Search

Vibrational relaxation of HOD(v12, v3) molecules by collisions with Ar was studied at 298 K (v12 denotes coupled bending, v2, and OD stretching, v1, vibrational modes and v3 denotes OH stretching mode). The vibrationally excited HOD molecules were generated by exothermic abstraction reactions of OD radicals with 13 different RH reactants and observed by infrared emission from a fast-flow reactor as a function of Ar pressure and reaction time. State-specific relaxation rate constants were obtained by comparison of the time evolution of the experimental vibrational distributions with numerical kinetic calculations for vibrational populations. The relaxation mechanism was based on the relaxation scheme of H2O studied earlier with the addition of specific channels for HOD(v12, v3). Unlike H2O, energy in stretching and bending vibrations of HOD cannot be separated due to close ν1 and 2ν2 energies, which leads to fast collisional equilibration between these Fermi-resonant levels. For relaxation of the only pure bending state (10), a rate constant of (1.5 ± 0.3) × 10−13 cm3 molecule−1 s−1 was obtained. The relaxation rate of higher v12 states linearly increases with quantum number and very likely includes transfer of population from OD stretch levels, v1, to a lower energy bend level. The average rate constants for the loss of population from (01), (02), and (03) stretching states are (1.1 ± 0.3) × 10−14, (3.2 ± 1.0) × 10−14, and (5.6 ± 1.2) × 10−14 cm3 molecule−1 s−1, respectively. [ABSTRACT FROM AUTHOR]

The gas-phase reaction Cl + NH3 → HCl + NH2 is a prototypical hydrogen abstraction reaction, whose minimum energy path involves several intermediate complexes. In this work, a full-dimensional, spin–orbit corrected potential energy surface (SOC PES) is constructed for the ground electronic state of the Cl + NH3 reaction. About 52 000 energy points are sampled and calculated at the UCCSD(T)-F12a/aug-cc-pVTZ level, in which the data points located in the entrance channel are spin–orbit corrected. The spin–orbit corrections are predicted by a fitted three-dimensional energy surface from about 7520 energy points in the entrance channel at the level of CASSCF (15e, 11o)/aug-cc-pVTZ. The fundamental-invariant neural network method is utilized to fit the SOC PES, resulting in a total root mean square error of 0.12 kcal mol−1. The calculated thermal rate constants of the Cl + NH3 → HCl + NH2 reaction on the SOC PES with the soft-zero-point energy constraint agree reasonably well with the available experimental values. [ABSTRACT FROM AUTHOR]

Reliable thermodynamic and kinetic properties of free radical polymerization reactions are essential for synthesizing both primary polymeric materials and specialty polymers. The computational generation of these data from quantum chemistry requires a time-efficient method capable of capturing the essential physics. One such method, fixed-node diffusion Monte Carlo (FN-DMC) (using single Slater–Jastrow trial wavefunctions), has demonstrated the capability to recover 90%–95% of missing dynamic correlation energy for typical systems. In this study, methyl radical addition to ethylene serves as a simple model to test FN-DMC's ability to calculate enthalpies of reaction and activation energies with different time steps, antisymmetric trial wavefunctions, basis set sizes, and effective core potentials. The FN-DMC computational protocol thus defined for methyl radical addition to ethylene is subsequently benchmarked against Weizmann-1 and experimental reaction enthalpies from Lin et al.'s test set of 21 radical addition and 28 hydrogen abstraction enthalpies. Our findings reveal that FN-DMC consistently generates reaction enthalpies with chemical accuracy, exhibiting mean absolute deviation of 3.5(7) and 1.4(8) kJ/mol from the Weizmann-1 reference for radical addition and hydrogen abstraction reactions, respectively. Given its favorable computational scaling and high degree of parallelizability, we, therefore, recommend more comprehensive testing of FN-DMC with effective core potentials to address more extensive and intricate polymerization reactions and reactions with other radicals. [ABSTRACT FROM AUTHOR]

Resonant electron capture by aza and diaza derivatives of phenanthrene (7,8-benzoquinoline and 1,10-phenanthroline) and anthracene (acridine and phenazine) at incident free electron energies (Ee) in the range of 0–15 eV was studied. All compounds except 7,8-benzoquinoline form long-lived molecular ions (M−) at thermal electron energies (Ee ∼ 0 eV). Acridine and phenazine also form such ions at epithermal electron energies up to Ee = 1.5–2.5 eV. The lifetimes (τa) of M− with respect to electron autodetachment are proportional to the extent of aza-substitution and increase on going from molecules with bent geometry of the fused rings (azaphenanthrenes) to linear isomers (azaanthracenes). These regularities are due to an increase in the adiabatic electron affinities (EAa) of the molecules. The EAa values of the molecules under study were comprehensively assessed based on a comparative analysis of the measured τa values using the Rice–Ramsperger–Kassel–Marcus theory, the electronic structure analysis using the molecular orbital approach, as well as the density functional calculations of the total energy differences between the molecules and anions. The only fragmentation channel of M− ions from the compounds studied is abstraction of hydrogen atoms. When studying [M–H]− ions, electron autodetachment processes were observed, the τa values were measured, and the appearance energies were determined. A comparative analysis of the gas-phase acidity of the molecules and the EAa values of the [M–H]· radicals revealed their proportionality to the EAa values of the parent molecules. [ABSTRACT FROM AUTHOR]

Polariton chemistry may provide a new means to control molecular reactivity, permitting remote, reversible modification of reaction energetics, kinetics, and product yields. A considerable body of experimental and theoretical work has already demonstrated that strong coupling between a molecular vibrational mode and the confined electromagnetic field of an optical cavity can alter chemical reactivity without external illumination. However, the mechanisms underlying cavity-altered chemistry remain unclear in large part because the experimental systems examined previously are too complex for detailed analysis of their reaction dynamics. Here, we experimentally investigate photolysis-induced reactions of cyanide radicals with strongly-coupled chloroform (CHCl3) solvent molecules and examine the intracavity rates of photofragment recombination, solvent complexation, and hydrogen abstraction. We use a microfluidic optical cavity fitted with dichroic mirrors to facilitate vibrational strong coupling (VSC) of the C–H stretching mode of CHCl3 while simultaneously permitting optical access at visible wavelengths. Ultrafast transient absorption experiments performed with cavities tuned on- and off-resonance reveal that VSC of the CHCl3 C–H stretching transition does not significantly modify any measured rate constants, including those associated with the hydrogen abstraction reaction. This work represents, to the best of our knowledge, the first experimental study of an elementary bimolecular reaction under VSC. We discuss how the conspicuous absence of cavity-altered effects in this system may provide insights into the mechanisms of modified ground state reactivity under VSC and help bridge the divide between experimental results and theoretical predictions in vibrational polariton chemistry. [ABSTRACT FROM AUTHOR]

