Free radicals are highly reactive towards other substances and play an important role in many chemical or biological processes. This Thematic Series presents a broad spectrum of articles extending the current knowledge in the field of organic free radicals. The range of synthetic reactions includes aerobic radical multifunctionalization of alkenes, metal-free aerobic oxidations and metal-catalyzed oxygenations, cascade radical reactions, photoinduced polymerizations and brominations. The series also includes computational studies on intermolecular reactions.
Graphical Abstract
Scheme 1: Our first- [26] and second-generation [27] approaches to (−)-agelastatin A (1).
Scheme 2: The present iron(II)-mediated aminohalogenation of N-tosyloxycarbamate 8 providing key intermediate...
Scheme 3: Aminohalogenation of azidoformate 3 (2 g scale) under FeBr2/Bu4NBr conditions.
Figure 1: Byproducts formed by aminohalogenation of N-tosyloxycarbamate 8 with FeCl2/TMSCl in EtOH (see Table 1; ent...
Scheme 4: Plausible reaction pathways in the aminohalogenation of N-tosyloxycarbamate 8 with FeX2/Bu4NX.
Scheme 5: Plausible reaction pathway to produce compounds 9 and 10.
Graphical Abstract
Scheme 1: Typical reactions for photoinitiated cationic polymerization.
Scheme 2: Examples of previously investigated architectures.
Scheme 3: Investigated Co_Pys.
Scheme 4: Other chemical compounds.
Figure 1: UV–vis absorption spectra of the investigated compounds: (A) In acetonitrile for Py_1 and acetonitr...
Figure 2: HOMO–LUMO orbitals for Py_2, Py_3, Py_5, Py_6, Py_8, Py_11 and Py_12 involved in the π–π* transitio...
Figure 3: Fluorescence quenching of 1Py_3 by the phenacylbromide (PBr) in acetonitrile/toluene (50/50). Inser...
Scheme 5: Photochemical processes for the different Co_Pys.
Figure 4: ESR spectra obtained upon irradiation of (A) Py_3/Iod, (B) Py_3/PBr and (C) Py_3/EDB in tert-butylb...
Figure 5: ESR-spin trapping spectra of Py_9/Iod in tert-butylbenzene (storage at rt for 24 h); (a) experiment...
Figure 6: Photopolymerization profiles of EPOX upon Xe–Hg lamp irradiation (λ > 340 nm) under air for differe...
Figure 7: Photopolymerization profiles of EPOX upon a Xe–Hg lamp irradiation (λ > 340 nm) under air for diffe...
Figure 8: (A) Photopolymerization profiles of EPOX-Si upon a Xe–Hg lamp irradiation (λ > 340 nm) under air fo...
Figure 9: Photopolymerization profiles of TMPTA upon Xe–Hg lamp irradiation (λ > 340 nm) in laminate for diff...
Figure 10: Photolysis of (A) the Py_3/PBr couple, (B) the Py_3/Iod couple, and (C) the Py_3/MDEA couple; Xe–Hg...
Figure 11: Photolysis of (A) the Py_11/Iod and (B) the Py_11/Iod/NVK couple. Halogen lamp irradiation. In acet...
Scheme 6: The oxidative cycle.
Scheme 7: Oxidation versus reduction cycles.
Graphical Abstract
Figure 1: O-Ethoxycarbonyl oximes prepared.
Scheme 1: Photochemical reactions of biphenyl oxime carbonates.
Figure 2: EPR spectrum during photolysis of 1f in t-BuPh at 240 K. Top (black): experimental spectrum. Bottom...
Figure 3: EPR spectrum during photolysis of 2a in t-BuPh at 230 K. Top (blue): experiment; bottom (red): simu...
Scheme 2: Ring closure of iminyl radicals derived from 2a,b.
Figure 4: DFT computed structures for 5a, 11a and their cyclisation transition states (TS). Top line: spin de...
Graphical Abstract
Scheme 1: Photoinduced radical reaction of diaryl diselenide with triphenylbismuthine.
