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Herein, we disclose a simple copper‐catalyzed method for enantioselective allylic C(sp3)−H oxidation of unsymmetrical acyclic alkenes, specifically 1‐aryl‐2‐alkyl alkenes. The C−H substrates are used in limiting amounts, and the products are obtained with high enantioselectivity, E/Z‐selectivity, and regioselectivity. The method exhibits broad functional group tolerance, and E/Z‐alkene mixtures are suitable C−H substrates. The transformation is enabled by light irradiation, which sustains the enantioselective copper catalysis by photoinduced oxidant homolysis. [ABSTRACT FROM AUTHOR]

The α-oxyalkylation of aryl chlorides with ethers and alcohols using a small amount of a peroxide was found to be induced by photoirradiation. The reaction proceeds through a homolytic aromatic substitution (HAS) mechanism consisting of addition of an α-oxyalkyl radical to an aryl chloride and elimination of the chlorine atom to give the α-oxyalkylation product, where photoirradiation is considered to effect not only the initiation step to facilitate homolysis of a peroxide, but also the propagating radical chain. [ABSTRACT FROM AUTHOR]

A photo-induced electron donor–acceptor (EDA) complex enabled tandem reaction of alkyne ketones via a radical difluoroalkylation/cyclization cascade sequence is reported. The EDA complex plays a key role, and the C – Br bond homolysis process may also be involved for this transformation. Varieties of difluoroalkyl-substituted thiofavones can be smoothly assembled in moderate to good yields under photocatalyst-, metal- and oxidant-free conditions, thus offering potential applications for pharmaceutical research. [ABSTRACT FROM AUTHOR]

Large or repeated mechanical loads degrade polymeric materials by accelerating chain fragmentation. This mechanochemical backbone fracture usually occurs by homolysis of otherwise inert C–C, C–O and C–S bonds, generating highly reactive macroradicals. Because backbone fracture is detrimental on its own and the resulting macroradicals can initiate damaging reaction cascades, a major thrust in contemporary polymer mechanochemistry is to suppress it, usually by mechanochemical release of "hidden length" that dissipates local molecular strain. Here we summarize an emerging complementary strategy of channelling mechanochemically generated macroradicals in reaction cascades to form new load-bearing chemical bonds, which enables local self-healing or self-strengthening, and/or to generate mechanofluorescence, which could yield detailed quantitative molecular understanding of how material-failure-inducing macroscopic mechanical loads distribute across the network. We aim to identify generalizable lessons derivable from the reported implementations of this strategy and outline the key challenges in adapting it to diverse polymeric materials and loading scenarios. [ABSTRACT FROM AUTHOR]

Decarboxylative alkylation of carboxylic acids with easily oxidizable functional groups such as phenol and indole functionalities was achieved using a catalytic amount of basic iron(III) acetate, Fe(OAc)2(OH), in the presence of benzimidazole under 427 nm LED irradiation. Kinetic analyses of this catalytic reaction revealed that the reaction rate is first‐order in alkenes and is linearly correlated with the light intensity; the faster reaction rate for the benzimidazole‐ligated species was consistent with the increased absorbance in the visible light region. Wide functional group tolerance for the easily oxidizable groups is ascribed to the weak oxidation ability of the in situ‐generated oxo‐bridged iron clusters compared with other iron(III) species. [ABSTRACT FROM AUTHOR]

Recent advances in the isolation of tamed bismuth radicals and the selective in situ generation of highly reactive bismuth radicals have set the stage for the application of these compounds in organic and organometallic synthesis and catalysis. Here, we provide a summary of the methodological approaches in the field. Important strategies for accessing bismuth radical species are presented and key examples of their applications in organic synthesis are outlined, highlighting how this class of compounds has emerged as new set of valuable tools for synthetic practitioners. 1 Introduction 2 Generation of Bismuth Radical Species by Homolysis 2.1 Temperature-Induced Homolysis 2.2 Light-Induced Homolysis 2.3 Light-/Temperature-Induced Bi–C Homolysis of Polar Oxidative Addition Complexes 3 Applications of Bismuth-Centered Radical Species in Organic Synthesis 3.1 Bismuth-Catalyzed Cycloisomerization of Iodo Olefins 3.2 Controlled Radical Polymerization Reactions 3.3 Bismuth-Promoted Pn–Pn and C–S Coupling 3.4 Bismuth-Catalyzed Dehydrocoupling of Silanes with TEMPO 3.5 Bismuth-Catalyzed C–N Coupling with Redox-Active Electrophiles 3.6 Bismuth-Catalyzed Giese-Type Coupling Reactions 3.7 Oxidative Addition of Aryl Electrophiles to Photoactive Bismuthinidenes 4 Conclusions [ABSTRACT FROM AUTHOR]

The synthesis of the organochromium(II) complexes [POCOPtBu]Cr(R) (R = p-Tol, Bn) is reported. Exposure of [POCOPtBu]Cr(Bn) to visible light promoted homolytic Cr–CBn bond cleavage and formed {[POCOPtBu]Cr}2(η1:η1μ-N2) via a putative [POCOPtBu]Cr(I) species. [ABSTRACT FROM AUTHOR]

