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Iron‐catalyzed C−H amination is emerging as an attractive and sustainable method to install amine functionalities into organic compounds. Amination of C(sp3)−H bonds is usually mediated by an iron‐nitrene intermediate via a Hydrogen Atom Abstraction/Radical Recombination mechanism reminiscent of biomimetic C−H oxidation. Accordingly, this transformation can be catalyzed by engineered iron enzymes, heme and nonheme iron complexes as well as iron salts, although it is often limited to intramolecular reactions and/or activated positions. Aromatic C(sp2)−H amination is mediated by addition of electrophilic iron nitrenes or protonated N‐radical intermediates (produced with Fe catalysts) to aromatic systems. Again, high selectivity is obtained via (pseudo) intramolecular reactions. From a mechanistic perspective, several iron nitrene intermediates have been isolated and characterized over the years in different ligand scaffolds and iron oxidation states. Structure‐activity correlations have been drawn only in few cases and point to a key role of the spin density on the nitrene ligand and of the iron oxidation state. This review describes the state of the art for homogeneous iron catalyzed C(sp3)−H and C(sp2)−H amination focusing on the last 5 years (2019–2023) from a mechanism‐driven catalyst design perspective. [ABSTRACT FROM AUTHOR]

Sulfilimines and their derivatives have garnered considerable interest in both synthetic and medicinal chemistry. Photochemical nitrene transfer to sulfides is known as a conventional synthetic approach to sulfilimines. However, the existing methods have a limited substrate scope stemming from the incompatibility of singlet nitrene intermediates with nucleophilic functional groups. Herein, we report the synthesis of N‐sulfonyl sulfilimines via visible‐light‐mediated energy transfer to sulfonyl azides, uncovering the previously overlooked reactivity of triplet nitrenes with sulfides. This reaction features broad functional group tolerance, water compatibility, and amenability to the late‐stage functionalization of drugs. Thus, this work represents an important example of energy transfer chemistry that overcomes challenges in traditional synthetic methods. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Nitrenes, as neutral monovalent nitrogen‐centered molecular species, can insert into various bond or remove nitrogen atoms from amines. Nitrene assisted single‐atom skeletal editing, discovered decades ago, provides an efficient approach for the precise alteration of cyclic skeletons. In this review, we briefly summarize early studies on skeletal editing of cyclic frameworks involving nitrene species, and introduce several recent important advances systematically. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of substituted ß-homoprolines using rhodium catalysis. ß-Homoproline is a variant of ¿-proline and is found in natural products and pharmaceuticals. The article describes the development of a new method for synthesizing ß-homoprolines, which involves the cyclization of isoxazolidin-5-ones using a rhodium catalyst. The authors demonstrate the scope and limitations of this method and discuss the downstream transformations that can be performed on the resulting ß-homoprolines. Overall, this research provides valuable insights into the synthesis and potential applications of ß-homoprolines. [Extracted from the article]

A series of terminal mono‐ and disubstituted beryllium azides of the form [(CAAC)Be(N3)R] (R=CAACH, Dur; CAACH/CAAC=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐yl/idene, Dur=2,3,5,6‐tetramethylphenyl) and [L2Be(N3)2] (L=CAACNH=1‐(2,6‐diisopropylphenyl)‐3,3,5,5‐tetramethylpyrrolidin‐2‐imine, IiPrMe=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene), respectively, were synthesized and characterized by NMR spectroscopy and X‐ray crystallography. Thermolysis and photolysis products of these first examples of tricoordinate azidoberyllium complexes evidence extensive ligand scrambling and the formal insertion of nitrenes into the CAAC−Be bond, generating cyclic alkyl(amino)imine (CAAI) ligands. Furthermore, the reaction with a small N‐heterocyclic carbene (NHC) leads to unexpected CAAC‐NHC ligand exchange, while the reaction with pentaphenylborole yields the first γ‐azide adduct of a borole, long postulated to be the first step in the synthesis of 1,2‐azaborinines from boroles and azides. [ABSTRACT FROM AUTHOR]