The hydrogen abstraction reaction of the cyano radical with molecules of ethane presents some interesting points in the chemistry from ultra-cold to combustion environments especially with regard to HCN(v) product vibrational distribution. In order to understand its dynamics, a new analytical full-dimensional potential energy surface was developed, named PES-2023. It uses a combination of valence bond and mechanic molecular terms as the functional form, fitted to high-level ab initio calculations at the explicitly correlated CCSD(T)-F12/aug-cc-pVTZ level on a reduced and selected number of points describing the reactive process. The new surface showed a continuous and smooth behavior, describing reasonably the topology of the reaction: high exothermicity, low barrier, and presence of intermediate complexes in the entrance and exit channels. Using quasi-classical trajectory calculations (QCT) on the new PES-2023, a dynamics study was performed at room temperature with special emphasis on the HCN(v1,v2,v3) product stretching and bending vibrational excitations, and the results were compared with the experimental evidence, which presented discrepancies in the bending excitation. The available energy was mostly deposited as HCN(v) vibrational energy with the vibrational population inverted in the CH stretching mode and not inverted in the CN stretching and bending modes, thus simulating the experimental evidence. Other dynamics properties at room temperature were also analyzed; cold rotational energy distribution was found, associated with a linear and soft transition state, and backward scattering distribution was found, associated with a rebound mechanism. [ABSTRACT FROM AUTHOR]

This study explores the potential of using electrochemical (EC) methods for valorizing lignin, a lignocellulosic biomass cell wall component, into biofuels and high-value compounds. Traditional direct electroreduction as well as oxidation of lignin have faced challenges in efficiency and selectivity due to the requirement of high oxidation potentials and expensive, toxic electrodes, leading to uncontrolled degradation. We propose using a hydrogen atom transfer (HAT) mediator to achieve benzylic oxidation, enhancing efficiency and selectivity under milder conditions. The research employs the NREL model for producing ethanol to evaluate the commercial viability of EC lignin conversion. We carried out a techno-economic analysis (TEA) and a life cycle assessment (LCA) using BioSTEAM and GREET® 2022, respectively, to evaluate the process's economic and environmental impacts over 20 years. Sensitivity analysis has been conducted to examine base case values extracted from the catalytic performance of phthalimide-N-oxyl type HAT mediators. Our findings suggest that a 2000 metric tonnes per day biorefinery using this method could produce approximately 49.56 tpd of chemicals, with the EC unit consuming 3.5% of the input energy. The TEA operating cost for chemical production was estimated at $16.86 per kg, with a total capital expenditure of $403 769 MM. The LCA revealed that producing by-products in ethanol production can lead to around 10 to 46% reduction in total CO2 emissions, depending on the employed allocation methods. The study indicates that integrating an EC unit using a HAT mediator into second-generation biorefineries for lignin oxidation followed by a reduction in chemicals could offer additional revenue streams and lower environmental impacts compared to conventional methods. [ABSTRACT FROM AUTHOR]

The aminocarbonylation of alkenes is an efficient approach to synthesize important β-amino acid motifs. However, simple and convenient methods are still rare. Herein, we present a novel visible-light-mediated controllable three-component radical relay coupling of alkenes, alkyl formates and oxime esters. By the combination of hydrogen atom transfer and energy transfer processes, a series of β-amino esters could be obtained smoothly in one step under mild conditions. We expect that the approach can complement current methodologies for the synthesis of β-amino esters. [ABSTRACT FROM AUTHOR]

Nickel catalysis is a well-established and powerful tool for C–C cross-coupling reactions, and its versatility has expanded significantly over past decades by its combination with visible-light photocatalysis in metallaphotoredox chemistry. Photocatalysis enables the activation of traditionally inert substrates and turnover of the Ni catalyst through a single-electron transfer processes. In recent years, dual catalysis has been further empowered by photoactive Ni intermediates, which exhibit distinct reactivity profiles from their ground states and complement existing protocols. This short review focuses on the emergent subclass of metallaphotoredox catalysis in which the synergy of a photoactive Ni catalyst and a typical photocatalyst (e.g., a polypyridyl Ir complex) provide solutions to challenging C–C bond formation. 1 Introduction 2 Photoactive Nickel Complexes 3 HAT-Mediated C–C Cross-Coupling 4 Halofunctionalization of π-Systems 5 Photoelimination of an Aryl Radical 6 Conclusion [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A greener and more convenient alternative to traditional methods for the generation of thiyl radical as hydrogen atom transfer (HAT) catalyst is developed, using molecular oxygen to oxidize thiol without the need for chemical initiators or light irradiation. The thiol/oxygen catalysis enables selective and efficient difunctionalization of borane. [ABSTRACT FROM AUTHOR]

Efficient transition‐metal‐free synthesis of benzo[b]azepines and oxindoles is achieved via a radical relay cascade strategy employing halogen atom transfer (XAT) for aryl radical generation followed by intramolecular hydrogen atom transfer (HAT). Optimization yielded moderate to substantial yields under visible light irradiation. Preliminary biological assessments revealed promising anti‐tumor activity for select compounds. This study underscores the potential of XAT‐mediated radical relay cascades in medicinal chemistry and anticancer drug discovery. [ABSTRACT FROM AUTHOR]

The efficient "on water" protocol was developed by employing molybdenum‐based polyoxometalate [N(C4H9)4]2[Mo6O19] as the photocatalyst. This water‐accelerated photoinduced process affords versatile ketones from aldehydes straightforwardly, showcasing exceptional substrate generality. Its applicability to life‐related molecules such as amino acids, peptides, and sugars, further demonstrates its potential for bioorthogonal application. The mechanistic investigation highlights the hydrogen atom transfer (HAT) process between the excited‐state POM and benzaldehyde for acyl radical formation. This highly reactive acyl radical is readily trapped by the Michael acceptor, thereby enabling subsequent C−H functionalization. Highly efficient gram‐scale flow operation underlines the industrial applicability of this transformative strategy. [ABSTRACT FROM AUTHOR]