The catalytic disproportionation of by non‐heme Fe(II) complexes of H2O2 the ligand N4Py (1,1‐bis(pyridin‐2‐yl)‐N,N‐bis(pyridin‐2‐ylmethyl)methanamine) and the formation and reactivity of Fe(III)‐OOH and Fe(IV)=O species is studied by UV/Vis absorption, NIR luminescence, (resonance) Raman and headspace Raman spectroscopy, 1O2 trapping and DFT methods. Earlier DFT studies indicated that disproportionation of H2O2 catalysed by Fe(II)‐N4Py complexes produce only 3O2, however, only the low‐spin state pathway was considered. In the present study, DFT calculations predict two pathways for the reaction between Fe(III)‐OOH and H2O2, both of which yield 3O2/H2O2 and involve either the S=1/2 or the S=3/2 spin state, with the latter being spin forbidden. The driving force for both pathways are similar, however, a minimal energy crossing point (MECP) provides a route for the formally spin forbidden reaction. The energy gap between the reaction intermediate and the MECP is lower than the barrier across the non‐adiabatic channel. The formation of 3O2 only is confirmed experimentally in the present study through 1O2 trapping and NIR luminescence spectroscopy. However, attempts to use the 1O2 probe (α ${\alpha }$ ‐terpinene) resulted in initiation of auto‐oxidation rather than formation of the expected endoperoxide, which indicated formation of OH radicals from Fe(III)‐OOH, e. g., through O−O bond homolysis together with saturation of methanol with 3O2. Microkinetic modelling of spectroscopic data using rate constants determined earlier, reveal that there is another pathway for Fe(III)‐OOH decomposition in addition to competition between the reaction of Fe(III)‐OOH with H2O2 and homolysis to form Fe(IV)=O and hydroxyl radical. Notably, after all H2O2 is consumed the decay of the Fe(III)‐OOH species is predominantly through a second order self reaction (with Fe(III)‐OOH). The conclusion reached is that the rate of O−O bond homolysis in the Fe(III)‐OOH species to form Fe(IV)=O and an hydroxyl radical is too low to be responsible for the observed oxidation of organic substrates. [ABSTRACT FROM AUTHOR]

A mononuclear, T‐shaped palladium(I) d9 metalloradical (3), stabilized by a bulky carbazole‐based PNP‐ligand, was obtained by reduction of palladium chloride or thermal Pd−C bond homolysis of the corresponding neopentyl complex. Pressurizing with CO gave the Pd(I) carbonyl complex, which was structurally characterized by X‐ray diffraction. Delocalization of the unpaired electron to the carbonyl carbon was detected by EPR spectroscopy and theoretically modeled by DFT and ab initio methods. The partially reduced and radicalized CO slowly reacts with di(tert‐butyl) disulfide under homolytic S−S cleavage and C−S bond formation to give the corresponding metallathioester. [ABSTRACT FROM AUTHOR]

A light‐driven radical oxy‐functionalization of non‐acidic aliphatic and benzylic C(sp3)−H bonds was achieved with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) in a single‐step by employing an aryl ketone as a sole catalyst. The transformation was initiated by homolysis of a C(sp3)−H bond in the starting substance by the photo‐excited aryl ketone. The derived carbon radical was then promptly trapped by TEMPO leading to the formation of the TEMPO‐adduct. The derived TEMPO‐adduct is synthetically versatile as an alcohol equivalent since it can be readily converted to the corresponding ketone by oxidation and to the corresponding alcohol by reduction. The key to realizing the present catalytic reaction relies on the distinctive triple role of TEMPO, which acts as the precursor of the oxygen functionality, the oxidant to regenerate the aryl ketone, and the protective group for the derived TEMPO‐adduct from over‐oxidation. [ABSTRACT FROM AUTHOR]

Dearomative spirocyclization reactions represent a promising means to convert arenes into three‐dimensional architectures; however, controlling the regioselectivity of radical dearomatization with nonactivated arenes to afford the spirocyclizative 1,2‐difunctionalization other than its kinetically preferred 1,4‐difunctionalization is exceptionally challenging. Here we disclose a novel strategy for dearomative 1,2‐ or 1,4‐amidoximation of (hetero)arenes enabled by direct visible‐light‐induced homolysis of N−NO bonds of nitrosamides, giving rise to various highly regioselective amidoximated spirocycles that previously have been inaccessible or required elaborate synthetic efforts. The mechanism and origins of the observed regioselectivities were investigated by control experiments and density functional theory calculations. [ABSTRACT FROM AUTHOR]

Benzo[b]phosphole oxides are valuable and significant organic functional molecules. Therefore, extensive efforts have been dedicated to the development of an environmentally friendly and convenient synthetic strategy for benzo[b]phosphole oxides. However, several critical issues still persist in the currently available protocols. In this study, we present a direct air-oxidized strategy enabling the transformation of arylphosphine oxides into phosphinoyl radicals, which were further utilized in the synthesis of benzo[b]phosphole oxides by combining with various alkynes. In addition, the results of DFT calculations show that phosphinoyl radical formation could involve an O2-mediated O–H bond homolysis instead of the commonly recognized P–H bond homolysis mechanism. [ABSTRACT FROM AUTHOR]

α‐Aminoalkylation of sulfonylarenes with alkylamines was found to be induced by photoirradiation. Here various types of alkylamines, such as trialkylamines, dialkylamines, N,N‐dialkylanilines and N‐alkylanilines as well as sulfonylarenes containing an azole, azine, heterole or benzene ring are available. The reaction proceeds through a homolytic aromatic substitution (HAS) process consisting of addition of an α‐aminoalkyl radical to a sulfonylarene and elimination of the sulfonyl radical to give the α‐arylalkylamine, where photoirradiation is considered to induce homolysis of sulfonylarenes leading to the generation of α‐aminoalkyl radicals that make a radical chain operative. [ABSTRACT FROM AUTHOR]