A facile and novel method was established for the synthesis of triazolinone scaffolds through [3 + 2] cycloaddition of C,N-cycloazomethylimines with dioxazolones in the presence of CH3ONa. In these transformations, isocyanates were formed in situ by the decarboxylation and Curtius rearrangement of dioxazolones. Importantly, the isocyanate formed from dioxazolone is employed for the first time for the cyclization instead of the widely used N-acyl nitrenes. The newly developed [3 + 2] cycloaddition is applicable to a broad range of substrates with high functional group tolerance, providing various triazolinones in good to excellent yields (up to 94%). Additionally, this method is easy to operate, green, environmentally friendly, and avoids highly toxic reagents. [ABSTRACT FROM AUTHOR]

Phosphinidenes are heavy congeners of nitrenes that have been broadly used as in situ reagents in synthetic phosphorus chemistry and also serve as versatile ligands in coordination with transition metals. However, the detection of free phosphinidenes is largely challenged by their high reactivity and also the lack of suitable synthetic methods, rendering the knowledge about the fundamental properties of this class of low‐valent phosphorus compounds limited. Recently, an increasing number of free phosphinidenes bearing prototype structural and bonding properties have been prepared for the first time, thus enabling the exploration of their distinct reactivity from the nitrene analogues. This Concept article will discuss the experimental approaches for the generation of the highly unstable phosphinidenes and highlight their distinct reactivity from the nitrogen analogues so as to stimuate future studies about their potential applications in phosphorus chemistry. [ABSTRACT FROM AUTHOR]

The Pauson-Khand reaction has in the past 50 years become one of the most common cycloaddition reactions in chemistry. Coupling two unsaturated bonds with carbon monoxide, the transformation remains limited to CO as a C1 building block. Herein we report analogous cycloaddition reactions with nitrenes as an N1 unit. The reaction of a nonconjugated diene with a nitrene precursor produces bicyclic bioisosteres of common saturated heterocycles such as piperidine, morpholine, and piperazine. Experimental and computational mechanistic studies support relaying of the diradical nature of triplet nitrene into the p-system. We showcase the reactionÕs utility in late-stage functionalization of drug compounds and discovery of soluble epoxide hydrolase inhibitors. [ABSTRACT FROM AUTHOR]

The given text provides information about the synthesis and characterization of various compounds. The compounds were prepared using a general procedure and purified by flash chromatography. The yield, physical properties, and spectroscopic data of each compound are provided. The compounds synthesized include N-Cyclohexyl-N-methyl-4-((3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-7-yl)oxy)butanamide, 6-Methyl-2H-benzo[b][1,4]oxazin-3(4H)-one, 6-Ethyl-2H-benzo[b][1,4]oxazin-3(4H)-one, 6-Propyl-2H-benzo[b][1,4]oxazin-3(4H)-one, 6-Methoxy-2H-benzo[b][1,4]oxazin-3(4H)-one, 1-Oxa-4-azaspiro[4.5]deca-6,9-diene-3,8-dione, 7-Fluoro-2H-benzo[b][1,4]oxazin-3(4H)-one, and 6-Fluoro-2H-benzo[b][1,4]oxazin-3(4H)-one. [Extracted from the article]

Catalytic C−N bond formation by direct activation of C−H bonds offers wide synthetic potential. En route to C−H amination, complexes with organic azides are critical precursors towards the reactive nitrene intermediate. Despite their relevance, α‐N coordinated organoazide complexes are scarce in general, and elusive with iron, although iron complexes are by far the most active catalysts for C−H amination with organoazides. Herein, we report the synthesis of a stable iron α‐N coordinated organoazide complex from [Fe(N(SiMe3)2)2] and AdN3 (Ad=1‐adamantyl) and its crystallographic, IR, NMR and zero‐field 57Fe Mössbauer spectroscopic characterization. These analyses revealed that the organoazide is in fast equilibrium between the free and coordinated state (Keq=62). Photo‐crystallography experiments showed gradual dissociation of N2, which imparted an Fe−N bond shortening and correspond to structural snapshots of the formation of an iron imido/nitrene complex. Reactivity of the organoazide complex in solution showed complete loss of N2, and subsequent formation of a C−H aminated product via nitrene insertion into a C−H bond of the N(SiMe3)2 ligand. Monitoring this reaction by 1H NMR spectroscopy indicates the transient formation of the imido/nitrene intermediate, which was supported by Mössbauer spectroscopy in frozen solution. [ABSTRACT FROM AUTHOR]