A cobalt‐catalyzed intramolecular Markovnikov hydroalkoxycarbonylation and hydroaminocarbonylation of unactivated alkenes has been developed, enabling highly chemo‐ and regioselective synthesis of α‐alkylated γ‐lactones and α‐alkylated γ‐lactams in good yields. The mild reaction conditions allow use of mono‐, di‐ and trisubstituted alkenes bearing a variety of functional groups. Preliminary mechanistic studies suggest the reaction proceeds through a CO‐mediated hydrogen atom transfer (HAT) and radical‐polar crossover (RPC) process, in which a cationic acylcobalt(IV) complex is proposed as the key intermediate. [ABSTRACT FROM AUTHOR]

Non‐activated linear α‐olefins are valuable building blocks for organic transformation or olefin (co)polymerization, but they are recognized as textbook knowledge for non‐homopolymerizable monomers under radical conditions. In this article, we disclose our effort to achieve an unprecedented library of all carbon‐bonded sequence‐regulated polymers via radical isomerization homopolymerization of α‐olefin derivatives. The success of this distinctive polymerization is attributed to the remarkable efficiency and selectivity exhibited during the cyano group migration or hydrogen atom transfer, which is greatly enhanced by the precise engineering of their monomer structures. This polymerization process enables the elongation of polymer chains by five, six, or seven carbon atoms at each propagation step. These polymers, obtained through the cyano group migration or hydrogen atom transfer involved radical isomerization polymerization processes, emerge as promising candidates resembling polyethylene or polyacrylonitrile copolymers. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A greener and more convenient alternative to traditional methods for the generation of thiyl radical as hydrogen atom transfer (HAT) catalyst is developed, using molecular oxygen to oxidize thiol without the need for chemical initiators or light irradiation. The thiol/oxygen catalysis enables selective and efficient difunctionalization of borane. [ABSTRACT FROM AUTHOR]

Azoles are widely used as bioactive substances, herbicides, catalysts, corrosion inhibitors, polymeric compositors, organometallic ligands, and optical elements' components. The interaction with water plays a crucial role in many applications of azoles. The objective of this study is to observe the molecular interaction and structural transformations of 1,2‐ and 1,3‐diazoles', 1,2,3‐ and 1,2,4‐triazoles' complexes with water molecules. We have selected the most valuable for application and theoretical interest azoles with different molecular structures, which have allowed us to consider the basic features of their aqueous complexes. We used the IR study method allowing to fix water intermediates in the solid phase. We have also employed the hybrid B3LYP functional DFT method with GD3BJ dispersion correction. At the cluster formation, the hydrogen atom transfer arises, providing a labile spatial arrangement of the water system. The formation of azoles' complexes with a hydronium ion having relatively low binding energy allows the reshaping of the complexes' structure at the hydrogen atom cluster‐to‐cluster transition. The complex formation is accompanied by the hydrogen atom transfer with the participation of both water and azole hydrogen atoms. This transfer provides the mobile spatial arrangement of clusters and hydrogen atom transition from donor to acceptor centers. [ABSTRACT FROM AUTHOR]

To extend the rule‐based approach for hydrogen abstraction reactions from oxygenated compounds, a systematic investigation was performed to examine the reactivity of gas‐phase hydrogen abstraction reactions from alkyl groups (methyl and ethyl groups) bound to oxygen atoms in five types of oxygenated compounds (alcohols, ethers, formate esters, acetate esters, and carbonate esters) by H atoms and HO2 radicals comprehensively considering rotational conformers. Quantum chemical calculations were conducted at the CBS‐QB3 level for stationary points. Rate constants were determined employing conventional transition state theory (TST). For hydrogen abstraction reactions by H, the rotational conformer distribution partition function was employed to approximate partition functions, owing to the similarity in vibrational energy‐level structures among conformers. In hydrogen abstraction reactions by HO2, the vibrational structures of transition‐state (TS) conformers varied significantly due to the hydrogen bonding, leading to an inappropriate evaluation of rate constants when using the lowest‐energy conformer as a representative. Therefore, the rate constants were calculated by the multi‐structural TST. It was revealed that the differences in functional groups containing O atoms mainly affect the bond dissociation energies of the C–H bonds and the activation energies of hydrogen abstraction reactions only when the C atoms are adjacent to the O atoms. Additionally, it was found that hydrogen bonds formed in the TSs show minor effect on rate parameters for the overall rate constants, apart from the reduction of the pre‐exponential factors for the H‐abstraction reactions from the methylene position of ethyl groups. The comparison with the rate constants from previous studies showed reasonable results, indicating that the rate constants in this study, which thoroughly consider rotational conformers, can be the current best estimates. [ABSTRACT FROM AUTHOR]

Meerwein-Ponndorf-Verley (MPV) reduction is a highly selective, heterogeneously catalyzed process for the synthesis of alcohols from aldehydes and ketones under relatively mild reaction conditions. The reduction of the carbonyl group involves the transfer of a hydrogen atom from the alcohol, which, acts as a sacrificial reducing agent. Thanks to its simplicity and high variability and applicability, MPV has remained relevant over time. Recently, MPV has even become a cornerstone of basic organic chemistry, playing a key role in several cascade reactions in biomass transformation. Yet, despite extensive research on MPV, important questions are still unanswered, such as the specific role of acid and basic sites in the overall catalytic process. Here, we review advances on MPV made in the last 15 years, focusing on the catalytic materials and their properties and addressing topics ranging from classical metal oxide catalysis to new catalytic systems tested in MPV, including the synthesis of valuable products. This review is divided into four sections, namely the (1) introduction, summarizing the typical features of MPV, (2) classical studies on MPV, highlighting carbonyl group reduction as the conventional approach to synthesizing alcohols, and (3) MPV in biomass transformation, examining new applications of MPV in cascade reactions for biomass conversion into molecular platforms, followed by (4) conclusions and future perspectives on MPV heterogeneous catalysis reduction. Overall, the state of the art on MPV underscores the utility, potential and importance of this reaction not only for classical carbonyl reduction but also for biomass transformation over a wide range of catalytic materials and with various substrates. [ABSTRACT FROM AUTHOR]