Scheme 2: Photoinduced reaction of diphenyl disulfide with triphenylbismuthine.
Scheme 3: A plausible reaction pathway for the photoinduced reaction of diaryl diselenide with triarylbismuth...
Graphical Abstract
Figure 1: Cascade bond formation based on radical reactions.
Figure 2: Our method for controlling the geometry of substrates and the stereochemistry of cyclization.
Scheme 1: Effect of hydroxamate ester on intermolecular C–C bond-forming reactions.
Figure 3: Substrates for testing the cascade transformation.
Scheme 2: Cascade radical addition–cyclization–trapping reaction of 5 and 6A–C.
Figure 4: E/Z-selectivity of 9Aa–Ca.
Scheme 3: Enantioselective cascade reaction of 6A–C.
Figure 5: Model for the enantioselective reaction.
Scheme 4: Reaction of propiolic acid derivatives 7 and 8.
Scheme 5: Opposite regiochemical cyclization using substrate 12.
Scheme 6: Cascade reaction of 14.
Scheme 7: Enantioselective cascade reaction of 14 and 16.
Graphical Abstract
Scheme 1: Aliphatic C–H oxidation with amidines and ketimines by 1,5-H radical shift.
Scheme 2: Aliphatic C–H oxidation with hydroperoxides.
Scheme 3: Proposed reaction mechanisms for the formation of 2a, 3a, and 4a.
Scheme 4: Proposed reaction mechanisms for the formation of 5 and 6.
Scheme 5: The reaction of secondary hydroperoxide 1o.
Scheme 6: 1,4-Dioxygenation of alkanes.
Scheme 7: Aerobic 1,4-dioxygenation of alkanes in the CuCl–NHPI catalytic system.
Graphical Abstract
Scheme 1: RAFT polymerization and silica-supported RAFT polymerization of vinylbenzyl chloride (VBC).
Figure 1: Evolution of number-average molecular weight (Mn) and Mw/Mn values of the poly(VBC) chains obtained...
Figure 2: Conversion and ln([M]0/[M]) versus time for AIBN-initiated, PABTC-mediated polymerization of VBC at...
Figure 3: AIBN-initiated, PABTC-mediated polymerization of VBC with (triangles, DP 4,400) and without (circle...
Figure 4: Evolution of molecular weights of free and grafted poly(VBC) chains with conversion.
Figure 5: Plot of the average diameter and PDI of particles recovered from silica-supported RAFT polymerizati...
Figure 6: TEM micrographs of particles (A) after 2 hours and (B) after 21 hours of VBC polymerization. Scale ...
Graphical Abstract
Scheme 1: Representative C–P bond-forming reactions.
Scheme 2: General equation of homolytic substitution.
Scheme 3: Addition of diphenyl(triphenylstannyl)phosphine.
Scheme 4: Addition of diphenyl(trimethylstannyl)phosphine.
Scheme 5: Plausible mechanism of addition of R3Sn–PPh2.
Scheme 6: Addition of tetraorganodiphosphines to phenylacetylene.
Scheme 7: Plausible mechanism of anti-diphosphination.
Scheme 8: Radical diphosphination for synthesizing fluorescent material.
Scheme 9: Mechanism of thiophosphination with diphenyl(organosulfanyl)phosphine.
Scheme 10: Thiophosphination with S-thiophosphinyl O-ethyl dithiocarbonate.
Scheme 11: Photoinduced selenophosphination of allenes.
Scheme 12: Photoinduced tellurophosphination.
Scheme 13: Decarboxylative phosphorylation of carboxylic acid derivatives.
Scheme 14: Plausible mechanism of decarboxylative phosphorylation.
Scheme 15: Radical phosphination of PTOC esters with white phosphorus.
Scheme 16: Plausible mechanism of radical phosphination (Si = (Me3Si)3Si).
Scheme 17: Stereoselective phosphination leading to (S,S)-aminophosphine derivative.