ortho‐Aminophenols are aromatic derivatives featuring vicinal N‐ and O‐based functionalities commonly found in the structures of many high‐value materials. These molecules are generally prepared using multistep strategies that follow the rules of electrophilic aromatic substitution (SEAr) chemistry. Despite their high fidelity, such approaches cannot target substrates featuring a "contra‐SEAr" arrangement of N‐ and O‐groups. Here we report an alternative strategy for the preparation of such ortho‐aminophenols using aryl azides as the precursors. The process utilizes low‐energy photoexcitation to trigger the decomposition of aryl azides into singlet nitrenes that undergo a dearomative‐rearomative sequence. This allows the incorporation of alcoholic nucleophiles into a seven‐membered ring azepine intermediate via temporary disruption of aromaticity, followed by electrophile‐induced re‐aromatization. The net retrosynthetic logic is that the alcohol displaces the azide, which, in turn, moves to its ortho position and furthermore is converted into an amide. The synthetic value and complementarity of this strategy has been demonstrated by the coupling of aryl azides with complex, drug‐like alcohols and phenols as well as amines, thiols and thiophenols, which provides a general platform for the fast and selective heterofunctionalization of aromatics. [ABSTRACT FROM AUTHOR]

Attaching a nitrene precursor to an intramolecular nucleophile allows for a catalytic asymmetric intramolecular oxyamination of alkenes in which the nucleophile adds in an endocyclic position and the amine in an exocyclic fashion. Using chiral‐at‐ruthenium catalysts, chiral γ‐aminomethyl‐γ‐lactones containing a quaternary carbon in γ‐position are provided in high yields (up to 99 %) and with excellent enantioselectivities (up to 99 % ee). DFT calculations support the possibility of both a singlet (concerted oxyamination of the alkene) and triplet pathway (stepwise oxyamination) for the formation of the predominant stereoisomer. γ‐Aminomethyl‐γ‐lactones are versatile chiral building blocks and can be converted to other heterocycles such as δ‐lactams, 2‐oxazolidinones, and tetrahydrofurans. [ABSTRACT FROM AUTHOR]

The azoxy functional group is an important structural motif and represents the formally oxidized counterpart of the azo group. Azoxy compounds find numerous applications ranging from pharmaceuticals to functional materials, yet their synthesis remains underdeveloped with a main focus on the formation symmetric azoxy compounds. To overcome challenges in the synthesis of such unsymmetric azoxy compounds, we designed a process employing readily accessible nitroso compounds and iminoiodinanes. This method builds on the use of visible light irradiation to generate a triplet nitrene from iminoiodinanes, which is trapped by nitroso arenes to give access to sulfonyl‐protected azoxy compounds with a good substrate scope and functional group tolerance. We further describe two applications of these sulfonyl‐protected azoxy compounds as radical precursors in synthesis, where the whole azoxy group can be transferred and employed in C(sp3)−H functionalization of ethers or 1,2‐difunctionalization of vinyl ethers. All of the reactions occurred at room temperature under visible light irradiation without the addition of any photoredox catalysts and additives. Control experiments, mechanism investigations, and DFT studies well explained the observed reactivity. [ABSTRACT FROM AUTHOR]

N-heterocycles are key building blocks for many pharmaceutical products. An efficient and sustainable method for the synthesis of this class of compounds consists of the recently established intramolecular C–H amination reaction. Development of new iron-based catalysts for this transformation is of paramount importance. Herein, three major challenges in this field are addressed: the accessibility of the catalyst, the lack of mechanisticunderstanding, and the limited activity and robustness of the catalyst. These challenges are tackled by threedifferent catalysts. The first catalyst is the commercially available FeI2, that shows good activities, but is limitedto substrates with activated C–H bonds. The Fe(HMDS)2 catalyst is used to perfom in-depth mechanistic studies, revealing key intermediates of the C–H amination reaction. The third catalyst, featuring mesoionic carbene ligands, displays unprecedented activities and aminates various C–H bonds.