The activation of inert C–H bonds remains a challenge in current chemistry. Here, we report the excellent reactivity of the anionic gallylene species [LGa:][Na(THF)3] (L = [(2,6-iPr2C6H3)NC(CH3)]22−, 1) that allows the selective activation one ortho sp2 C–H bond of several azobenzene and azide derivatives at ambient temperature, with the transfer of the hydrogen atom to one of the nitrogen atoms. The process leads to the formation of the aryl amido products [LGa-κ2N,C-PhNN(H)(p-R-C6H3)][Na(solvent)3] (2, R = H solvent = DME (1,2-Dimethoxyethane); 3, R = –OMe, solvent = DME; 4, R = –NMe2 solvent = THF), [LGa-κ2N,C-(m-CH3-C6H4)NN(H)(m-CH3-C6H3)][Na(15-C-5)2] (5) with new Ga–C and Ga–N bonds. Moreover, 1 is also effective for the C–H activation of two azides RN3 (R = 2,4,6-Me3C6H2 or 2,6-iPr2C6H3), resulting in the formation of gallium amides [LGa(NH-2-(CH2)-4,6-Me2C6H2)][Na(15-C-5)2] (6) and [LGa(NH-2,6-iPr2C6H3)2][Na(THF)5] (7) through intra- or intermolecular sp3 C–H amination. Significantly, these reactions occur for the highly challenging activation of inert C(sp2)–H and C(sp3)–H bonds, thus demonstrating the excellent reactivity of the Ga(I) species 1. The products 2–7 were characterized by X-ray crystallography, 1H and 13C NMR, UV–vis spectroscopy, and density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) serve as an excellent foundation for heterogeneous photocatalysis. Herein, we synthesized an anthraquinone‐based COF (TpAQ) on a gram scale via a mechanochemical grinding pathway. This COF was employed as a visible‐light‐harvesting photocatalyst for selective fluorination of benzylic C─H bonds and perfluoroalkylation of arenes. The carbonyl core in the anthraquinone linker facilitated benzylic fluorination through a hydrogen atom transfer (HAT) pathway. Control experiments and photophysical analysis were conducted to gain deeper insight into the reaction mechanism. The recyclability up to the fifth cycle without significant loss of yield (>90%) highlighted the robustness of the catalyst. This reaction strategy was also executed on a gram scale to validate the scalability of the protocol. [ABSTRACT FROM AUTHOR]

A visible‐light triplet photocatalyst 5‐acetyl‐2‐mercapto‐benzoic acid methyl ester (AcBSH) was developed through introducing acetyl into benzenethiolate to improve the efficiency of intersystem crossing (ISC) and using o‐methoxyformyl to increase the molar extinction coefficient. In the photocatalytic system of AcBSH, the reductive dearomatization of N‐arylformylindoles is achieved to afford the desired indolines in moderate to excellent yields, including both indoles without (1) and with 2‐substituent (2). The 2‐substituent is a steric hindrance for the conjugation between benzoyl and indole moiety, and makes indole 2 and indole 1 exhibit different reduction potentials (Ered) and different triplet energy levels (ΔET). Thereby, two kinds of substrates undergo primarily two photocatalytic pathways: i) successive SET/protonation pathway, which merging photosensitization via triplet‐triplet energy transfer (EnT) and photoinduced SET for substrates 1, and ii) single electron transfer (SET) from the triplet photocatalyst and a concerted hydrogen atom transfer (HAT) process for substrates 2. [ABSTRACT FROM AUTHOR]

Hydrogen atom transfer (HAT) from a metal-hydride is a reliable and powerful method for functionalizing unsaturated C–C bonds in organic synthesis. Cobalt hydrides (Co–H) have garnered significant attention in this field, where the weak Co–H bonds are most commonly generated in a catalytic fashion through a mixture of stoichiometric amounts of peroxide oxidant and silane reductant. Here we show that the reverse process of HAT to an alkene, i.e. hydrogen atom abstraction of a C–H adjacent to a radical, can be leveraged to generate catalytically active Co–H species in an application of shuttle catalysis coined shuttle HAT. This method obviates the need for stoichiometric reductant/oxidant mixtures thereby greatly simplifying the generation of Co–H. To demonstrate the generality of this shuttle HAT platform, five different reaction manifolds are shown, and the reaction can easily be scaled up to 100 mmol. Hydrogen atom transfer (HAT) from a metal-hydride is a reliable and powerful method for functionalizing unsaturated C–C bonds in organic synthesis. Herein, the authors show that reverse process of HAT to an alkene can be leveraged to generate catalytically active Co–H species in an application of shuttle catalysis coined shuttle HAT. [ABSTRACT FROM AUTHOR]

As nitrogen analogues of iron‐oxo species, high‐valent iron‐imido species have attracted great interest in the past decades. FeV‐alkylimido species are generally considered to be key reaction intermediates in Fe(III)‐catalyzed C(sp3)─H bond aminations of alkyl azides but remain underexplored. Here, it is reported that iron‐corrole (Cor) complexes can catalyze a wide range of intramolecular C─H amination reactions of alkyl azides to afford a variety of 5‐, 6‐ and 7‐membered N‐heterocycles, including alkaloids and natural product derivatives, with up to 3880 turnover numbers (TONs) and excellent diastereoselectivity (>99:1 d.r.). Mechanistic studies including density functional theory (DFT) calculations and intermolecular hydrogen atom abstraction (HAA) reactions reveal key reactive FeV‐alkylimido intermediates. The [FeV(Cor)(NAd)] (Ad = adamantyl) complex is independently prepared and characterized through electron paramagnetic resonance (EPR), resonance Raman (rR) measurement, and X‐ray photoelectron spectroscopy (XPS). This complex is reactive toward HAA reactions with kinetic isotope effects (KIEs) similar to [Fe(Cor)]‐catalyzed intramolecular C─H amination of alkyl azides. [ABSTRACT FROM AUTHOR]

The development of small organic molecules that can convert light energy into chemical energy to directly promote molecular transformation is of fundamental importance in chemical science. Herein, we report a zwitterionic acridinium amidate as a catalyst for the direct functionalization of aliphatic C−H bonds. This organic zwitterion absorbs visible light to generate the corresponding amidyl radical in the form of excited‐state triplet diradical with prominent reactivity for hydrogen atom transfer to facilitate C−H alkylation with a high turnover number. The experimental and theoretical investigations revealed that the noncovalent interactions between the anionic amidate nitrogen and a pertinent hydrogen‐bond donor, such as hexafluoroisopropanol, are crucial for ensuring the efficient generation of catalytically active species, thereby fully eliciting the distinct reactivity of the acridinium amidate as a photoinduced direct hydrogen atom transfer catalyst. [ABSTRACT FROM AUTHOR]

The document is the contents list for an issue of the journal Chemical Communications. It includes articles on various topics such as the synthesis of chiral systems, progress in extractants for actinides and lanthanides separation, and the design of sulfonimide anions for rechargeable lithium batteries. The journal is published by The Royal Society of Chemistry and aims to connect the world with the chemical sciences. [Extracted from the article]