Figure 1: Calculated reaction profile of homolytic substitution between Ph• and Me3Sn–PPh2 at the B2-PLYP-D/T...
Scheme 18: Phosphination with retention of axial chirality.
Scheme 19: Chemodivergent phosphination.
Scheme 20: Bis(phosphoryl)-bridged biphenyls by radical phosphination.
Scheme 21: Bis(phosphoryl)-bridged ladder triphenylene by radical phosphination.
Scheme 22: Photoinduced phosphination of perfluoroalkyl iodides with tetraphenyldiphosphine.
Scheme 23: Ti(III)-mediated radical phosphination of organic bromides with white phosphorus.
Graphical Abstract
Scheme 1: Catalytic role of NHPI in the selective oxidation of organic substrates.
Scheme 2: Radical addition of aldehydes and analogues to alkenes.
Scheme 3: NHPI/AIBN-promoted aerobic oxidation of 2,6-diisopropylnaphthalene.
Scheme 4: NHPI/AIBN-promoted aerobic oxidation of CHB.
Scheme 5: NMBHA/MeOAMVN promoted aerobic oxidation of PUFA.
Scheme 6: Alkene dioxygenation by means of N-aryl hydroxamic acid and O2.
Scheme 7: NHPI-catalyzed reaction of adamantane under NO atmosphere.
Scheme 8: Nitration of alkanes and alkyl side-chains of aromatics.
Scheme 9: Radical mechanism for the nitration of alkanes catalyzed by NHPI.
Scheme 10: Benzyl alcohols from alkylbenzenes.
Scheme 11: Catalytic cycle of laccase-NHDs mediator oxidizing system.
Figure 1: Mediators of laccase.
Scheme 12: DADCAQ/NHPI-mediated aerobic oxidation mechanism.
Scheme 13: DADCAQ/TCNHPI mediated aerobic oxidation of ethylbenzene.
Scheme 14: NHPI/xanthone/TMAC mediated aerobic oxidation of ethylbenzene.
Scheme 15: NHPI/AQ-mediated aerobic oxidation of α-isophorone.
Scheme 16: NHPI/AQ-mediated oxidation of cellulose fibers by NaClO/NaBr system.
Scheme 17: NHPI/AQ mediated aerobic oxidation of cellulose fibers.
Scheme 18: Molecule-induced homolysis by peracids.
Scheme 19: Molecule-induced homolysis of NHPI/m- chloroperbenzoic acid system.
Scheme 20: Proposed mechanism for the NHPI/CH3CHO/O2-mediated epoxidation.
Scheme 21: NHPI/CH3CHO-mediated aerobic oxidation of alkyl aromatics.
Scheme 22: Light-induced generation of PINO from N-alkoxyphthalimides.
Scheme 23: Visible-light/g-C3N4 induced metal-free oxidation of allylic substrates.
Scheme 24: NHPI/o-phenanthroline-mediated organocatalytic system.
Scheme 25: NHPI/DMG-mediated organocatalytic system.
Scheme 26: NHPI catalyzed oxidative cleavage of C=C bonds.
Scheme 27: Synthesis of hydrazine derivatives.
Graphical Abstract
Figure 1: ORTEP structure of trans-2a.
Scheme 1: Formation of bicyclic dihydrosilole 2a under high concentration conditions.
Scheme 2: Plausible reaction mechanism.
Scheme 3: Reaction 1a with Et3GeH.
Graphical Abstract
Scheme 1: A construction of spirocyclic pyrrolidinyl oxindole by tandem radical cyclization with azide [14].
Scheme 2: A tandem radical cyclization/annulation strategy for the synthesis of 4,4-spirocyclic γ-lactams wit...
Scheme 3: The synthetic methods of 1a.
Scheme 4: The tandem radical spirocyclization reaction of N-(2-(azidomethyl)allyl)-N-(2-iodophenyl)-4-methylb...
Scheme 5: Proposed mechanism for a construction of 4,4-spirocyclic indoline γ-lactam 2f by the tandem radical...
