs). Further, multiple transformations amides obtained this process showcase potential new methodology straightforward assembly building blocks such as primary secondary amines oxazolines, highlighting its synthetic utility.

Language: Английский

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Electrochemically driven cross-electrophile coupling of alkyl halides

Nature, Journal Year: 2022, Volume and Issue: 604(7905), P. 292 - 297

Published: Feb. 21, 2022

Language: Английский

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Mechanism of Ni-Catalyzed Reductive 1,2-Dicarbofunctionalization of Alkenes

Journal of the American Chemical Society, Journal Year: 2019, Volume and Issue: 141(44), P. 17937 - 17948

Published: Oct. 7, 2019

Ni-catalyzed cross-electrophile coupling reactions have emerged as appealing methods to construct organic molecules without the use of stoichiometric organometallic reagents. The mechanisms are complex: plausible pathways, such "radical chain" and "sequential reduction" mechanisms, dependent on sequence activation electrophiles. A combination kinetic, spectroscopic, studies reveals that a Ni-catalyzed, reductive 1,2-dicarbofunctionalization alkenes proceeds through pathway. reduction Ni by Zn is turnover-limiting step, consistent with Ni(II) intermediates catalyst resting-state. only sufficient reduce (phen)Ni(II) Ni(I) species. As result, commonly proposed Ni(0) absent under these conditions. (Phen)Ni(I)–Br selectively activates aryl bromides via two-electron oxidation addition, whereas alkyl activated (phen)Ni(I)–Ar single-electron afford radicals. These findings could provide insight into achieving selectivity between different

Language: Английский

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