Recent years have witnessed the emergence of direct intermolecular C(sp3)–H bond functionalization using in situ generated aryl/alkyl radicals as a unique class of hydrogen atom transfer (HAT) agents. A variety of precursors have been exploited to produce these radical HAT agents under photocatalytic, electrochemical or thermal conditions. To date, viable aryl radical precursors have included aryl diazonium salts or aryl azosulfones, diaryliodonium salts, O-benzoyl oximes, aryl sulfonium salts, aryl thioesters, and aryl halides; and applicable alkyl radical sources have included tetrahalogenated methanes (e.g., CCl3Br, CBr4 and CF3I), N-hydroxyphthalimide esters, alkyl bromides, and acetic acid. This review summarizes the current advances in direct intermolecular C(sp3)–H functionalization through key HAT events with in situ generated aryl/alkyl radicals and categorizes the procedures by the specific radical precursors applied. With an emphasis on the reaction conditions, mechanisms and representative substrate scopes of these protocols, this review aims to demonstrate the current trends and future challenges of this emerging field. [ABSTRACT FROM AUTHOR]

The kinetics of 16 H-atom abstraction reactions of C 1 -C 4 alkanes by ketenyl radical (HCCO) are studied to enhance the existing combustion mechanisms. Firstly, the obtain the lowest-energy conformer, vibration frequencies and single point energies for the reactants, prepolymers, transition states, and products are determined using the CCSD(T)/cc-pVQZ//B3LYP/6-311G+(d,p) theory level. Subsequently, temperature-dependent reaction rate constants for the major channels are predicted by the TST method. Finally, the H-atom abstraction reactions are validated under multiple temperature conditions, and the effects of the reactions on auto-ignition process and CO emission characteristics of n-heptane/NG mixture are researched. The results indicate that the H-atom abstraction reactions by Cα-atom play a significant role for the diesel/NG combustion. To combine the reaction pathways and rate constants into the existing kinetic mechanisms resulted in more accurate predictions of the ignition delay time. Furthermore, these kinetics data are valuable for revealing the CO emissions of the dual-fuel engines. • H-atom abstraction by Cα of HCCO is dominant at low temperatures. • Hydrogen abstraction reactions caused by O-atoms hardly occur below 1200 K. • The highly symmetrical structure of methane causes the rate of H-atom abstraction to be very sensitive to temperature change. • The addition of the H-atom abstraction reactions can improve the calculation accuracy of the ignition delay time up 9.3%. • The H-atom abstraction reactions inhibit the consumption of CO and enhance branch ratio of CH 2 CO.→CO [ABSTRACT FROM AUTHOR]

The valorization of toluene offers a dual solution by addressing its environmental impact while also facilitating the synthesis of a diverse array of valuable fine chemicals and pharmaceutical intermediates, thus ensuring both ecological sustainability and economic viability. We report herein a synergistic approach that harmonizes hydrogen atom transfer (HAT) process with the generation of reactive oxygen species (ROS) under mild condition and low catalyst loading, which enables the efficient synthesis of a broad spectrum of esteemed benzoic acid derivatives and aryl ketones through the photocatalytic oxidation of toluene derivatives. Mechanistic elucidation reveals that the HAT reagent anthraquinone has both the capabilities to abstract hydrogen atoms and the ability to generate singlet oxygen (1O2) during energy transfer with triplet oxygen (3O2), and the combination of these two potencies significantly improves the catalytic efficiency of the reaction. This study not only introduces the amalgamation of HAT with ROS generation but also delineates a systematic approach for the selection of HAT reagents with energy transfer proficiency for ROS generation in catalytic oxidation reactions. [ABSTRACT FROM AUTHOR]

The escalating demand for plastics has resulted in a surge of plastic waste worldwide, posing a monumental environmental challenge. To address this issue, a versatile photo‐oxidative degradation method applicable to seven distinct polymer families is proposed, comprising poly(isobutyl vinyl ether) (PIBVE), poly(2,3‐dihydrofuran) (PDHF), poly(vinyl acetate) (PVAc), poly(n‐butyl acrylate) (PBA), poly(methyl acrylate) (PMA), poly(vinyl chloride) (PVC), poly(dimethyl acrylamide) (PDMA), poly(ethylene oxide) (PEO), poly(oligo(ethylene glycol) methyl ether acrylate) (PEGMEA), and even poly(methyl methacrylate) (PMMA). This method employs photo‐mediated hydrogen atom transfer (HAT) followed by oxidation to promote polymer degradation. This reaction is carried out under aerobic condition in the presence of iron trichloride (FeCl3) as a photocatalyst in combination with low‐intensity purple light irradiation. The process can degrade up to 97% of the polymer in less than 3 h. This degradation process can be easily controlled by switching the light off, which allows for precise modulation of the degradation rate, enhancing the effectiveness of the method. Overall, this method provides a sustainable method for degrading various polymer types with low energy input. [ABSTRACT FROM AUTHOR]

A straightforward method for the dehydrogenative alkylation of quinoxalin-2(1H)-ones with alkylbenzenes has been developed, facilitated by a photoexcited nitroarene. The reaction's success hinges on the dual role of the photoexcited nitroarene molecule, acting as both a hydrogen atom transfer (HAT) reagent and an oxidant. This technique is both atom-economical and cost-effective, due to the readily available nitroarene, which serves as the sole intermediary in the reaction process. [ABSTRACT FROM AUTHOR]

Activation and selective oxidation of inert C(sp3)–H bonds remain one of the most challenging tasks in current synthetic chemistry due to the inherent inertness of C(sp3)–H bonds. In this study, inspired by natural monooxygenases, we developed a coordination polymer with naphthalenediimide (NDI)-based ligands and binuclear iron nodes. The mixed-valence FeIIIFeII species and chlorine radicals (Cl•) are generated via ligand-to-metal charge transfer (LMCT) between FeIII and chlorine ions. These Cl• radicals abstract a hydrogen atom from the inert C(sp3)–H bond of alkanes via hydrogen atom transfer (HAT). In addition, NDI converts oxygen to 1O2 via energy transfer (EnT), which then coordinates to FeII, forming an FeIV = O intermediate for the selective oxidation of C(sp3)–H bonds. This synthetic platform, which combines photoinduced EnT, LMCT and HAT, provides a EnT-mediated parallel multiphoton excitation strategy with kinetic synergy effect for selective C(sp3)–H oxidation under mild conditions and a blueprint for designing coordination polymer-based photocatalysts for C(sp3)–H bond oxidation. Activation and selective oxidation of inert C(sp3)–H bonds remain one of the most challenging tasks in current synthetic chemistry. Here, the authors develop a coordination polymer with naphthalenediimide-based ligands and binuclear iron nodes for the oxidation of C(sp3)-H bonds. [ABSTRACT FROM AUTHOR]