Scheme 6: Proposed mechanism for the formation of THF-incorporating product 3 from 1g.
Graphical Abstract
Scheme 1: Comparison of fragmentation reaction pathways of organic radical ions generated under the redox-rea...
Scheme 2: Using rearrangements of radicals and ions to distinguish mechanistic pathways for ET-reactions.
Figure 1: Radical anion and cation probe substances I and II, possessing 5-hexenyl structures.
Scheme 3: Reductive ET reactions of the probe I (left) and oxidative ET reactions of probe II (right).
Scheme 4: Reaction of silyl ether 1a with Cu(OAc)2 in the absence or presence of n-Bu4NF.
Scheme 5: SmI2-promoted preparation of 1 and subsequent reaction with CuX2.
Scheme 6: Reaction of cyclopropanol 1b with Cu(OAc)2.
Scheme 7: Plausible reaction pathways for the reaction of 1b with Cu(OAc)2.
Scheme 8: Reaction of cyclopropanol 1b with various copper(II) salts (CuX2).
Scheme 9: Formation of acetoamide 16 from the cation 13.
Scheme 10: Reaction of cyclopropanol 1c with various copper(II) salts (CuX2).
Scheme 11: Reaction of cyclopropanol 1d with various Cu(OAc)2.
Scheme 12: Comparison of reaction pathways of ring-expanded radical 27 and 28.
Graphical Abstract
Scheme 1: Radical addition to α-methylene-γ-phenyl-γ-butyrolactams.
Figure 1: Chelation of 5a and 5d.
Scheme 2: Synthesis of chiral substrate 10.
Scheme 3: Synthesis of chiral 4-butyl-L-pyroglutamic acid 13.
Graphical Abstract
Scheme 1: SmI2-mediated cyclisations directed by a C–Si bond.
Scheme 2: Reduction of a spirocyclic lactone using SmI2−H2O−Et3N.
Scheme 3: Stereoselective spirocyclisation of functionalised keto-lactone substrates directed by a C–Si bond.
Scheme 4: Telescoped stereoselective spirocyclisation/lactone reduction.
Scheme 5: Telescoped stereoselective spirocyclisation/lactone reduction/Peterson elimination.
Graphical Abstract
Scheme 1: Oxidative conversion of 1,3-dicarbonyl compounds to carboxylic acids with CAN.
Figure 1: Energy diagram for the unsubstituted arene with the carbonyl groups anti to each other. For TS1a’ t...
Figure 2: Possible products from the ortho cyclization of 1g and 1j.
Scheme 2: Proposed mechanism for the conversion of δ-aryl-β-dicarbonyl compounds to β-tetralones (path A) and...
Graphical Abstract
Figure 1: Structure of the SG1, TEMPO and DBN nitroxides and the BlocBuilder MA alkoxyamine.
Figure 2: Key equilibrium between active and dormant species involved in the nitroxide-mediated (NMP) polymer...
Figure 3: Degradation of the SG1 nitroxide versus time in the presence of 0 (empty stars), 1 (filled squares)...
Figure 4: Degradation of the SG1 (triangles) and TEMPO (squares) nitroxides versus time in the presence of 0 ...
Figure 5: Degradation of the SG1 nitroxide versus time in DMA (filled squares), DMF (filled triangles), MeOH ...
Figure 6: Degradation of the SG1 nitroxide versus time in the presence of 0% of lithium salt in DMA (empty sq...
Figure 7: Degradation of the TEMPO nitroxide versus time in DMA in the presence of 0% lithium salt (empty squ...
Figure 8: NMP of styrene initiated by the BlocBuilder MA alkoxyamine at 120 °C in DMA without LiCl salt. (a) ...
Scheme 1: Synthesis of the cellobiose and SG1-based alkoxyamine (cello-SG1). The shown regioisomer exhibits a...
Figure 9: (a) Evolution of the number-average molar mass (Mn: filled symbol, linear fit: dash lines) and poly...
Scheme 2: (Reversible) redox system of nitroxide.
