Catalytic hydrogen atom transfer to alkenes: a roadmap for metal hydrides and radicals

Chemical Science, Год журнала: 2020, Номер 11(46), С. 12401 - 12422

Опубликована: Янв. 1, 2020

Hydrogen atom transfer from metal hydrides to alkenes appears underlie widely used catalytic methods – the mechanistic implications are fascinating.

Язык: Английский

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A Triple Photoredox/Cobalt/Brønsted Acid Catalysis Enabling Markovnikov Hydroalkoxylation of Unactivated Alkenes

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(18), С. 7953 - 7959

Опубликована: Апрель 27, 2022

We demonstrate Markovnikov hydroalkoxylation of unactivated alkenes using alcohols through a triple catalysis consisting photoredox, cobalt, and Brønsted acid catalysts under visible light irradiation. The realizes three key elementary steps in single catalytic cycle: (1) Co(III) hydride generation by photochemical reduction Co(II) followed protonation, (2) metal hydrogen atom transfer (MHAT) hydride, (3) oxidation the alkyl complex to Co(IV). precise control protons electrons allows elimination strong acids external reductants/oxidants that are required conventional methods.

Язык: Английский

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Photo‐ and Electrochemical Cobalt Catalysed Hydrogen Atom Transfer for the Hydrofunctionalisation of Alkenes

Angewandte Chemie International Edition, Год журнала: 2023, Номер 62(41)

Опубликована: Май 15, 2023

Catalytic hydrogen atom transfer from metal-hydrides to alkenes allows feedstock olefins be used as alkyl radical precursors. The chemoselectivity of this process makes it an attractive synthetic tool and such has been regularly in synthesis complex molecules. However, onwards reactivity is limited by compatibility with the conditions which form key metal-hydride species. Now, through merger photocatalysis or electrochemistry, milder methods are emerging can unlock entirely new offer perspectives on expanding these unprecedented directions. This review outlines most recent developments electro- photochemical cobalt catalysed offers suggestions future outlook.

Язык: Английский

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Electrocatalytic Access to Azetidines via Intramolecular Allylic Hydroamination: Scrutinizing Key Oxidation Steps through Electrochemical Kinetic Analysis

Journal of the American Chemical Society, Год журнала: 2023, Номер 145(28), С. 15360 - 15369

Опубликована: Июль 10, 2023

Azetidines are prominent structural scaffolds in bioactive molecules, medicinal chemistry, and ligand design for transition metals. However, state-of-the-art methods cannot be applied to intramolecular hydroamination of allylic amine derivatives despite their underlying potential as one the most prevalent synthetic precursors azetidines. Herein, we report an electrocatalytic method sulfonamides access azetidines first time. The merger cobalt catalysis electricity enables regioselective generation key carbocationic intermediates, which could directly undergo C-N bond formation. mechanistic investigations including electrochemical kinetic analysis suggest that either catalyst regeneration by nucleophilic cyclization or second oxidation intermediate is involved rate-determining step (RDS) our protocol highlight ability electrochemistry providing ideal means mediate oxidation.

Язык: Английский

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Mechanism of Alkene Hydrofunctionalization by Oxidative Cobalt(salen) Catalyzed Hydrogen Atom Transfer

Journal of the American Chemical Society, Год журнала: 2024, Номер 146(4), С. 2685 - 2700

Опубликована: Янв. 16, 2024

Oxidative MHAT hydrofunctionalization of alkenes provides a mild cobalt-catalyzed route to forming C–N and C–O bonds. Here, we characterize relevant salen-supported cobalt complexes their reactions with alkenes, silanes, oxidant, solvent. These stoichiometric investigations are complemented by kinetic studies the catalytic reaction catalyst speciation. We describe solution characterization an elusive cobalt(III) fluoride complex, which surprisingly is not species that reacts silane under conditions; rather, aquo complex more active. Accordingly, addition water (0.15 M) speeds reaction, show enables product formation in 2 h at −50 °C acetone. Under these conditions, resting states can be observed UV–vis spectrophotometry, including cobalt(III)-alkyl complex. It comes from transient hydride formed turnover-limiting step cycle. This readily degrades but H2; it releases H+ through bimetallic pathway explains [Co]2 dependence off-cycle reaction. In contrast, rate follows power law kobs[Co]1[silane]1. Because different [Co] degradation lower loading improves yield reducing relative unproductive silane/oxidant consumption. illuminate mechanistic details oxidative lay groundwork for understanding other mediated alkyl complexes.