A copper catalyzed aerobic formal addition of aliphatic C(sp3)−H bonds to alkenes via a phenyl radical mediated intermolecular HAT process is reported herein, in which the phenylhydrazine not only acts as a HAT reagent precursor, but also as a hydrogen atom donor. This reaction affords an alternative method for the direct formal addition of aliphatic C(sp3)−H bonds to alkenes utilizing air as the radical initiator without additional reductants at ambient temperature. A variety of alkanes and electron‐deficient alkenes are successfully incorporated, furnishing a series of aliphatic C(sp3)−H formal addition products in 20–93% yield. Preliminary mechanistic studies show that the 2‐tetrahydrofuranyl and phenyl radical are formed in this reaction. [ABSTRACT FROM AUTHOR]

A mild, metal‐free Giese‐type hydrodifluoroalkylation of electron‐deficient alkenes under visible‐light irradiation has been developed. This highly reducing photoactivated Hantzsch ester facilitates C(sp3)−CF2 bond formation through photoinduced electron transfer (PET) and hydrogen atom transfer (HAT) processes, providing an easy access to diverse gem‐difluorinated alkanes. [ABSTRACT FROM AUTHOR]

A highly efficient and sustainable approach was developed for the construction of Si–O/Si–Si bonds, through the electrochemical oxidative dehydrogenation of hydrosilanes with O-nucleophiles (e.g. phenols, naphthols, alcohols, and H2O) or hydrosilane self-condensation. The protocol employs a highly electrically conductive and recyclable ionic liquid as a catalyst, thus eliminating the need for external electrolytes and hydrogen atom transfer (HAT) agents. The ionic liquid could be easily recovered and reused for at least eight cycles with consistent performance. Notably, this electrochemical method exhibits a broad substrate scope and high functional-group compatibility (66 examples, up to 96% yield). Initial mechanistic studies show that silicon radicals are generated via the process of hydrogen atom transfer between bromine radicals and silanes, and KIE experiments demonstrate that Si–H bond cleavage is the rate-determining step of the reaction. [ABSTRACT FROM AUTHOR]

The evolution of catalysis and functional group transfer reagents play a significant role in the development of anti‐Markovnikov alkene hydrofunctionalization reactions, facilitating the access to value‐added molecules. We herein report the first rational design of a modular intermolecular anti‐Markovnikov hydronitration of alkenes, enabling the direct synthesis of terminal nitroalkanes under visible light‐mediated photoredox catalysis. By employing the redox‐active organic nitrating reagent N‐nitrosuccinimide, the produced nitryl radicals, in the presence of an olefin and a hydrogen atom transfer (HAT) mediator, lead to an anti‐Markovnikov addition with complete regioselectivity. Furthermore, we present results demonstrating the use of this catalytic system for chain expansion via anti‐Markovnikov addition, utilizing substituted bromonitroalkanes as commercially available reagents. These transformations effectively address a gap in synthetic chemistry, enabling the direct synthesis of nitroalkanes from a variety of unactivated olefins in both complex molecules and unfunctionalized commodity chemicals. [ABSTRACT FROM AUTHOR]

Nonsymmetrical oxygen-bridged binuclear copper centers have been proposed and modeled as intermediates and transition states in several C-H oxidation pathways, leading to the postulation that structural dissymmetry enhances the reactivity of the bridging oxygen. However, experimentally characterizing the structure and reactivity of these transient species is remarkably challenging. Here, we report the high-pressure synthesis of a metastable nonsymmetrical dicopper-µ-oxo compound with exceptional reactivity toward the mono-oxygenation of aliphatic C-H bonds. The nonequivalent coordination environment of copper stabilizes localized mixed valency and greatly enhances the hydrogen atom abstraction activity of the bridging oxygen, enabling room-temperature hydroxylation of methane under pressure. These findings highlight the role of dissymmetry in the reactivity of binuclear copper centers and demonstrate precise control of molecular structures by mechanical means. [ABSTRACT FROM AUTHOR]

The document is the contents list for the journal "Chemical Communications" published on October 4, 2024. It includes various articles and communications on topics such as solar energy, catalysis, coordination chemistry, and organic synthesis. The journal is published by The Royal Society of Chemistry, a leading chemistry community. The document provides a comprehensive overview of the articles included in the issue, allowing library patrons to quickly identify relevant research topics. [Extracted from the article]

Described herein is a novel visible-light-promoted three-component radical iodo-alkylative cyclization of alkynes using iodoform as a bifunctional iodine atom source. Visible-light irradiation of a polar–polar interaction complex of iodoform with malonate enables the cooperative hydrogen atom transfer process to generate alkyl radical and trigger a cascade reaction sequence. [ABSTRACT FROM AUTHOR]

Exposure of water to ionizing radiation induces OH radical formation. Within cellular environments, the presence of OH radicals can stimulate the abstraction of hydrogen atoms from the sugar backbone of DNA. Subsequent damage to DNA structures leads to various diseases. Multiple studies have elucidated this phenomenon, especially computational studies examining the differences in the degree of abstraction between the sugar hydrogens (H1′, H2′, H2″, H3′, H4′, H5′, and H5″). However, the details of this phenomenon have not yet been clarified. It is rare for OH radicals to approach DNA within the simulation time, making it difficult to adequately sample the configurations in which OH radicals immediately precede the abstraction of the hydrogen atoms. To address this problem, we performed molecular dynamics simulation to calculate the relative accessibility by putting a potential on nucleotides and OH radicals. As a result, we found that the accessibility of OH radicals to each hydrogen atom differs from that of water molecules as solvents. A more detailed accessibility analysis revealed that the angle of the OH radicals approaching the hydrogen atoms of ribose and the energy barrier for abstracting the hydrogen atoms can be considered to improve the correspondence with the experimental data. Moreover, we found that the behavior of water molecules and OH radicals toward accessibility to DNA differs significantly and showed that the factors are related to the physicochemical properties of water molecules and OH radicals, as well as the structure of DNA. [ABSTRACT FROM AUTHOR]

