Themed collection FOCUS: Radical-involved chemical transformations
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Photoinduced strategies towards strained molecules
Photoinduced strategies towards radical reactions of [1.1.1]propellane and bicyclo [1.1.0]butanes by photoredox or metallaphotoredox catalysis have recently been disclosed, enabling controllable construction of 1,3-difunctionalized bicyclo[1.1.1]pentanes and cyclobutanes.
Org. Chem. Front., 2020,7, 2531-2537
https://doi.org/10.1039/D0QO00460J
Recent advances in phosphoranyl radical-mediated deoxygenative functionalisation
Alcohols and carboxylic acids have been established as versatile building blocks in the assembly of various carbon frameworks.
Org. Chem. Front., 2020,7, 2319-2324
https://doi.org/10.1039/D0QO00643B
Dual N-heterocyclic carbene/photocatalysis: a new strategy for radical processes
Dual N-heterocyclic carbene/photocatalysis displays unique features compared with the traditional methods and indicates high potential for new radical processes.
Org. Chem. Front., 2020,7, 2082-2087
https://doi.org/10.1039/D0QO00494D
Recent advances in cascade radical cyclization of radical acceptors for the synthesis of carbo- and heterocycles
This review is devoted to highlighting main achievements in the development of cascade radical cyclization of radical acceptors for the synthesis of carbo- and heterocycles.
Org. Chem. Front., 2021,8, 1345-1363
https://doi.org/10.1039/D0QO01453B
Nitriles as radical acceptors in radical cascade reactions
The application of the cyano group as a radical acceptor in the cascade reactions for the construction of various important heterocycles and carbocycles was summarized.
Org. Chem. Front., 2021,8, 445-465
https://doi.org/10.1039/D0QO01058H
Recent advances in nitro-involved radical reactions
Significant progress in the chemistry of nitro radicals has been witnessed in the past decades, providing efficient and rapid access to nitro-containing compounds. This review describes recent advances in nitro-involved radical reactions, and summarizes various transformations.
Org. Chem. Front., 2020,7, 2873-2898
https://doi.org/10.1039/D0QO00563K
Cooperative photoredox and chiral hydrogen-bonding catalysis
Chiral hydrogen-bonding catalysis is a classic strategy in asymmetric organocatalysis. Recently, it has been used to cooperate with photoredox catalysis, becoming a powerful tool to access optical pure compounds via radical-based transformations.
Org. Chem. Front., 2020,7, 1283-1296
https://doi.org/10.1039/D0QO00276C
Recent advances in photocatalytic C–S/P–S bond formation via the generation of sulfur centered radicals and functionalization
In this review, we have focused on the recent advances in photocatalytic C–S/P–S bond formation via the generation of thioyl/sulfonyl radicals and further functionalization.
Org. Chem. Front., 2019,6, 2048-2066
https://doi.org/10.1039/C8QO01353E
Insertion of sulfur dioxide via a radical process: an efficient route to sulfonyl compounds
This review is focused on the recent advances in the chemistry of sulfur dioxide fixation through a radical process. Diverse sulfonyl compounds can be obtained efficiently under mild conditions.
Org. Chem. Front., 2018,5, 691-705
https://doi.org/10.1039/C7QO01073G
Visible-light-driven photoredox-catalyzed C(sp3)–C(sp3) cross-coupling of N-arylamines with cycloketone oxime esters
A novel photoredox-catalyzed C(sp3)–C(sp3) cross-coupling between N-arylamines and cycloketone oxime esters under mild conditions has been accomplished.
Org. Chem. Front., 2022,9, 2534-2540
https://doi.org/10.1039/D2QO00128D
The copper-catalyzed radical aminophosphinoylation of maleimides with anilines and diarylphosphine oxides
The radical aminophosphinoylation of maleimides with anilines and diarylphosphine oxides.
Org. Chem. Front., 2022,9, 2471-2476
https://doi.org/10.1039/D2QO00184E
Providing direction for mechanistic inferences in radical cascade cyclization using a Transformer model
Transformer, a sequence-to-sequence deep learning model, is capable of predicting the reaction intermediates of radical cascade cyclization. This study provides a novel approach to help chemists discover the mechanisms of organic reactions.