1,5‐X insertions of alkylidene carbenes are powerful methods to construct five‐membered carbocycles and heterocycles, but the mechanisms of these 1,5‐X insertions of alkylidene carbenes remain unclear (concerted or stepwise?). Here we disclose different mechanisms of 1,5‐X insertions of free alkylidene carbenes based on DFT calculations. Except for the 1,5 S−H insertion, all 1,5‐X insertions proceed through stepwise processes via forming ylide intermediates. However, subsequent 1,2 rearrangements of ylides occur through different mechanisms. The formal 1,5 O−H/N−H insertion except S−H insertion happens through deprotonation rather than insertion reaction, while other pathways including nucleophilic substitution, 2,3‐sigmatropic rearrangement, and homolysis of O−C bond are invoked in various 1,5 O−C insertions. The competition between 1,5‐X insertions and other side reactions (such as 1,2 migration, dealkylation) has been discussed to answer why the target insertion products were not obtained in some cases. [ABSTRACT FROM AUTHOR]

The photocatalytic coupling of ethers is uncommon because of the challenges in breaking C–O bonds and low selectivity. Herein, we report a visible light-mediated deoxygenation homocoupling of benzyl pyridyl ethers via their pyridium salts. This approach enables C(sp3)–O bond homolysis under mild conditions. Mechanistic experiments support the radical nature of the reaction. This method is highly compatible with electron-withdrawing groups and has potential applications for drug precursor synthesis. [ABSTRACT FROM AUTHOR]

Hydrophosphination activity has been solicited from the parent and decamethyl zirconocene dichloride compounds, Cp2ZrCl2 and Cp*2ZrCl2. Given recent reports of photocatalytic hydrophosphination, these compounds were irradiated in the near ultraviolet (UV) as precatalysts resulting in the successful hydrophosphination of styrene substrates and activated alkenes. Irradiation appears to induce homolysis of the Cp or Cp* ligand, resulting in radical hydrophosphination. Successful detection of this radical reactivity was achieved by monitoring for EPR signals with in situ irradiation, a methodology proving to be general for the determination of radical versus closed‐shell reactivity in transition‐metal photocatalysis. [ABSTRACT FROM AUTHOR]

The DNA photocleavage effect of halogenated O-carbamoyl derivatives of 4-MeO-benzamidoxime under UVB and UVA irradiation was studied in order to identify the nature, position, and number of halogens on the carbamoyl moiety that ensure photoactivity. F, Cl, and Br-phenyl carbamate esters (PCME) exhibited activity with the p-Cl-phenyl derivative to show excellent photocleavage against pBR322 plasmid DNA. m-Cl-PCME has diminished activity, whereas the presence of two halogen atoms reduced DNA photocleavage. The substitution on the benzamidoxime scaffold was irrelevant to the activity. The mechanism of action indicated function in the absence of oxygen, probably via radicals derived from the N-O bond homolysis of the carbamates and in air via hydroxyl radicals and partially singlet oxygen. The UVA-vis area of absorption of the nitro-benzamidoxime p-Cl-PCMEs allowed for the investigation of their potential efficacy as photopesticides under UVA irradiation against the whitefly Bemisia tabaci, a major pest of numerous crops. The m-nitro derivative exhibited a moderate specificity against the adult population. Nymphs were not affected. The compound was inactive in the dark. This result may allow for the development of lead compounds for the control of agricultural insect pests that can cause significant economic damage in crop production. [ABSTRACT FROM AUTHOR]

The addition of benzoyl peroxide to [CoII(acac)2] in a 1 : 2 ratio selectively produces [CoIII(acac)2(O2CPh)], a diamagnetic (NMR) mononuclear CoIII complex with an octahedral (X-ray diffraction) coordination geometry. It is the first reported mononuclear CoIII derivative with a chelated monocarboxylate ligand and an entirely O-based coordination sphere. The compound degrades in solution quite slowly by homolytic CoIII–O2CPh bond cleavage upon warming above 40 °C to produce benzoate radicals and can serve as a unimolecular thermal initiator for the well-controlled radical polymerisation of vinyl acetate. Addition of ligands (L = py, NEt3) induces benzoate chelate ring opening and formation of both cis and trans isomers of [CoIII(acac)2(O2CPh)(L)] for L = py under kinetic control, then converting quantitatively to the cis isomer, whereas the reaction is less selective and equilibrated for L = NEt3. The py addition strengthens the CoIII–O2CPh bond and lowers the initiator efficiency in radical polymerisation, whereas the NEt3 addition results in benzoate radical quenching by a redox process. In addition to clarifying the mechanism of the radical polymerisation redox initiation by peroxides and rationalizing the quite low efficiency factor for the previously reported [CoII(acac)2]/peroxide-initiated organometallic-mediated radical polymerisation (OMRP) of vinyl acetate, this investigation provides relevant information on the CoIII–O homolytic bond cleavage process. [ABSTRACT FROM AUTHOR]

A visible light-driven carbon–carbon bond-forming cyclization cascade under metal- and catalyst-free conditions has been reported. The cascade is initiated through a transient alkyl radical intermediate that is formed by the direct homolysis of Csp3–Br under visible light, affording a series of 3-substituted chroman-4-ones. Crucially, this work exhibited a facile and effective strategy for building three-dimensional polycyclic compounds using two-dimensional long-chain compounds as building blocks. The protocol has significant advantages such as high diastereoselectivity, high regioselectivity, metal- and catalyst-free, mild reaction conditions, controllable synthesis, and operational simplicity. [ABSTRACT FROM AUTHOR]