Fluorine's high electronegativity, lipophilicity, and metabolic stability make it a valuable element for drug design and development. Consequently, significant synthetic efforts have focused on introducing fluorine and fluorinated motifs into organic molecules, with the synthesis of trifluoromethyl ketones (TFMKs) recently attracting considerable attention. Building on our ongoing research on radical organofluorine chemistry, we present herein the divergent synthesis of trifluoromethyl ketones directly from olefins using readily available chloro‐ and bromotrifluoroacetone as synthetic precursors of the trifluoroacetonyl radical under photoredox catalysis. Mechanistic studies revealed that the divergence is attained through radical polar crossover (RPC) and hydrogen atom transfer (HAT) mechanisms. [ABSTRACT FROM AUTHOR]

Context: Recently, a few antiviral drugs viz Molnupiravir (EIDD-1931), Favipiravir, Ribavirin, Sofosbuvir, Galidesivir, and Remdesivir are shown to be beneficial against COVID-19 disease. These drugs bind to the viral RNA single strand to inhibit the virus genome replication. Similarly, recently, some artificial nucleotides, such as P, J, B, X, Z, V, S, and K were proposed to behave as potent antiviral candidates. However, their activity in the presence of the most reactive hydroxyl (OH) radical is not yet known. Here, the possibility of RNA strand break due to the OH radical-induced C1′-hydrogen (H) abstraction reaction of the above molecules (except Remdesivir) is studied in detail by considering their nucleotide conformation. The results are compared with those of the natural RNA nucleotides (G, C, A, and U). Due to low Gibbs barrier-free energy and high exothermicity, all these nucleotides (except Remdesivir) are prone to OH radical-induced C1′-H abstraction reaction. As Remdesivir contains a C1′-CN bond, the OH radical substitution reactions at the CN and C1′ sites would likely liberate the catalytically important CN group, thereby downgrading its activity. Method: Initially, the B3LYP-D3 dispersion-corrected density functional theory method and 6–31 + G* basis set were used to optimize all reactant, transition state, and product complexes in the implicit aqueous medium. Subsequently, the structures of these complexes were further optimized by using the ωB97X-D dispersion-corrected density functional theory method and cc-PVTZ basis set in the aqueous medium. The IEFPCM method was used to model the aqueous medium. [ABSTRACT FROM AUTHOR]

The dehydrogenative coupling of alcohols and amines to form amide bonds is typically catalysed by homogeneous transition metal catalysts at high temperatures ranging from 130–140 °C. In our pursuit of an efficient and recyclable photocatalyst capable of conducting this transformation at room temperature, we report herein a COF‐mediated dehydrogenative synthesis. The TTT‐DHTD COF was strategically designed to incorporate a high density of functional units, specifically dithiophenedione, to trap photogenerated electrons and effectively facilitate hydrogen atom abstraction reactions. The photoactive TTT‐DHTD COF, synthesized using solvothermal methods showed high crystallinity and moderate surface area, providing an ideal platform for heterogeneous amide synthesis. Light absorption by the COF across the entire visible range, narrow band gap, and valence band position make it well‐suited for the efficient generation of excitons necessary for targeted dehydrogenation. Utilizing red light irradiation and employing extremely low loading of the COF, we have successfully prepared a wide range of amides, including challenging secondary amides, in good to excellent yields. The substrates' functional group tolerance, very mild reaction conditions, and the catalyst's significant recyclability represent substantial advancements over prior methodologies. [ABSTRACT FROM AUTHOR]

During thermal utilization of biomass, a complex array of reactions ensues in the oxidative environment between fragments of the biomass and reactive species. In the low-temperature window, hydroperoxyl (HO 2) radicals assume a central role prior to the establishment of the O/H radical pool. Anisole, cresol, guaiacol and vanillin are often utilized as representative model compounds to comprehend the combustion chemistry of the phenolic entities in biomass and oxygen-containing derived bio-oil. This paper reports thermo-kinetic parameters for the reactions of HO2 radicals with anisole, cresol, guaiacol and vanillin. Computed activation enthalpies entail facile values for H abstraction from the side-chain functional groups in the investigated compounds. H abstraction from the hydroxyl groups incurs lower activation energies in reference to methyl sites in cresol and guaiacol. Hence, H abstraction from the OH sites in these two molecules proceeds at a faster reaction rate constant when compared to abstraction from the methyl site. In the vanillin molecule, abstraction from the aldehydic and hydroxyl sites portrays comparable importance. The effect of scaling vibrational frequencies and the type of applied quantum tunneling on the computed reaction rate constants were thoroughly explored. Analysis of entropies of activation indicates that the transition states exhibit a product-like character. While ignition delay times of fuels often exhibit a profound sensitivity towards initial H abstraction reactions by HO2, we found that ignition delay times of the four title molecules remain almost unchanged when updating literature kinetics models with new reaction rate constants calculated herein. It is anticipated that reported outcomes from this study aid in formulating a better understanding of the complex chemical reactions that dictate oxidative decomposition of oxygenated bio-oil model compounds. The work reports thermo-kinetic parameters for the reactions of HO2 radicals with prominent biomass model compounds. Abstraction from various sites have been explored. The effect of the title reaction in the ignition delay times of these compounds is rather limited. [ABSTRACT FROM AUTHOR]

Hibiscetin, a major bioactive ingredient of Hibiscus sabdariffa, exhibits numerous pharmacological actions and five metal-chelating sites. Since flavonoids play a vital role in scavenging or reducing the toxicity of redox-active metal ions, the chelation of Fe2+ cation by the flavonoid Hibiscetin was examined using the DFT method carried out at the M06-2X/6-311+G(d, p)/LANL2DZ level of theory in the aqueous phase. All the complexed species derived from neutral and deprotonated ligand forms were considered. The results show that the oxygen atoms of the di-deprotonated catechol moiety at the C-7 and C-8 positions of Hibiscetin interact best with the Fe2+ ion among the possible chelation sites on Hibiscetin. The stability of the most stable complex, HIB-[7-8] -Fe2+, was validated by Frontier molecular orbital, Natural bond orbital, and natural population reports. The topological analysis indicated the electrostatic interaction between the oxygen atoms of Hibiscetin and the metal ion in the complex. The investigation of the radical scavenging capabilities in gas, water, and benzene media proved the superior antioxidant activity of the most stable complex of Hibiscetin and Fe2+ ion when compared to parent flavonoid. The hydrogen atom transfer (HAT), single-electron transfer followed by proton transfer (SET-PT), and sequential proton-loss electron transfer (SPLET) mechanisms were studied, and the HAT mechanism was found to be the most effective radical scavenging mechanism in the gas and non-polar solvent and the SPLET mechanism in the polar solvent. The best site for radical attack is identified to be 4'-OH. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: A visible light photocatalytic [3+2] cycloaddition of alkynes with readily accessible organic iodides as the C3 synthon is developed herein. By merging halogen atom transfer (XAT) and hydrogen atom transfer (HAT), alkyl/aryl iodides serve as a formal diradical precursor and add across C‐C triple bonds to deliver a number of functionalized cyclopentanes in moderate to high yields with exceptional regio‐ and diastereoselectivity. A reductive radical‐polar crossover mechanism, involving the cascade XAT, radical addition, 1,5‐HAT, polar effect‐promoted 5‐endo annulation, single electron transfer (SET) reduction, and protonation, may account for this unprecedented dehalogenative [3+2] cycloaddition. This work not only expands the repertoire of the traditional RATC methodology, but also provides a robust platform for the expedient assembly of cyclopentanes, a valuable structural motif in the realms of medicinal chemistry and material sciences. [ABSTRACT FROM AUTHOR]