Org. Chem. Front., 2022,9, 2498-2508
https://doi.org/10.1039/D2QO00188H
Direct C(sp3)–H difluoromethylation via radical–radical cross-coupling by visible-light photoredox catalysis
The first approach of photoredox catalyzed radical–radical cross-coupling difluoromethylation of C(sp3)−H bond was reported, featuring transition metal-free, good functional group tolerance, broad substrate scope and mild reaction conditions.
Org. Chem. Front., 2022,9, 2141-2148
https://doi.org/10.1039/D2QO00192F
Radical hydrotrifluoromethylation of ynamides: a route toward β-CF3 enamides
We report here a radical hydrotrifluoromethylation of ynamides to provide an alternative route toward β-CF3 enamides.
Org. Chem. Front., 2022,9, 2169-2175
https://doi.org/10.1039/D2QO00045H
Visible-light-promoted radical amidoarylation of arylacrylamides towards amidated oxindoles
A visible-light-promoted radical amidation/cyclization of arylacrylamides was realized by using N-aminopyridinium salts as the source of amidyl radicals. A variety of amide-tethered-oxindoles were prepared in this way in moderate to good yields.
Org. Chem. Front., 2022,9, 2164-2168
https://doi.org/10.1039/D2QO00127F
Planar Blatter radicals through Bu3SnH- and TMS3SiH-assisted cyclization of aryl iodides: azaphilic radical addition
Radical chain cyclization of aryl iodides provides an efficient synthesis of planar Blatter radicals, and, for the first time, access to functionalized sulphur-containing analogues.
Org. Chem. Front., 2022,9, 929-938
https://doi.org/10.1039/D1QO01742J
Alkoxycarbonyl radicals from alkyloxalyl chlorides: photoinduced synthesis of isoquinolinediones under visible light irradiation
Alkyloxalyl chlorides, generated from alcohols and oxalyl chlorides, are used as alkoxycarbonyl radicals in the reaction of N-acryloyl benzamides under photocatalysis at room temperature.
Org. Chem. Front., 2021,8, 6704-6709
https://doi.org/10.1039/D1QO01368H
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Homolysis/mesolysis of alkoxyamines activated by chemical oxidation and photochemical-triggered radical reactions at room temperature
Instantaneous and spontaneous room temperature C–ON bond mesolysis of alkoxyamines triggered by chemical oxidation.
Org. Chem. Front., 2021,8, 6561-6576
https://doi.org/10.1039/D1QO01276B
Nickel-catalyzed electrochemical reductive relay cross-coupling of alkyl halides with alkyl carboxylic acids
A highly regioselective Ni-catalyzed electrochemical (undivided cell) reductive relay cross-coupling between alkyl carboxylic acids and alkyl bromides has been developed.
Org. Chem. Front., 2021,8, 6603-6608
https://doi.org/10.1039/D1QO01219C
Radical heteroarylation of unactivated remote C(sp3)–H bonds via intramolecular heteroaryl migration
Described herein is the radical-mediated heteroarylation of unactivated remote C(sp3)–H bonds via intramolecular heteroaryl migration.
Org. Chem. Front., 2021,8, 6395-6399
https://doi.org/10.1039/D1QO01209F
N-Heterocyclic carbene-catalyzed radical ring-opening acylation of oxime esters with aldehydes
We report a radical cross-coupling of cycloketone oxime esters with aldehydes by N-heterocyclic carbene (NHC) organocatalysis. This protocol features easy operation, with no need for external redox reagent, and a broad functional group compatibility.
Org. Chem. Front., 2021,8, 6074-6079
https://doi.org/10.1039/D1QO01015H
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Radical cations and dications of bis[1]benzothieno[1,4]thiazine isomers
Radical cations and dications of three isomeric bis[1]benzothieno[1,4]thiazines are (electro)chemically generated, spectroscopically characterized and assigned by (TD)DFT calculations.
Org. Chem. Front., 2021,8, 5744-5755
https://doi.org/10.1039/D1QO00867F
Copper-catalyzed [3 + 2]/[3 + 2] carboannulation of dienynes and arylsulfonyl chlorides enabled by Smiles rearrangement: access to cyclopenta[a]indene-fused quinolinones
A radical Smiles rearrangement strategy for allowing an unprecedented [3 + 2]/[3 + 2] carboannulation of dienynes with arylsulfonyl chlorides using cheap copper catalysis is described.