Heme and nonheme dimanganese catalases are widely distributed in living organisms to participate in antioxidant defenses that protect biological systems from oxidative stress. The key step in these processes is the disproportionation of H2O2 to O2 and water, which can be interpreted via two different mechanisms, namely via the formation of high-valent oxoiron(IV) and peroxodimanganese(III) or diiron(III) intermediates. In order to better understand the mechanism of this important process, we have chosen such synthetic model compounds that can be used to map the nature of the catalytically active species and the factors influencing their activities. Our previously reported μ-1,2-peroxo-diiron(III)-containing biomimics are good candidates, as both proposed reactive intermediates (FeIVO and FeIII2(μ-O2)) can be derived from them. Based on this, we have investigated and compared five heterobidentate-ligand-containing model systems including the previously reported and fully characterized [FeII(L1−4)3]2+ (L1 = 2-(2′-pyridyl)-1H-benzimidazole, L2 = 2-(2′-pyridyl)-N-methyl-benzimidazole, L3 = 2-(4-thiazolyl)-1H-benzimidazole and L4 = 2-(4′-methyl-2′-pyridyl)-1H-benzimidazole) and the novel [FeII(L5)3]2+ (L5 = 2-(1H-1,2,4-triazol-3-yl)-pyridine) precursor complexes with their spectroscopically characterized μ-1,2-peroxo-diiron(III) intermediates. Based on the reaction kinetic measurements and previous computational studies, it can be said that the disproportionation reaction of H2O2 can be interpreted through the formation of an electrophilic oxoiron(IV) intermediate that can be derived from the homolysis of the O–O bond of the forming μ-1,2-peroxo-diiron(III) complexes. We also found that the disproportionation rate of the H2O2 shows a linear correlation with the FeIII/FeII redox potential (in the range of 804 mV-1039 mV vs. SCE) of the catalysts controlled by the modification of the ligand environment. Furthermore, it is important to note that the two most active catalysts with L3 and L5 ligands have a high-spin electronic configuration. [ABSTRACT FROM AUTHOR]

The reactive HO˙/(Salophent-Bu)Co(II) radical pair was observed to be generated via homolysis of the terminal Co(III)–OH bond in transient (Salophent-Bu)(L)Co(III)(OH) (L = Py, MeOH) complexes as indicated by UV-Vis and EPR measurements. Based on this elementary process, C–H bond activations in acetone, 2-butanone, acetonitrile and benzene were achieved under ambient conditions. For the reactions of the first three substrates, the alkylcobalt(III) complexes were formed as the products. [ABSTRACT FROM AUTHOR]

Diiodomethane, CH2I2, in a polar solvent undergoes a unique photoinduced reaction whereby I2− and I3− are produced from its photodissociation, unlike for other iodine-containing haloalkanes. While previous studies proposed that homolysis, heterolysis, or solvolysis of iso-CH2I–I, which is a major intermediate of the photodissociation, can account for the formation of I2− and I3−, there has been no consensus on its mechanism and no clue for the reason why those negative ionic species are not observed in the photodissociation of other iodine-containing chemicals in the same polar solvent, for example, CHI3, C2H4I2, C2F4I2, I3−, and I2. Here, using time-resolved X-ray liquidography, we revisit the photodissociation mechanism of CH2I2 in methanol and determine the structures of all transient species and photoproducts involved in its photodissociation and reveal that I2− and I3− are formed via heterolysis of iso-CH2I–I in the photodissociation of CH2I2 in methanol. In addition, we demonstrate that the high polarity of iso-CH2I–I is responsible for the unique photochemistry of CH2I2. [ABSTRACT FROM AUTHOR]

The thermal decomposition of bis-R-substituted gem-dinitroethyl-N-nitramines in diphenyl ether solution was studied by a manometric method combined with mass spectrometry and photocolorimetry. The reaction is described by a first order equation and is not complicated by chain and heterogeneous processes. The rate-determining step of the process is the homolysis of the C—NO2 bond in the gem-dinitro group. The kinetic parameters of the rate-determining step were determined. The influence of the structure on the reactivity of the investigated compounds was analyzed. Linear relationships were found between the rate constant, the activation energy of thermal decomposition, and the steric constants of the -substituent of the reaction center. [ABSTRACT FROM AUTHOR]

Homolytic and heterolytic H 2 O 2 scissions are central to produce •OH for aqueous contaminant fragmentation. However, the kinetic, mechanistic, and energetic aspects of homolytic H 2 O 2 cleavage remain under-explored, providing impetus for research with the use of difficult-to-degrade phenol as a model pollutant. Herein, UiO-66 and its analogues functionalized with –NH 2 /-SO 3 H (UiO-66-NH 2 /UiO-66-SO 3 H) were synthesized to generate ZrO 2 poly-crystallites on N/S-doped carbon catalysts via pyrolysis (C UiO-66 /C UiO-66-NH2 /C UiO-66-SO3H). The catalyst surfaces contained distinct concentrations of Lewis basic N/S dopants, which donated electrons to adjacent Brönsted acidic –OH (BA) and Lewis acidic Zr4+ (LA) species dissimilarly, resulting in the catalysts with diverse BA/LA strengths (E BA /E LA) and areas (S BA /S LA). C UiO-66 exhibited the highest E LA and lowest E BA , which are favorable for endothermic H 2 O 2 distortion, whereas C UiO-66-SO3H exhibited the lowest E LA and highest E BA , with only E BA being favorable for endothermic •OH desorption, while leaving the other elementary steps exothermic. Kinetic analysis and DFT calculations revealed that C UiO-66-SO3H possessed the lowest energy barrier (E BARRIER), demonstrating •OH desorption was the rate-determining step alongside with the significance of high E BA for reducing E BARRIER. Meanwhile, the highest pre-factor was observed for C UiO-66 with the largest S LA , corroborating the significance of large S LA for escalating the collision frequency between Zr4+ and H 2 O 2 /•OH. These results boost to adjust E BA /S LA for promoting •OH productivity via catalytic H 2 O 2 homolysis. [Display omitted] • NH 2 /SO 3 H-modified UiO-66s are pyrolyzed to form ZrO 2 particles on N/S-doped carbons. • N/S dopants tune acidic nature of ZrO 2 , thus altering its homolytic H 2 O 2 scission dynamics. • Brönsted acidity (BA) of ZrO 2 dictates its energy barrier for homolytic H 2 O 2 scission. • Lewis acidity (LA) of ZrO 2 directs its collision frequency with H 2 O 2 /.•OH species. • ZrO 2 with high BA strength and large LA area improves homolytic H 2 O 2 scission efficiency. [ABSTRACT FROM AUTHOR]