Язык: Английский

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Photo‐ and Cobalt‐Catalyzed Synthesis of Heterocycles via Cycloisomerization of Unactivated Olefins

Angewandte Chemie International Edition, Год журнала: 2024, Номер 63(19)

Опубликована: Фев. 28, 2024

Abstract We report a general, intramolecular cycloisomerization of unactivated olefins with pendant nucleophiles. The reaction proceeds under mild conditions and tolerates ethers, esters, protected amines, acetals, pyrazoles, carbamates, arenes. It is amenable to N ‐, O as well C ‐nucleophiles, yielding number different heterocycles including, but not limited to, pyrrolidines, piperidines, oxazolidinones, lactones. Use both benzothiazinoquinoxaline organophotocatalyst Co‐salen catalyst obviates the need for stoichiometric oxidant or reductant. showcase utility protocol in late‐stage drug diversification synthesis several small natural products.

Язык: Английский

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Iron and cobalt catalysis: new perspectives in synthetic radical chemistry

Chemical Society Reviews, Год журнала: 2020, Номер 49(23), С. 8501 - 8542

Опубликована: Янв. 1, 2020

Iron and cobalt complexes are at the origin of high valuable synthetic pathways involving radical intemediates.

Язык: Английский

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Catalytic Asymmetric Radical–Polar Crossover Hydroalkoxylation

Journal of the American Chemical Society, Год журнала: 2019, Номер 141(44), С. 17527 - 17532

Опубликована: Окт. 23, 2019

Asymmetric intramolecular hydrofunctionalization of tertiary allylic alcohols is described. This metal hydride-mediated catalytic radical–polar crossover reaction delivers corresponding epoxides in good to high enantioselectivity and constitutes the first example asymmetric hydrogen atom transfer-initiated process. A series modified cobalt salen complexes has proven optimal for achieving efficiency induction. Experimental data suggest that cationic may be involved enantiodetermining step, where cation−π interactions catalyst contribute

Язык: Английский

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Ligand-promoted cobalt-catalyzed radical hydroamination of alkenes

Nature Communications, Год журнала: 2020, Номер 11(1)

Опубликована: Фев. 7, 2020

Highly regio- and enantioselective intermolecular hydroamination of alkenes is a challenging process potentially leading to valuable chiral amines. Hydroamination via metal-catalyzed hydrogen atom transfer (HAT) with good regioselectivity functional group tolerance has been reported, however, high enantioselectivity not achieved due the lack suitable ligands. Here we report ligand-promoted cobalt-catalyzed Markovnikov-type selective radical diazo compounds. This operationally simple protocol uses unsymmetric NNN-tridentate (UNT) ligand, readily available hydrosilanes construct hydrazones tolerance. The can undergo nitrogen-nitrogen bond cleavage smoothly deliver amine derivatives. Additionally, asymmetric unactivated aliphatic terminal using N-imidazolinylphenyl 8-aminoquinoline (IPAQ) ligands also afford derivatives enantioselectivities.

Язык: Английский

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Catalyst- and Silane-Controlled Enantioselective Hydrofunctionalization of Alkenes by Cobalt-Catalyzed Hydrogen Atom Transfer and Radical-Polar Crossover

Journal of the American Chemical Society, Год журнала: 2020, Номер 142(31), С. 13481 - 13490

Опубликована: Июль 10, 2020

The catalytic enantioselective synthesis of tetrahydrofurans, which are found in the structures many biologically active natural products, via a transition-metal-catalyzed hydrogen atom transfer (TM-HAT) and radical-polar crossover (RPC) mechanism is described herein. Hydroalkoxylation nonconjugated alkenes proceeded efficiently with excellent enantioselectivity (up to 94% ee) using suitable chiral cobalt catalyst, N-fluoro-2,4,6-collidinium tetrafluoroborate, diethylsilane. Surprisingly, absolute configuration product was highly dependent on steric hindrance silane. Slow addition silane, dioxygen effect solvent, thermal dependence, DFT calculation results supported unprecedented scenario two competing selective mechanisms. For less-hindered diethylsilane, high concentration diffused carbon-centered radicals invoked diastereoenrichment an alkylcobalt(III) intermediate by radical chain reaction, eventually determined product. On other hand, more hindered silane resulted less opportunity for instead facilitating kinetic resolution during late-stage nucleophilic displacement alkylcobalt(IV) intermediate.

Язык: Английский

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