Org. Chem. Front., 2021,8, 5092-5097
https://doi.org/10.1039/D1QO00703C
Construction of novel bridged aromatic ring-fused oxazocine frameworks via an N-heterocyclic carbene-catalyzed azabenzoin reaction and radical-initiated cascade cyclization
A novel method for the construction of 1,5-methanobenzo[f][1,3]oxazocin-6-ones and 6,10-methanopyrido[3,2-f][1,3]oxazocin-5-ones from o-vinyl aromatic aldehydes and N-acylarylimines was developed via NHC-catalyzed and radical-initiated reactions.
Org. Chem. Front., 2021,8, 4192-4201
https://doi.org/10.1039/D1QO00483B
Radical addition reaction between chromenols and toluene derivatives initiated by Brønsted acid catalyst under light irradiation
A Brønsted acid-catalyzed radical addition reaction between chromenols and toluene derivatives was accomplished under light irradiation, affording benzylated chromene derivatives through benzylic C(sp3)–H functionalization of toluene derivatives.
Org. Chem. Front., 2021,8, 4153-4159
https://doi.org/10.1039/D1QO00657F
Symmetric cytotoxic trimeric and dimeric indole alkaloids isolated from Bousigonia angustifolia
Symmetric trimeric and dimeric indole alkaloids were isolated for the first time from Bousigonia angustifolia, and they could be constructed through Friedel–Crafts and free radical reactions, respectively.
Org. Chem. Front., 2021,8, 2601-2607
https://doi.org/10.1039/D0QO01565B
Visible-light-promoted cross-coupling reaction of hypervalent bis-catecholato silicon compounds with selenosulfonates or thiosulfonates
A visible-light-promoted free radical cross coupling of hypervalent bis-catecholato silicon compounds with selenosulfonates or thiosulfonates is developed.
Org. Chem. Front., 2021,8, 1976-1982
https://doi.org/10.1039/D1QO00085C
Merging radical-polar crossover/cycloisomerization processes: access to polyfunctional furans enabled by metallaphotoredox catalysis
Metallaphotoredox catalysis for furan synthesis: The cyclisation of yne-enones proceeds smoothly via consecutive reductive radical-polar crossover and cycloisomerization processes enabled by cooperative photoredox-neutral and copper catalysis.
Org. Chem. Front., 2021,8, 1732-1738
https://doi.org/10.1039/D0QO01472A
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Hole-mediated photoredox catalysis: tris(p-substituted)biarylaminium radical cations as tunable, precomplexing and potent photooxidants
Triarylamines are demonstrated as novel, tunable electroactivated photocatalysts that use dispersion precomplexation to harness the full potential of the visible photon (>4.0 V vs. SCE) in anti-Kasha photo(electro)chemical super-oxidations of arenes.
Org. Chem. Front., 2021,8, 1132-1142
https://doi.org/10.1039/D0QO01609H
Copper-catalyzed three-component oxycyanation of alkenes
A copper-catalyzed radical oxycyanation of unactivated alkenes and styrenes to produce beta-cyanohydrin derivatives with the cyano group attached on the more substituted carbon center was reported.
Org. Chem. Front., 2021,8, 908-914
https://doi.org/10.1039/D0QO01437K
Stable dicationic dioxoliums and fate of their dioxolyl radicals
A glimpse into uncharted territory: the synthesis and study of dicationic dioxolium salts allow for assessing the fate of the corresponding elusive dioxolyl radicals.
Org. Chem. Front., 2019,6, 3184-3191
https://doi.org/10.1039/C9QO00298G
Transition metal-free, visible-light-mediated construction of α,β-diamino esters via decarboxylative radical addition at room temperature
A metal-free photoredox catalyzed decarboxylative radical coupling of free-carboxylic acids and glyoxylic oximes was developed to synthesize α,β-diamino acids.
Org. Chem. Front., 2019,6, 2245-2249
https://doi.org/10.1039/C9QO00407F
Intermolecular oxidative radical fluoroalkylfluorosulfonylation of unactivated alkenes with (fluoroalkyl)trimethylsilane, silver fluoride, sulfur dioxide and N-fluorobenzenesulfonimide
Reaction of unactivated alkenes affords various fluoroalkyl-containing alkyl sulfonyl fluorides with good functional group tolerance under mild conditions.