Transition metal intermediates bearing M−X σ‐bonds are ubiquitous in metal‐mediated C−X bond transformations. Thermodynamic knowledge of M−X bond cleavage is crucial to explore relevant reactions; but little was accumulated till present due to lack of suitable determination methods. We here report the first systematic study of the Pd−X bond homolysis dissociation free energies [BDFE(Pd−X)] of representative [(tmeda)Pd(4‐F−C6H4)X] (tmeda=N,N,N′,N′‐tetramethylethylenediamine, X=OR or NHAr) in DMSO on the basis of reliable measurement of their bond heterolysis energies (ΔGhet(Pd−X)). Despite ΔGhet(Pd−O)s of palladium‐phenoxides are generally found about 8 kcal/mol smaller than ΔGhet(Pd−N)s of palladium‐amidos, their BDFE(Pd−X)s are observed comparable. The structure‐property relationship was investigated to disclose an enhancement effect of electron‐withdrawing groups on BDFE(Pd−X)s. Linear free energy relationship analysis revealed that Pd−X bonds are more sensitive than X−H bonds to structural variation. The energetic propensity of reductive elimination from arylpalladium complexes was evaluated by combinatorial use of BDFE(Pd−X)s and BDFE(C−X)s, indicating an overall thermodynamic bias to C−N bond formation. [ABSTRACT FROM AUTHOR]

Herein, we report visible light‐promoted single nickel catalysis for diverse carbon–heteroatom couplings under mild conditions. This mild, general, and robust method to couple diverse nitrogen, oxygen, and sulfur nucleophiles with aryl(heteroaryl)/alkenyl iodides/bromides exhibits a wide functional group tolerance and is applicable to late‐stage modification of pharmaceuticals and natural products. On the base of preliminary mechanistic studies, a NiI/NiIII cycle via the generation of active NiI complexes that appear from homolysis of NiII−I rather than NiII−aryl bond was tentatively proposed. [ABSTRACT FROM AUTHOR]

Enzymes that use a [4Fe‐4S]1+ cluster plus S‐adenosyl‐l‐methionine (SAM) to initiate radical reactions (radical SAM) form the largest enzyme superfamily, with over half a million members across the tree of life. This review summarizes recent work revealing the radical SAM reaction pathway, which ultimately liberates the 5′‐deoxyadenosyl (5′‐dAdo•) radical to perform extremely diverse, highly regio‐ and stereo‐specific, transformations. Most surprising was the discovery of an organometallic intermediate Ω exhibiting an Fe‐C5′‐adenosyl bond. Ω liberates 5′‐dAdo• through homolysis of the Fe–C5′ bond, in analogy to Co–C5′ bond homolysis in B12, previously viewed as biology's paradigmatic radical generator. The 5′‐dAdo• has been trapped and characterized in radical SAM enzymes via a recently discovered photoreactivity of the [4Fe‐4S]+/SAM complex, and has been confirmed as a catalytically active intermediate in enzyme catalysis. The regioselective SAM S–C bond cleavage to produce 5′‐dAdo• originates in the Jahn–Teller effect. The simplicity of SAM as a radical precursor, and the exquisite control of 5′‐dAdo• reactivity in radical SAM enzymes, may be why radical SAM enzymes pervade the tree of life, while B12 enzymes are only a few. [ABSTRACT FROM AUTHOR]

Radical coupling of thiols is an attractive route for the synthesis of disulfides, but this approach should be promoted by oxidants and/or metal salts in combination with environmentally harmful additives, which limits its substrate scope and industrial application. The ETS-10 zeolite was found to be able to catalyze the conversion of thiols to radicals with high efficiency in the absence of an oxidant or any additives for the synthesis of symmetrical disulfides. In this developed approach, the electrophilic H of the thiols interacts with the electron-rich O in the –Ti–O–Ti– unit of ETS-10, leading to the formation of a colinear SH–O bonded complex. Electron transfer occurs from O to S, resulting in the homolysis of the S–H bond to generate sulfur radicals followed by dimerization. [ABSTRACT FROM AUTHOR]

In this report, we developed a photocatalyst-free visible-light-promoted deoxygenative alkylation of imines with alcohols assisted by carbon disulfide and tricyclohexylphosphine. The key to success of this method is the activation of alcohols upon the formation and direct photoexcitation of xanthate anions. This one-pot protocol enables the selective C–O bond homolysis of diverse primary, secondary and tertiary alcohols to react with a variety of N-sulfonyl and N-aryl imines, providing a general and efficient platform for α-branched amine synthesis from alcohols. [ABSTRACT FROM AUTHOR]