Transition‐metal nitrides/nitrenes are highly promising reagents for catalytic nitrogen‐atom‐transfer reactivity. They are typically prepared in situ upon optically induced N2 elimination from azido precursors. A full exploitation of their catalytic potential, however, requires in‐depth knowledge of the primary photo‐induced processes and the structural/electronic factors mediating the N2 loss with birth of the terminal metal‐nitrogen core. Using femtosecond infrared spectroscopy, we elucidate here the primary molecular‐level mechanisms responsible for the formation of a unique platinum(II) nitrene with a triplet ground state from a closed‐shell platinum(II) azide precursor. The spectroscopic data in combination with quantum‐chemical calculations provide compelling evidence that product formation requires the initial occupation of a singlet excited state with an anionic azide diradical ligand that is bound to a low‐spin d8‐configured PtII ion. Subsequent intersystem crossing generates the Pt‐bound triplet azide diradical, which smoothly evolves into the triplet nitrene via N2 loss in a near barrierless adiabatic dissociation. Our data highlight the importance of the productive, N2‐releasing state possessing azide ππ* character as a design principle for accessing efficient N‐atom‐transfer catalysts. [ABSTRACT FROM AUTHOR]

Comprehensive Summary: Enantioselective or enantioconvergent iron‐catalyzed ring‐closing C(sp3)‐H aminations of N‐aroyloxyurea through intermediate iron nitrene species provide chiral 2‐imidazolidinones in up to 99% yield and with up to 95% ee (40 examples). This is a rare example in which sustainable iron catalysis is combined with C(sp3)‐H amination and asymmetric catalysis. Chiral 2‐imidazolidinones are prevalent structural motifs in bioactive molecules and can also be hydrolyzed to valuable chiral vicinal diamines in a single step. [ABSTRACT FROM AUTHOR]

Until now, there has been very little experimental evidence for the existence of free arsinidenes and stibinidenes, apart from the hydrides, AsH and SbH. Here, we report on photogeneration of triplet ethynylarsinidene, HCCAs, and triplet ethynylstibinidene, HCCSb, from ethynylarsine and ethynylstibine, respectively, in solid argon matrices. The products were identified using infrared spectroscopy and the associated UV absorption spectra are interpreted with the aid of theoretical predictions. [ABSTRACT FROM AUTHOR]

High-spin products of photolysis of 1,3,5-triazido-2,4,6-trichlorobenzene in a 2-methyltetrahydrofuran solution frozen at 6 K has been studied using EPR spectroscopy in combination with quantum-chemical calculations. It has been found that the photolysis of this triazide leads to the formation of a mixture of triplet 1,3-diazido-2,4,6-trichlorophenyl-5-nitrene, quintet 1-azido-2,4,6-trichlorophenyl-3,5-dinitrene, and septet 2,4,6-trichlorophenyl-1,3,5-trinitrene. The solvent effect on the EPR spectra and the magnetic characteristics of nitrenes has been studied. [ABSTRACT FROM AUTHOR]

The interstellar candidate phosphorus mononitride PN, a metastable species, was generated through high‐vacuum flash pyrolysis of (o‐phenyldioxyl)phosphinoazide in cryogenic matrices. Although the PN stretching band was not directly detected because of its low infrared intensity and possible overlaps with other strong bands, o‐benzoquinone, carbon monoxide, and cyclopentadienone as additional fragmentation products were clearly identified. Moreover, an elusive o‐benzoquinone‐PN complex formed when (o‐phenyldioxyl)phosphinoazide was exposed to UV irradiation at λ=254 nm. Its recombination to (o‐phenyldioxyl)‐λ5‐phosphinonitrile was observed upon irradiation with the light at λ=523 nm, which demonstrates for the first time the reactivity of PN towards an organic molecule. Energy profile computations at the B3LYP/def2‐TZVP density functional theory level reveal a concerted mechanism. To provide further evidence, UV/Vis spectra of the precursor and the irradiation products were recorded and agree well with time‐dependent DFT computations. [ABSTRACT FROM AUTHOR]

Dioxazolones, which are potent amide precursors, have been widely explored for the formation of C–N bonds with the help of transition-metal catalysts. Here, we highlight our recent studies on the synthesis of N -aryl amides using dioxazolones and boronic acids in the presence of copper(I) chloride under mild conditions. The versatility of the developed reaction is demonstrated by its wide range of functional-group tolerances as well as the release of nontoxic carbon dioxide. Optimization screenings reveal that a fluorine additive improves the desired reactivity toward the intended transformation. The addition of triphenylphosphine results in an N -acyl iminophosphorane, suggesting the involvement of an N -acyl nitrene intermediate in this transformation. [ABSTRACT FROM AUTHOR]