Org. Chem. Front., 2019,6, 447-450
https://doi.org/10.1039/C8QO01192C
Anion–π and anion–π-radical interactions in bis(triphenylphosphonium)-naphthalene diimide salts
Anion–π-radical interaction plays a key role in photophysical and magnetic properties.
Org. Chem. Front., 2019,6, 110-115
https://doi.org/10.1039/C8QO01122B
Transition-metal-free radical cleavage of a hydrazonyl N–S bond: tosyl radical-initiated cascade C(sp3)–OAr cleavage, sulfonyl rearrangement and atropisomeric cyclopropanation
Combination of 1,10-phenanthroline and potassium carbonate enables a radical cleavage of a hydrazonyl N–S bond, allowing a coupling reaction of N-tosylhydrazone and phosphinyl allene via cascade C–O cleavage, sulfonyl rearrangement and atropisomeric cyclopropanation.
Org. Chem. Front., 2018,5, 3567-3573
https://doi.org/10.1039/C8QO00873F
Visible-light-mediated allylation of alkyl radicals with allylic sulfones via a deaminative strategy
A mild and simple protocol is developed for the synthesis of terminal alkenes via site-specific C–C bond formation upon visible-light irradiation.
Org. Chem. Front., 2018,5, 3443-3446
https://doi.org/10.1039/C8QO01046C
Photoredox-catalyzed indirect acyl radical generation from thioesters
A photoredox-catalyzed method for the indirect generation of acyl radicals from stable thioesters is described.
Org. Chem. Front., 2018,5, 3267-3298
https://doi.org/10.1039/C8QO00867A
Electrochemical synthesis of 7-membered carbocycles through cascade 5-exo-trig/7-endo-trig radical cyclization
An electrochemical synthesis of functionalized 7-membered carbocycles through a 5-exo-trig/7-endo-trig radical cyclization cascade has been developed.
Org. Chem. Front., 2018,5, 3129-3132
https://doi.org/10.1039/C8QO00803E
Hydrofunctionalization of alkenols triggered by the addition of diverse radicals to unactivated alkenes and subsequent remote hydrogen atom translocation
Concomitant anti-Markovnikov hydrofunctionalization of alkenes and oxidation of remote alcohols are achieved through intramolecular 1,5(6)-hydrogen atom transfer.
Org. Chem. Front., 2018,5, 2810-2814
https://doi.org/10.1039/C8QO00734A
Metal-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process
The first example of a metal- and reductant-free deoxygenative sulfonylation of quinoline N-oxides with sodium sulfinates via a dual radical coupling process is reported.
Org. Chem. Front., 2018,5, 2604-2609
https://doi.org/10.1039/C8QO00661J
Visible-light promoted arene C–H/C–X lactonization via carboxylic radical aromatic substitution
Photocatalytic carboxylic radical aromatic substitution enables the synthesis of diversely substituted coumarins by inert C–X bond cleavage under mild conditions.
Org. Chem. Front., 2018,5, 237-241
https://doi.org/10.1039/C7QO00826K
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Selective cross-dehydrogenative C–O coupling of N-hydroxy compounds with pyrazolones. Introduction of the diacetyliminoxyl radical into the practice of organic synthesis
Oxidative C–O coupling of oximes, N-hydroxyphthalimide, and N-hydroxybenzotriazole with pyrazolones via formation of N-oxyl radicals is described.
Org. Chem. Front., 2017,4, 1947-1957
https://doi.org/10.1039/C7QO00447H
About this collection
Over the past two decades, free radical conversions have become rising stars in organic synthesis, due to their selective, specific, and mild reaction abilities. The emergence of the first radical process can be traced back to 1848, knowing as the famous Kolbe electrolysis. As reactive intermediates, free radicals participate in the cleavage and reconstruction of chemical bonds in a more controllable and efficient manner. With the advancement of science and technology, free radical reactions are being widely used in drug discovery, agricultural chemistry, material science, and other industries.
This online collection summarizes recent Organic Chemistry Frontiers articles that focus on radical-involved chemical transformations.
Articles featured in OCF focus collections are handpicked by Editors. We hope you find them enjoyable to read.