Amide bonds connect the amino acids in proteins and exist as a prevalent structural motif in biomolecules. Herein, we have exploited the concept of cross‐electrophile coupling by merging the photo‐redox and transition‐metal catalysis to construct carbamides from superabundant (hetero)aryl halides along with commercially feasible carbamoyl chlorides. The success of this method relies on the prior formation of NiII‐aryl halide intermediates, which involves in a photoexcited Ni‐halide homolysis event by energy transfer from aryl bromide and single‐electron transfer from aryl chloride to assist generation of the vital carbamoyl radical. The breadth of application of this technique is demonstrated both in inter‐ as well as intramolecular routes for the synthesis of a plethora of (hetero)aryl carbamides with diverse functionalities, and biologically important benzolactams. [ABSTRACT FROM AUTHOR]

A computational study of the pyrolysis of 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives is carried out employing density functional theory (DFT) and high‐level coupled‐cluster methods, such as coupled‐cluster singles and doubles with perturbative triples [DLPNO‐CCSD(T)]. Our results demonstrate that the reaction proceeds through the products formed by the electrocyclization, as opposed to the mechanism suggested by Mcnab (J. Chem. Soc. Chem. Commun. 1980, 422–423), in which the reaction proceeds by starting via formation of the iminyl radicals. Our results demonstrate that the products formed by electrocyclization are responsible for the formation of iminyl radicals, contrary to homolysis of N−N bond of 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives proposed by Mcnab. Besides, our results showing that the reaction starts with the electrocyclization very well clarify why the formation of ortho‐cyclization product, contrary to ipso‐cyclization from 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives as the main product. Therefore, our results are in agreement with the experimental results for pyrolysis of 1,5‐diaryl‐1,2,5‐triazapentadiene derivatives. [ABSTRACT FROM AUTHOR]

Saddle‐shaped hemes have been discovered in the structures of most peroxidases. How such a macrocycle deformation affects the reaction of FeIII hemes with hydrogen peroxide (H2O2) to form high‐valent Fe‐oxo species remains uncertain. Through examination of the ESI‐MS spectra, absorption changes and 1H NMR chemical shifts, we investigated the reactions of two FeIII porphyrins with different degrees of saddling deformation, namely FeIII(OETPP)ClO4 (1OE) and FeIII(OMTPP)ClO4 (1OM), with tert‐butyl hydroperoxide (tBuOOH) in CH2Cl2 at −40 °C, which quickly resulted in O−O bond homolysis from a highly unstable FeIII‐alkylperoxo intermediate, FeIII‐O(H)OR (2) into FeIV‐oxo porphyrins (3). Insight into the reaction mechanism was obtained from [tBuOOH]‐dependent kinetics. At −40 °C, the reaction of 1OE with tBuOOH exhibited an equilibrium constant (Ka=362.3 M−1) and rate constant (k=1.87×10−2 sM−>1) for the homolytic cleavage of the 2 O−O bond that were 2.1 and 1.4 times higher, respectively, than those exhibited by 1OM (Ka=171.8 M−1 and k=1.36×10−2 s−1). DFT calculations indicated that an FeIII porphyrin with greater saddling deformation can achieve a higher HOMO ([Fe(dz2 ,dx2-y2)‐porphyrin(a2u)]) to strengthen the orbital interaction with the LUMO (O−O bond σ*) to facilitate O−O cleavage. [ABSTRACT FROM AUTHOR]

We report herein a modular catalytic method for the efficient enantioselective synthesis of chiral allylboronates from abundant feedstock chemicals through an asymmetric 1,1‐difunctionalization of alkenes. This protocol is distinguished by its use of an inexpensive chiral catalyst, mild and convenient reaction conditions, wide substrate scope, scalability and practicality. The utility of this method is demonstrated by the rapid synthesis of key intermediates of complex drug molecules. Mechanistic studies reveal that β‐H elimination is a highly regioselective step and the reversible homolysis and convergance to the lower energy pre‐reductive elimination intermediate is the enantio‐determining step. [ABSTRACT FROM AUTHOR]

Catalysis by radical enzymes dependent on coenzyme B12 (AdoCbl) relies on the reactive primary 5′‐deoxy‐5′adenosyl radical, which originates from reversible Co−C bond homolysis of AdoCbl. This bond homolysis is accelerated roughly 1012‐fold upon binding the enzyme substrate. The structural basis for this activation is still strikingly enigmatic. As revealed here, a displaced firm adenosine binding cavity in substrate‐loaded glutamate mutase (GM) causes a structural misfit for intact AdoCbl that is relieved by the homolytic Co−C bond cleavage. Strategically interacting adjacent adenosine‐ and substrate‐binding protein cavities provide a tight caged radical reaction space, controlling the entire radical path. The GM active site is perfectly structured for promoting radical catalysis, including "negative catalysis", a paradigm for AdoCbl‐dependent mutases. [ABSTRACT FROM AUTHOR]

Herein, we report a polar‐radical relay strategy for α‐C−H amination of cyclic amines with N‐chloro‐N‐sodio‐carbamates. The relay is initiated by in situ generation of cyclic iminium intermediate using N‐iodosuccinimide (NIS) oxidant as an initiator, which then operates through a series of polar (addition and elimination) and radical (homolysis, hydrogen‐ and halogen atom transfer) reactions to enable the challenging C−N bond formation in a controlled manner. A broad range of α‐amino cyclic amines were readily accessed with excellent regioselectivity, and the superb applicability was further demonstrated by functionalization of biologically relevant compounds. [ABSTRACT FROM AUTHOR]