Machine learning combined with density functional theory (DFT) enables rapid exploration of catalyst descriptors space such as adsorption energy, facilitating rapid and effective catalyst screening. However, there is still a lack of models for predicting adsorption energies on oxides, due to the complexity of elemental species and the ambiguous coordination environment. This work proposes an active learning workflow (LeNN) founded on local electronic transfer features (e) and the principle of coordinate rotation invariance. By accurately characterizing the electron transfer to adsorption site atoms and their surrounding geometric structures, LeNN mitigates abrupt feature changes due to different element types and clarifies coordination environments. As a result, it enables the prediction of *H adsorption energy on binary oxide surfaces with a mean absolute error (MAE) below 0.18 eV. Moreover, we incorporate local coverage (θ1) and leverage neutral network ensemble to establish an active learning workflow, attaining a prediction MAE below 0.2 eV for 5419 multi-*H adsorption structures. These findings validate the universality and capability of the proposed features in predicting *H adsorption energy on binary oxide surfaces. [ABSTRACT FROM AUTHOR]

This paper highlights the latest advancements in asymmetric alkylative difunctionalization of carbon–carbon double bonds by utilizing aliphatic C─H substrates as alkyl radical precursors. By integrating different hydrogen atom transfer (HAT) processes with various transition metal catalytic systems, various alkane substrates can be efficiently converted into corresponding alkyl radicals, which then participate in radical additions to carbon–carbon double bonds followed by stereoselective functionalizations with a third component. These strategies leverage inexpensive, abundant, and readily available alkane feedstocks to rapidly construct complex chiral molecules, demonstrating high step and atom economy. This paper focuses on recent progress and applications in this area, provides a comprehensive perspective on current developments, and suggests future directions in alkane‐involved asymmetric transformations. [ABSTRACT FROM AUTHOR]

In this study, we investigate the protonation effects on the structure, relative stability and basicity of complexes formed by the interaction of monomers and dimers of BeX2 and MgX2 (X = H, F) with NH3, CH2NH, HCN, and NC5H5 bases. Calculations were performed using the M06‐2X/aug‐cc‐pVTZ formalism, along with QTAIM, ELF and NCI methods for electron density analysis and MBIE and LMO‐EDA energy decomposition analyses for interaction enthalpies. The protonation of the MH2– and M2H4–Base complexes occurs at the negatively charged hydrogen atoms of the MH2 and M2H4 moieties through typical hydride abstraction reactions, while protonation at the N atom of the base is systematically less exothermic. The preference for the hydride transfer mechanism is directly associated with the significant exothermicity of H2 formation through the interaction between H− and H+, and the high hydride donor ability of these complexes. The basicity of both, MH2 and M2H4 compounds increases enormously upon association with the corresponding bases, with the increase exceeding 40 orders of magnitude in terms of ionization constants. Due to the smaller exothermicity of HF formation, the basicity of fluorides is lower than that of hydrides. In Be complexes, the protonation at the N atom of the base dominates over the fluoride abstraction mechanism. However, for the Mg complexes the fluoride abstraction mechanism is energetically the most favorable process, reflecting the greater facility of Mg complexes to lose F−. [ABSTRACT FROM AUTHOR]

Natural photosynthesis enzymes utilize energies of several photons for challenging oxidation of water, whereas artificial photo‐catalysis typically involves only single‐photon excitation. Herein, a multiphoton excitation strategy is reported that combines parallel photo‐excitations with a photoinduced electron transfer process for the activation of C(sp3)─H bonds, including methane. The metal–organic framework Fe3‐MOF is designed to consolidate 4,4′,4″‐nitrilotrisbenzoic units for the photoactivation of dioxygen and trinuclear iron clusters as the HAT precursor for photoactivating alkanes. Under visible light irradiation, the dyes and iron clusters absorbed parallel photons simultaneously to reach their excited states, respectively, generating 1O2 via energy transfer and chlorine radical via ligand‐to‐metal charge transfer. The further excitation of organic dyes leads to the reduction of 1O2 into O2•− through a photoinduced electron transfer, guaranteeing an extra multiphoton oxygen activation manner. The chlorine radical abstracts a hydrogen atom from alkanes, generating the carbon radical for further oxidation transformation. Accordingly, the total oxidation conversion of alkane utilizing three photoexcitation processes combines the energies of more than two photons. This new platform synergistically combines a consecutive excited photoredox organic dye and a HAT catalyst to combine the energies of more than two photons, providing a promising multiphoton catalysis strategy under energy saving, and high efficiency. [ABSTRACT FROM AUTHOR]

The γ C-H amination of carboxylic acid presents a promising and sustainable strategy for synthesizing high-value pharmaceutical chemicals. Radical reaction pathways initiated by aroyloxy radical-involved hydrogen atom transfer (HAT) provide diverse but challenging opportunities for remote C-H functionalization. In this report, the first example of intramolecular γ C-H amination of carboxylic acids using a commercially available oxime auxiliary has been achieved. This innovative approach employs a radical relay chaperone, facilitating selective C-H functionalization via 1,5-HAT/radical cross-coupling and enabling the net incorporation of ammonia at the γ carbon of carboxylic acids. In addition, this protocol enables the recycling of the by-product benzophenone, and both product isolation and by-product recycling are silica gel-free. The reactions offer high chemo- and regio-selectivities, operate under mild reaction conditions, boast a broad substrate scope, exhibit good functional group compatibility, and are easily scalable. [ABSTRACT FROM AUTHOR]