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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Non-innocent Radical Ion Intermediates in Photoredox Catalysis: Parallel Reduction Modes Enable Coupling of Diverse Aryl Chlorides

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(29), P. 10882 - 10889

Published: July 13, 2021

We describe a photocatalytic system that elicits potent photoreductant activity from conventional photocatalysts by leveraging radical anion intermediates generated in situ. The combination of an isophthalonitrile photocatalyst and sodium formate promotes diverse aryl coupling reactions abundant but difficult to reduce chloride substrates. Mechanistic studies reveal two parallel pathways for substrate reduction both enabled key terminal reductant byproduct, carbon dioxide anion.

Language: Английский

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Copper-catalysed amination of alkyl iodides enabled by halogen-atom transfer

Nature Catalysis, Journal Year: 2021, Volume and Issue: 4(7), P. 623 - 630

Published: July 12, 2021

Language: Английский

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Late‐Stage Heteroarylation of Hetero(aryl)sulfonium Salts Activated by α‐Amino Alkyl Radicals

Angewandte Chemie International Edition, Journal Year: 2021, Volume and Issue: 60(24), P. 13609 - 13613

Published: April 9, 2021

We report a late-stage heteroarylation of aryl sulfonium salts through activation with α-amino alkyl radicals in mechanistically distinct approach from previously reported halogen-atom transfer (XAT). The new mode proceeds the absence light and photoredox catalysts, engaging wide range hetarenes. Furthermore, we demonstrate applicability this methodology synthetically useful cross-coupling transformations.

Language: Английский

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Halogen-atom and group transfer reactivity enabled by hydrogen tunneling

Science, Journal Year: 2022, Volume and Issue: 377(6612), P. 1323 - 1328

Published: Sept. 15, 2022

The generation of carbon radicals by halogen-atom and group transfer reactions is generally achieved using tin silicon reagents that maximize the interplay enthalpic (thermodynamic) polar (kinetic) effects. In this work, we demonstrate a distinct reactivity mode enabled quantum mechanical tunneling uses cyclohexadiene derivative γ-terpinene as abstractor under mild photochemical conditions. This protocol activates alkyl aryl halides well several alcohol thiol derivatives. Experimental computational studies unveiled noncanonical pathway whereby cyclohexadienyl radical undergoes concerted aromatization or abstraction through an effective H atom. activation mechanism seemingly thermodynamically kinetically unfavorable but rendered feasible tunneling.

Language: Английский

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CdS Quantum Dots as Potent Photoreductants for Organic Chemistry Enabled by Auger Processes

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 144(27), P. 12229 - 12246

Published: June 30, 2022

Strong reducing agents (<−2.0 V vs saturated calomel electrode (SCE)) enable a wide array of useful organic chemistry, but suffer from variety limitations. Stoichiometric metallic reductants such as alkali metals and SmI2 are commonly employed for these reactions; however, considerations including expense, ease use, safety, waste generation limit the practicality methods. Recent approaches utilizing energy multiple photons or electron-primed photoredox catalysis have accessed reduction potentials equivalent to Li0 shown how this enables selective transformations aryl chlorides via radicals. However, in some cases, low stability catalytic intermediates can turnover numbers. Herein, we report ability CdS nanocrystal quantum dots (QDs) function strong photoreductants present evidence that highly electron is generated two consecutive photoexcitations QDs with intermediate reductive quenching. Mechanistic experiments suggest Auger recombination, photophysical phenomenon known occur photoexcited anionic QDs, generates transient thermally excited electrons observed reductions. Using blue light-emitting diodes (LEDs) sacrificial amine reductants, phosphate esters up −3.4 SCE photoreductively cleaved afford hydrodefunctionalized functionalized products. In contrast small-molecule catalysts, stable under conditions numbers 47 500 been achieved. These also effect other challenging reductions, tosylate protecting group removal amines, debenzylation benzyl-protected alcohols, ring opening cyclopropane carboxylic acid derivatives.