The formation of C(sp3)-centered radicals via the electro--induced homolysis of 4-alkyl-1,4-dihydropyridines (alkyl-DHPs) is reported. The resulting alkyl radicals reacted with 4-hydroxyquinazolines or quinones to afford 2-alkyldihydroquinazolinones or alkylated quinones. A broad range of alkyl DHPs could be used as versatile radical precursors under electrolysis conditions. This alterative strategy provided a simple and effective pathway for the construction of C(sp2)–C(sp3) and C(sp3)–C(sp3) bonds under mild conditions. [ABSTRACT FROM AUTHOR]

5-Iodouracil (5-IU) can be integrated into DNA and acts as a UV sensitive chromophore suitable for probing DNA structure and DNA-protein interactions based on the photochemical reactions of 5-IU. Here, we perform joint studies of time-resolved Fourier transform infrared (TR-FTIR) spectroscopy and ab initio calculations to examine the state-specific photochemical reaction mechanisms of the 5-IU. The fact that uracil (U) is observed in TR-FTIR spectra after 266 nm irradiation of 5-IU in acetonitrile and ascribed to the product of hydrogen abstraction by the uracil-5-yl radical (U.) provides experimental evidence for the C--I bond homolysis of 5-IU. The excited state potential energy curves are calculated with the complete active space second-order perturbation//complete active space selfconsistent field method, from which a singlet predissociation mechanism is elucidated. It is shown that the initially populated 1(ππ*) state crosses with the repulsive 1(πσ*) or 1(nIσ*) state, through which 5-IU undergoes dissociation to the fragments of (U.) radical and iodine atom. In addition, the possibility of intersystem crossing (ISC) is evaluated based on the calculated vertical excitation energies. Although a probable ISC from 1(ππ*) state to 3(nOπ*) and then to the lowest triplet 3(ππ*) could occur in principal, there is little possibility for the excited state populations bifurcating to triplet manifold, given that the singlet state predissociation follows repulsive potential and should occur within dozens to hundreds of femtoseconds. Such low population of triplet states means that the contribution of triplet state to photoreactions of 5-IU should be quite minor. These results demonstrate clearly a physical picture of C--I bond homolysis of 5-IU and provide mechanistic illuminations to the interesting applications of 5-IU as photoprobes and in radiotherapy of cancer. [ABSTRACT FROM AUTHOR]

A facile, efficient and green synthetic method for the preparation of unsymmetric S-(2-amlnophenyl) arenethlosulfonates and 2-arylbenzothiazoles through a tandem reaction of 2,2'-diaminodiphenyldisulfides, sulfinic acids and aromatic aldehydes was developed. Mechanistic studies demonstrate that the NH2 group in disulfides has a positive influence on the tandem reaction, and simultaneous cyclization and coupling transformations can be completed after the homolysis of disulfides. This tandem reaction shows a broad substrate scope and a good functional group tolerance. A large number of products have been prepared in good to excellent yields under metal- and catalyst-free conditions with good atom economy. [ABSTRACT FROM AUTHOR]

The photochemistry of aryl chlorides having a X-SiMe3 group (X = O, NR, S, SiMe2) tethered to the aromatic ring has been investigated in detail, with the aim to generate valuable ϭ,π-heterodiradicals. Two competitive pathways arising from the excited triplet state of the aromatics have been observed, namely heterolysis of the aryl–chlorine bond and homolysis of the X–silicon bond. The former path is found in chlorinated phenols and anilines, whereas the latter is exclusive in the case of silylated thiophenols and aryl silanes. A combined experimental/computational approach was pursued to explain such a photochemical behavior. Graphical abstract [ABSTRACT FROM AUTHOR]

Showcasing the concept of light-induced homolysis for the generation of radicals, the CuII-photocatalyzed decarboxylative oxygenation of carboxylic acids with molecular oxygen as the terminal oxidant is described. Two CuII-carboxylate complexes with different coordination geometries were synthesized and characterized by X-ray analysis, correlating their structure with their ability to initiate light-induced decarboxylations. [ABSTRACT FROM AUTHOR]

The unimolecular decomposition pathways of n‐butyl nitroxyethylnitramine (BuNENA) were computationally investigated. The O−NO2 bond dissociation energies (BDEs) are found to be smaller than the N−NO2 BDEs. The consecutive NO2 elimination via TSA1 is more favorable kinetically than that via TSA2 although both of them form the same intermediate of n‐butyl‐aminoacetaldehyde (BuAAA). Isomerization of n‐butyl‐nitramineethyloxidanyl radical (BuNEȮ) formed by homolytic cleavage of O−NO2 bond was found to eliminate NO2 with a negative bond dissociation energy. Among the NO2 elimination pathways, the formation of C4H9NCH2 (PB2b), CH2O, and NO2 from BuNEȮ via the saddle point TSB2a was found to be the most kinetically favorable with a low activation energy barrier. In contrast, the consecutive HONO elimination is the most thermodynamically favorable with a high exothermicity (−▵H0). The first‐principle kinetic Monte Carlo (kMC) simulations show that the NO2 elimination of BuNEȮ via TSB2a plays an important role in driving the decomposition of BuNENA. [ABSTRACT FROM AUTHOR]

A Zn2+-induced reactive separation method for the purification of β-bromoethylbenzene from α-β-bromoethylbenzene mixtures is discovered, where the selective decomposition of α-bromoethylbenzene follows a radical mechanism. Zn2+ facilitates the homolysis of the C–Br bond of halohydrocarbons with benzyl bromide, enabling the separation of the corresponding isomers with almost identical physical properties. [ABSTRACT FROM AUTHOR]