The in‐depth study of electrochemical (EC) synthesis can require a powerful mass spectrometry (MS) analytical platform which can discover and identify fleeting intermediates in EC reactions. Here we report a floating electrolytic electrospray ionization (FE‐ESI) strategy that can perform EC processes in a floating electrolytic cell and monitor intermediates by high‐resolution MS. Compared with previous EC‐MS methods, a significant advantage of FE‐ESI‐MS is that it allows one to modulate the electrolytic and electrospray process individually, ensuring its high sensitivity in discovering intermediates and universality to investigate redox reactions in different scenarios. This powerful platform has been successfully used to investigate the EC reductive coupling of p‐tolylboronic acid and p‐nitrotoluene. A series of nitrene intermediates were discovered and identified by FE‐ESI‐MS, indicating that a hidden mechanism involving nitrene formation might play a key role in EC reductive coupling process. [ABSTRACT FROM AUTHOR]

Nitrenes and nitrenoids are highly reactive species and the proposed key intermediates in nitrogen‐containing heterocyclic compound synthesis. In this work, we developed a practical method for the synthesis of phenanthridines by the reaction of oximes and Grignard reagents (with or without diethylzinc) via ring‐expansion of magnesium coordinated nitrenoid complex as the key step. The method has been used to synthesize optically active planar chiral ferrocenyl phenanthridines. [ABSTRACT FROM AUTHOR]

We present a versatile one-pot synthesis method for creating surface-anchored orthogonal gradient networks using a small bi-functional gelator, 4-azidosulfonylphenethyltrimethoxysilane (4-ASPTMS). The sulfonyl azide (SAz) group of 4-ASPTMS is UV (≤254 nm) and thermally active (≥100 °C) and, thus, enables us to vary the cross-link density in orthogonal directions by controlling the activation of SAz groups via UV and temperature means. We deposit a thin layer (∼200 nm) of a mixture comprising ∼90% precursor polymer and ∼10% 4-ASPTMS in a silicon wafer. Upon UV irradiation or annealing the layers, SAz releases nitrogen by forming singlet and triplet nitrenes that concurrently react with any C–H bond in the vicinity leading to sulfonamide cross-links. Condensation among trimethoxy groups in the bulk connects 4-ASPTMS units and completes the cross-linking. Simultaneously, 4-ASPTMS near the substrate reacts with surface-bound –OH motifs that anchor the cross-linked polymer chains to the substrate. We demonstrate the generation of orthogonal gradient network coatings exhibiting cross-link density (or stiffness) gradients in orthogonal directions using such a simple process. [ABSTRACT FROM AUTHOR]

An account of our development of reactions to construct N -heterocycles by triggering cyclization–migration tandem reactions from aryl azides, nitroarenes, and aryl amines is described. The reactivity patterns of metal N -aryl nitrenes, nitrosoarenes, N -aryl nitrogen radical anions, and N -aryl nitrenoids are compared. 1 Introduction 2 Unlocking the Reactivity Embedded in Aryl Azides 3 Exploiting the Reactivity of Nitrosoarenes Generated from Nitroarenes 4 Radical Anion N -Aryl Nitrogen Reactive Intermediates from Nitroarenes 5 Oxidation of Aryl Amines to Access Electrophilic N -Aryl Nitrenoids 6 Conclusion [ABSTRACT FROM AUTHOR]

Bis(pyrazolyl)borate complexes [BBN(pzR)2]Cu(I) were evaluated as catalysts in the reaction of carbene/nitrene transfer and addition to C=C bonds of a wide range of aromatic, heterocyclic and aliphatic olefins. The complexes exhibit high catalytic efficiency and selectivity in both processes. [ABSTRACT FROM AUTHOR]