Language: Английский

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General and Modular Route to (Halo)alkyl BCP-Heteroaryls Enabled by α-Aminoalkyl Radical-Mediated Halogen-Atom Transfer

ACS Catalysis, Journal Year: 2023, Volume and Issue: 14(2), P. 619 - 627

Published: Dec. 28, 2023

Synthesis of bicyclo[1.1.1]pentane (BCP) heteroaryls continues to be a part the most important tasks in organic synthesis because they are significant class bioisosteres with universal applications drug discovery. However, substrate scope current multicomponent reactions is limited tertiary alkyl radicals and prefunctionalized (het)arenes due their intrinsic mechanisms, resulting decrease application value. Herein, we report straightforward alternative for (halo)alkyl BCP-heteroaryls from [1.1.1]propellane enabled by α-aminoalkyl radical-mediated halogen-atom transfer (XAT). Carbon derived commonly available precursors such as primary, secondary, halides polyhalides perform additions onto give BCP radicals, which then engage C–H/C–C couplings different heteroarenes. A wide range easily constructed moderate-to-good yields. Late-stage functionalization performed on approved derivatives proceeds good efficiency produce corresponding BCP-heteroaryls. The control experiments density functional theory (DFT) calculations reveal radical nature reaction. This approach not only verifies (XAT) strategy but also provides practical efficient route multifunctionalized BCPs, significantly expands BCP-heteroaryl-type development.

Language: Английский

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Electrochemical Activation of Diverse Conventional Photoredox Catalysts Induces Potent Photoreductant Activity**

Angewandte Chemie International Edition, Journal Year: 2021, Volume and Issue: 60(39), P. 21418 - 21425

Published: July 20, 2021

Herein, we disclose that electrochemical stimulation induces new photocatalytic activity from a range of structurally diverse conventional photocatalysts. These studies uncover electron-primed photoredox catalyst capable promoting the reductive cleavage strong C(sp2 )-N and )-O bonds. We illustrate several examples synthetic utility these deeply reducing but otherwise safe mild catalytic conditions. Finally, employ current measurements to perform reaction progress kinetic analysis. This technique reveals improved this system is consequence an enhanced stability profile.

Language: Английский

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Polysulfide Anions as Visible Light Photoredox Catalysts for Aryl Cross-Couplings

Journal of the American Chemical Society, Journal Year: 2020, Volume and Issue: 143(1), P. 481 - 487

Published: Dec. 23, 2020

Polysulfide anions are endowed with unique redox properties, attracting considerable attentions for their applications in alkali metals–sulfur batteries. However, the employment of these anionic species catalysis small molecule synthesis remains underdeveloped due to moderate–poor electrochemical potential ground state, whereas some them characterized by photoabsorptions visible spectral regions. Herein, we disclose use polysulfide as light photoredox catalysts aryl cross-coupling reactions. The reaction design enables single-electron reduction halides upon photoexcitation tetrasulfide dianions (S42–). resulting radicals engaged (hetero)biaryl cross-coupling, borylation, and hydrogenation a catalytic regime involving S4• –/S42– S3• –/S32– couples.

Language: Английский

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Photoinduced Halogen-Atom Transfer by N-Heterocyclic Carbene-Ligated Boryl Radicals for C(sp³)–C(sp³) Bond Formation

Journal of the American Chemical Society, Journal Year: 2022, Volume and Issue: 145(2), P. 991 - 999

Published: Dec. 30, 2022

Herein, we present a comprehensive study on the use of N-heterocyclic carbene (NHC)-ligated boryl radicals to enable C(sp3)–C(sp3) bond formation under visible-light irradiation via Halogen-Atom Transfer (XAT). The methodology relies an acridinium dye generate boron-centered from corresponding NHC-ligated boranes single-electron transfer (SET) and deprotonation. These subsequently engage with alkyl halides in XAT step, delivering desired nucleophilic radicals. strategy is very mild accommodates broad scope halides, including medicinally relevant compounds biologically active molecules. key role operative reaction mechanism has been elucidated through combination experimental, spectroscopic, computational studies. This stands as significant advancement chemistry radicals, which had long restricted radical reductions, enabling C–C photoredox conditions.

Language: Английский

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