Advanced oxidation technologies often use peroxymonosulfate in the presence of CoIIaq. It is commonly assumed that the reaction of Co(H2O)62+ with HSO5− yields CoIIIaq and SO4.−. DFT results point out that first CoII(SO5)(H2O)2 is formed. The homolysis of CoII(SO5)(H2O)2 to yield (H2O)CoII(SO5)OH.+SO4.−, is exothermic but has a large activation energy. However the cobalt is not oxidized in this reaction. CoII(SO5)(H2O)2 reacts with a second HSO5− to form CoII(SO5)2(H2O)2− that decomposes via disproportionation of the monoperoxysulfate ions without oxidation of the central cobalt ion. Surprisingly even in the presence of ligands, L, that stabilize CoIII, i. e., pyrophosphate; tri‐polyphosphate and ATP, the experimentally observed reaction mechanism involves the formation of LCoII‐OOSO3aq which then reacts with another HSO5− to form LCoII‐(OOSO32−)2. The latter complex decomposes via disproportionation of the monoperoxysulfate ligands followed by oxidation of the central cobalt cation. Alternatively, in the presence of excess CoIILaq, LCoII‐OOSO3aq reacts with CoIILaq to form 2CoIIILaq. These results point out that the mechanism of advanced oxidation processes initiated by a mixture of Co(H2O)62+ and HSO5− must be re‐considered. [ABSTRACT FROM AUTHOR]

(E)-β-Iodo vinylsulfones are synthesized under ultrasound irradiation using alkynes, sulfonyl hydrazides, potassium iodide and hydrogen peroxide. The key features of this protocol are the speed and efficiency of the reactions, which afford good to excellent yields of the desired products by employing ultrasound as the driving force. Mechanistic studies reveal that a sulfonyl radical intermediate is generated via sulfonyl iodide homolysis. [ABSTRACT FROM AUTHOR]

Bimolecular homolytic substitution (SH2) is an open-shell mechanism that is implicated across a host of biochemical alkylation pathways. Surprisingly, however, this radical substitution manifold has not been generally deployed as a design element in synthetic C–C bond formation. We found that the SH2 mechanism can be leveraged to enable a biomimetic sp3-sp3 cross-coupling platform that furnishes quaternary sp3-carbon centers, a long-standing challenge in organic molecule construction. This heteroselective radical-radical coupling uses the capacity of iron porphyrin to readily distinguish between the SH2 bond-forming roles of open-shell primary and tertiary carbons, combined with photocatalysis to generate both radical classes simultaneously from widely abundant functional groups. Mechanistic studies confirm the intermediacy of a primary alkyl–Fe(III) species prior to coupling and provide evidence for the SH2 displacement pathway in the critical quaternary sp3-carbon bond formation step. [ABSTRACT FROM AUTHOR]

Dynamic hazard and coal spontaneous combustion are major potential safety hazards in coal mines with enriched gas and spontaneously inflammable property. However, the initial oxidizability of coal samples after dynamic hazard has yet to be understood. A simplified device for dynamic hazard simulation of coal-and-gas outburst was established. The physical and chemical changes of coal surface, and their effects on initial oxidation were analyzed. Firstly, loose coal was pressurized by gas step-by-step, and the CO content was enhanced with increase in gas pressure. Meanwhile, the specific surface area provides a hotbed for low-temperature oxidation of radicals and functional groups of coal. Finally, the mechanism of mechanical force on the increase of radical and active groups with the homolysis of covalent bond was discussed. The initial oxidizability of coal after dynamic damage was characterized by oxygen absorption. The physicochemical characteristics suitable for coal oxidation, were formed under the mechano–chemical effect. The findings presented in here add to our understanding of the influence of dynamic hazard on coal oxidation. [ABSTRACT FROM AUTHOR]

This article, titled "Editorial: Photocatalytic functionalization of inert or unsaturated bonds," discusses the advancements in the field of photoredox catalysis and its application in the functionalization of inert or unsaturated bonds. The article highlights the diverse transformations and catalytic scenarios made possible by photocatalysis, which offers a green and intuitive strategy for constructing valuable molecules. The research topic focuses on recent achievements in visible-light-induced transformations of inert, double, or triple bonds, including the functionalization of sp2 and sp3 C-H bonds, difunctionalization of C=C bonds, and the photophysical properties of unsaturated compounds. The article also mentions several reviews that have provided summaries on the utilization of photoredox catalysis in C-H bond functionalization. Overall, this research topic presents fruitful synthetic methodologies and mechanism research achievements in the field of functionalization of inert or unsaturated bonds via photoredox catalysis. [Extracted from the article]

We describe herein that the cross‐coupling of bromodifluoroacetamides with (iodoethynyl)arenes proceeds without recourse to any photocatalyst when exposed to visible light at room temperature to afford alkynyldifluoroacetamides in 62–83% yields (27 examples). Several control experiments suggest that the reaction involves the homolysis of bromodifluoroacetamides and the coupling of the resultant difluoromethyl radical species with the 1‐iodoalkynes via a radical chain process. Divergent transformations of the coupling products led to various organofluorine compounds, demonstrating the synthetic utility of the developed photo‐coupling method. [ABSTRACT FROM AUTHOR]

A hetero-tetranuclear CeNi3 complex with a macrocyclic ligand catalysed the aerobic oxygenation of a methylene group adjacent to a carbonyl group under visible-light radiation to produce the corresponding α-diketones. The visible-light induced homolysis of the Ce–O bond of a bis(enolate) intermediate is proposed prior to aerobic oxygenation. [ABSTRACT FROM AUTHOR]