We simulate two recent matrix‐isolation experiments at cryogenic temperatures, in which a nitrene undergoes spin crossover from its triplet state to a singlet state via quantum tunnelling. We detail the failure of the commonly applied weak‐coupling method (based on a linear approximation of the potentials) in describing these deep‐tunnelling reactions. The more rigorous approach of semiclassical golden‐rule instanton theory in conjunction with double‐hybrid density‐functional theory and multireference perturbation theory does, however, provide rate constants and kinetic isotope effects in good agreement with experiment. In addition, these calculations locate the optimal tunnelling pathways, which provide a molecular picture of the reaction mechanism. The reactions involve substantial heavy‐atom quantum tunnelling of carbon, nitrogen and oxygen atoms, which unexpectedly even continues to play a role at room temperature. [ABSTRACT FROM AUTHOR]

The first X‐band EPR spectrum containing only non‐overlapping signals of septet pyridyl‐2,4,6‐trinitrene and triplet pyridylnitrenes is reported. This spectrum was recorded after photolysis of 2,4,6‐triazidopyridine in solid argon at 5 K. The zero‐field splitting (ZFS) parameters of this trinitrene as well as of intermediate triplet mononitrenes and quintet dinitrenes formed at early stages of the photolysis were determined using the combination of modern computer line‐shape spectral simulations and density functional theory (DFT) calculations. It was found that septet pyridyl‐2,4,6‐trinitrene has the record negative parameter DS = −0.1031 cm−1 among all known to date septet pyridyl‐2,4,6‐trinitrenes and may be of interest as a model multi‐qubit spin system for investigations of quantum computation processing. [ABSTRACT FROM AUTHOR]

Azides have been considered as one of the energy rich functional groups as they are prominent precursors for reactive species like nitrenes and nitrenium ions. Also, they were utilized in synthesis of triazoles, triazolines and triazenes. The present work reports an eco- friendly synthesis of MgO NPs by utilizing Caesalpinia Sappan seeds as a novel fuel by solution combustion method. Multiple characterization techniques encompassing FTIR, UV- visible, XRD and SEM were used to study physico-chemical properties of synthesized MgO NPs. A convenient synthesis of amino alcohol via mixed anhydride method was carried out in the first step. Further, amino alkyl azide has been synthesized under mild condition by using the green synthesized MgO nanoparticles as a catalyst along with the addition of 2-azido-1,3- dimethylimidazolinium hexafluorophosphate, a safe, stable and efficient diazo transfer reagent. Structures of newly synthesized compounds were well characterized by HRMS, Proton and C-13 analysis techniques. [ABSTRACT FROM AUTHOR]

N-functionalized aziridines, which are both useful intermediates and important synthetic targets, can be envisioned as arising from the addition of nitrenes (i.e., NR fragments) to olefinic substrates. The exceptional reactivity of most nitrenes, in particular with respect to unimolecular decomposition, prevents general application of nitrene-transfer to the synthesis of N-functionalized aziridines. Here we demonstrate N-aryl aziridine synthesis via 1) olefin aziridination with N-aminopyridinium reagents to afford N-pyridinium aziridines followed by 2) Ni-catalyzed C–N cross-coupling of the N-pyridinium aziridines with aryl boronic acids. The N-pyridinium aziridine intermediates also participate in ring-opening chemistry with a variety of nucleophiles to afford 1,2-aminofunctionalization products. Mechanistic investigations indicate aziridine cross-coupling proceeds via a noncanonical mechanism involving initial aziridine opening promoted by the bromide counterion of the Ni catalyst, C–N cross-coupling, and finally aziridine reclosure. Together, these results provide new opportunities to achieve selective incorporation of generic aryl nitrene equivalents in organic molecules. Aziridines are useful intermediates, present in important synthetic targets. Here, the authors show a strategy for the synthesis of N-aryl aziridines based on N-aminopyridinium reagents followed by Ni-catalyzed C–N cross-coupling of N-pyridinium aziridines with aryl boronic acids. [ABSTRACT FROM AUTHOR]