Figure 10: Cyclic voltammograms in DMF of (a) SG1 (10−2 M)/ NaClO4 (10−1 M) and (b) LiCl (10−2 M)/TBAPF6 (10−1...
Figure 11: Cyclic voltammograms of DMF/4.5 wt % LiBr solution heated at 80 °C for 30 min (plain line) and 14 h...
Scheme 3: Hydrolysis of DMA in the presence of LiCl.
Scheme 4: Disproportionation of nitroxide 1 by acid treatment.
Figure 12: Degradation of the nitroxides (SG1 and TEMPO) in the presence of HCl. (a) TEMPO ESR signal in the p...
Graphical Abstract
Figure 1: UV–vis absorption spectra of organotellurium chain transfer agent 1 and dimethyl ditelluride in tol...
Scheme 1: Photopolymerization in the presence of organotellurium chain transfer agent 1.
Figure 2: GPC traces for the polymerizations of MMA (Table 1). The percentages in the legend refer to the ND filters...
Scheme 2: Activation and deactivation mechanism of dormant (P-TeMe) and ditelluride.
Figure 3: Experimental setup for the photopolymerization using the LED.
Graphical Abstract
Scheme 1: Experimental results for the radical arylation of epoxides.
Scheme 2: 5-exo cyclization of the hexenyl radical.
Scheme 3: Intramolecular radical additions of simple aniline derivatives.
Scheme 4: Successful catalytic radical addition to an N-methyl substituted aniline.
Figure 1: Optimized structure of the transition state of the radical addition of 1 (left: spin density plot a...
Scheme 5: Intramolecular radical additions of simple aniline derivatives.
Scheme 6: Mismatching of polar effects.
Scheme 7: Examples of p-substituted anilines investigated.
Scheme 8: Examples of m,m’-disubstituted anilines investigated.
Scheme 9: Addition reactions leading to dihydrobenzofuran and an indane.
Graphical Abstract
Scheme 1: General scheme for anodic cyclization reactions.
Scheme 2: Anodic cyclization competition study.
Scheme 3: Kolbe electrolysis reactions.
Scheme 4: Oxidative coupling between a carboxylic acid and electron-rich olefin.
Scheme 5: Predicted relative rates of single-electron oxidation based on resonance stabilization of the resul...
Figure 1: Radical cation stabilization by an o-methoxy substituent.
Graphical Abstract
Figure 1: Action spectrum of bromination with CBr4, induced by LED irradiation (red line), and absorption spe...
Scheme 1: Plausible mechanism for bromination of cyclohexane with CBr4 induced by LED irradiation.
Figure 2: 13C NMR monitoring of reaction mixtures: (a) 0.50 mmol of CBr4, 0.10 mL of cyclohexane, and 0.40 mL...
Graphical Abstract
Scheme 1: The effect of water in radical multifunctionalization reactions.
Scheme 2: Transformation of 3 into 5-amino-1,4-diol derivative 25.
Scheme 3: Proposed reaction mechanism.
Graphical Abstract
Scheme 1: Fe(acac)3-catalyzed alkenylation of cyclohexane. Catalytic conditions: cinnamic acid (1) (0.3 mmol)...
Scheme 2: Fe(acac)3-catalyzed alkenylation of cyclopentan, cycloheptane and cyclooctane. Catalytic conditions...
Scheme 3: A plausible pathway for the reaction.
Graphical Abstract
Scheme 1: Generation of NO3• (a) in the atmosphere, (b) under experimental conditions.
Figure 1: Polyester-model systems studied in this work.
Scheme 2: Products of the reaction of polyester model compounds 1–3 with NO3• in the absence of other radical...
Scheme 3: Proposed mechanism for the reaction of m-toluic acid neopentyl ester (3) with NO3• in the absence o...
Scheme 4: Products of the reaction of polyester-model compounds 1–3 with NO3• in presence of NO2•, O3, and O2....