As versatile synthons, nitrenes have attracted great attention. Two research topics, including nitrene precursor development and nitrene‐based transformations, have been thoroughly investigated so far. Generally, different nitrene precursors under various metal catalysis have allowed for the differentiation of the reactivity of the resulting nitrene, thus enabling diverse C−H insertions, aziridinations, and sulfimidations with high reaction efficiency and reaction generality. Among the addition of nitrenes with unsaturated bonds, the reaction of nitrenes and alkynes is still in its initial stage, although various metal‐catalyzed transformations, typically, rhodium‐catalyzed sulfinamate‐derived nitrene/alkyne metalation, have been well‐developed. Two types of plausible mechanism, radical and electrophilic models, have been proposed. The simple preparation of acyl nitrenes and their enantioselective reaction with alkynes, as well as their applications in biologically interesting architectures, is of great interest. In this review, we would like to describe the reaction of nitrenes with alkynes under metal catalysis. To increase readability, this review will be presented according to mechanistic pathways and types of metal. [ABSTRACT FROM AUTHOR]

Photochemical, metal‐free nitrene transfer reactions for C−H amination, aziridination, or sulfilimination are highly desirable. Yet, photochemical sulfilimination reactions of nitrenes with sulfides are underdeveloped as singlet nitrene species would be required for a productive reaction. Herein, we describe the blue‐light‐mediated sulfilimination reaction using iminoiodinanes. We developed a protocol for a highly efficient stoichiometric reaction, which allows for the synthesis of sulfilimines in only 10 minutes reaction time. We further applied our reaction procedure towards allyl sulfides for the synthesis of sulfenamides in a sulfilimination/rearrangement cascade reaction. Moreover, we performed computational calculations and uncovered the participation of a singlet nitrene intermediate, which rapidly reacts with methyl phenyl sulfide to give the desired product. [ABSTRACT FROM AUTHOR]

The VIth International Symposium "The Chemistry of Diazo Compounds and Related Systems" (DIAZO 2021) was held at the St. Petersburg State University from 6 to 10 September 2021. At the symposium, the advances in diazo chemistry over the past decade were summed up, and promising directions for further research were discussed. The review contains brief annotations of the plenary, keynote, invited and oral presentations and includes references to the relevant works of the speakers. [ABSTRACT FROM AUTHOR]

C−H amination and amidation by catalytic nitrene transfer are well‐established and typically proceed via electrophilic attack of nitrenoid intermediates. In contrast, the insertion of (formal) terminal nitride ligands into C−H bonds is much less developed and catalytic nitrogen atom transfer remains unknown. We here report the synthesis of a formal terminal nitride complex of palladium. Photocrystallographic, magnetic, and computational characterization support the assignment as an authentic metallonitrene (Pd−N) with a diradical nitrogen ligand that is singly bonded to PdII. Despite the subvalent nitrene character, selective C−H insertion with aldehydes follows nucleophilic selectivity. Transamidation of the benzamide product is enabled by reaction with N3SiMe3. Based on these results, a photocatalytic protocol for aldehyde C−H trimethylsilylamidation was developed that exhibits inverted, nucleophilic selectivity as compared to typical nitrene transfer catalysis. This first example of catalytic C−H nitrogen atom transfer offers facile access to primary amides after deprotection. [ABSTRACT FROM AUTHOR]

Nitrene transfer reactions represent one of the key reactions to rapidly construct new carbon-nitrogen bonds and typically require transition metal catalysts to control the reactivity of the pivotal nitrene intermediate. Herein, we report on the application of iminoiodinanes in amination reactions under visible light photochemical conditions. While a triplet nitrene can be accessed under catalyst-free conditions, the use of a suitable photosensitizer allows the access of a nitrene radical anion. Computational and mechanistic studies rationalize the access and reactivity of triplet nitrene and nitrene radical anion and allow the direct comparison of both amination reagents. We conclude with applications of both reagents in organic synthesis and showcase their reactivity in the reaction with olefins, which underline their markedly distinct reactivity. Both reagents can be accessed under mild reaction conditions at room temperature without the necessity to exclude moisture or air, which renders these metal-free, photochemical amination reactions highly practical. Gaining in-depth understanding of photochemical processes is key for developing more sustainable and efficient chemical transformations. Here the authors show that under visible light photochemical conditions, iminoiodinanes undergo formation of triplet nitrenes or nitrene radical anions, depending on the use of a photosensitizer; These reagents are studied in amination reactions with olefins. [ABSTRACT FROM AUTHOR]