Scheme 5: Proposed mechanism for the reaction of m-toluic acid neopentyl ester (3) with NO3• in presence of NO...
Graphical Abstract
Scheme 1: Amine radical cations’ mode of reactivity.
Scheme 2: Reductive quenching of photoexcited Ru complexes by Et3N.
Scheme 3: Photoredox aza-Henry reaction.
Scheme 4: Formation of iminium ions using BrCCl3 as stoichiometric oxidant.
Scheme 5: Oxidative functionalization of N-aryltetrahydroisoquinolines using Eosin Y.
Scheme 6: Synthetic and mechanistic studies of Eosin Y-catalyzed aza-Henry reaction.
Scheme 7: Oxidative functionalization of N-aryltetrahydroisoquinolines using RB and GO.
Scheme 8: Merging Ru-based photoredox catalysis and Lewis base catalysis for the Mannich reaction.
Scheme 9: Merging Au-based photoredox catalysis and Lewis base catalysis for the Mannich reaction.
Scheme 10: Merging Ru-based photoredox catalysis and Cu-catalyzed alkynylation reaction.
Scheme 11: Merging Ru-based photoredox catalysis and NHC catalysis.
Scheme 12: 1,3-Dipolar cycloaddition of photogenically formed azomethine ylides.
Scheme 13: Plausible mechanism for photoredox 1,3-dipolar cycloaddition.
Scheme 14: Photoredox-catalyzed cascade reaction for the synthesis of fused isoxazolidines.
Scheme 15: Plausible mechanism for the photoredox-catalyzed cascade reaction.
Scheme 16: Photoredox-catalyzed α-arylation of glycine derivatives.
Scheme 17: Photoredox-catalyzed α-arylation of amides.
Scheme 18: Intramolecular interception of iminium ions by sulfonamides.
Scheme 19: Intramolecular interception of iminium ions by alcohols and sulfonamides.
Scheme 20: Intermolecular interception of iminium ions by phosphites.
Scheme 21: Photoredox-catalyzed oxidative phosphonylation by Eosin Y.
Scheme 22: Conjugated addition of α-amino radicals to Michael acceptors.
Scheme 23: Conjugated addition of α-amino radicals to Michael acceptors assisted by a Brønsted acid.
Scheme 24: Conjugated addition of α-amino radicals derived from anilines to Michael acceptors.
Scheme 25: Oxygen switch between two pathways involving α-amino radicals.
Scheme 26: Interception of α-amino radicals by azodicarboxylates.
Scheme 27: α-Arylation of amines.
Scheme 28: Plausible mechanism for α-arylation of amines.
Scheme 29: Photoinduced C–C bond cleavage of tertiary amines.
Scheme 30: Photoredox cleavage of C–C bonds of 1,2-diamines.
Scheme 31: Proposed mechanism photoredox cleavage of C–C bonds.
Scheme 32: Intermolecular [3 + 2] annulation of cyclopropylamines with olefins.
Scheme 33: Proposed mechanism for intermolecular [3 + 2] annulation.
Scheme 34: Photoinduced clevage of N–N bonds of aromatic hydrazines and hydrazides.
Graphical Abstract
Scheme 1: Autoxidation of an organic substrate RH.
Scheme 2: Inhibition of autoxidation by radical-trapping antioxidants (e.g. ArOH).
Scheme 3: Relevant reactions in co-antioxidant systems.
Figure 1: Relevant structures 1–12.
Scheme 4: Model for kinetic solvent effects on the radical-trapping activity of phenolic antioxidants.
Figure 2: The O–H stretching region of representative FTIR spectra of compound 6b (10 mM) in CCl4 containing ...
Figure 3: Oxygen-uptake plots recorded during the AIBN initiated autoxidation of styrene in chlorobenzene (50...
Figure 4: Oxygen-uptake plots recorded during the AIBN initiated autoxidation of styrene in chlorobenzene (50...
Figure 5: Regeneration efficiencies (α) observed in autoxidations of styrene in chlorobenzene (50% v/v) at 30...