The functionalisation of two-dimensional materials is key to modify their properties and facilitate assembly into functional devices. Here, new reactions have been proposed to modify crystalline two-dimensional carbon nitrides of polytriazine imide structure. Both amine alkylation and aryl-nitrene-based reactions have been explored computationally and with exploratory synthetic trials. The approach illustrates that alkylation is unfavourable, particularly at basal-plane sites. In contrast, while initial trial reactions were inconclusive, the radical-addition of nitrenes is shown to be energetically favourable, with a preference for functionalising sheet edges to minimise steric effects. [ABSTRACT FROM AUTHOR]

A stereoselective amination of thioethers to access sulfilimines using N‐mesyloxycarbamates in a catalytic system composed of iron chloride (II) and a pyridine oxazoline (PyOX) ligand, has been developed. The reaction proceeds with modest to good yields and selectivities (up to 86 : 14 d.r. and 72 : 28 e.r.). Selectivity was controlled by both the structure of the chiral ligand and the amination reagent. [ABSTRACT FROM AUTHOR]

Manganese complexes supported by macrocyclic tetrapyrrole ligands represent an important platform for nitrene transfer catalysis and have been applied to both C−H amination and olefin aziridination catalysis. The reactivity of the transient high‐valent Mn nitrenoids that mediate these processes renders characterization of these species challenging. Here we report the synthesis and nitrene transfer photochemistry of a family of MnIIIN‐haloamide complexes. The S=2 N‐haloamide complexes are characterized by 1H NMR, UV‐vis, IR, high‐frequency and ‐field EPR (HFEPR) spectroscopies, and single‐crystal X‐ray diffraction. Photolysis of these complexes results in the formal transfer of a nitrene equivalent to both C−H bonds, such as the α‐C−H bonds of tetrahydrofuran, and olefinic substrates, such as styrene, to afford aminated and aziridinated products, respectively. Low‐temperature spectroscopy and analysis of kinetic isotope effects for C−H amination indicate halogen‐dependent photoreactivity: Photolysis of N‐chloroamides proceeds via initial cleavage of the Mn−N bond to generate MnII and amidyl radical intermediates; in contrast, photolysis of N‐iodoamides proceeds via N−I cleavage to generate a MnIV nitrenoid (i.e. {MnNR}7 species). These results establish N‐haloamide ligands as viable precursors in the photosynthesis of metal nitrenes and highlight the power of ligand design to provide access to reactive intermediates in group‐transfer catalysis. [ABSTRACT FROM AUTHOR]

Nitrogen‐containing heterocycles are widely found in various biologically active substrates, pharmaceuticals, natural products and organic materials. Consequently, the continuous effort has been devoted towards the development of straightforward, economical, environmentally acceptable, efficient and ingenious methods for the synthesis of various N‐containing heterocycles and their functionalizations. Arguably, one of the most prominent direct strategy is regioselective C−H bond functionalizations which provide the step and atom economical approaches in the presence of suitable coupling partners. In this context, site‐selective migratory insertion of metal carbenes/nitrenes to the desired C−H bonds has proven as a useful tool to access various functionalized nitrogen heterocycles. In this personal account, we highlight some of our contemporary development toward constructing N‐containing heterocycles and their direct functionalizations via transition metal catalysed C−H bond functionalizations based on migratory insertion of metal‐carbenes and nitrenes. [ABSTRACT FROM AUTHOR]

The reaction of a borylnitrene with carbon dioxide is studied under cryogenic matrix isolation conditions. Photogenerated CatBN (Cat=catecholato) reacts with CO2 under formation of the cycloaddition product CatBNCO2, a 3‐oxaziridinone derivative, after photoexcitation (>550 nm). The product shows Fermi resonances between the CO stretching and ring deformation modes that cause unusual 13C and 18O isotopic shifts. A computational analysis of the 3‐oxaziridinone shows this cyclic carbamate to be less strained than an α‐lactone or an α‐lactame. [ABSTRACT FROM AUTHOR]

First W-band 94 GHz EPR spectra of randomly oriented triplet, quintet, and septet nitrenes formed during the photolysis of 1,3,5-triazido-2,4,6-tribromobenzene in cryogenic matrices are reported. In comparison with conventional X-band 9 GHz electron paramagnetic resonance (EPR) spectroscopy, W-band EPR spectroscopy allows the detection and complete spectroscopic characterization of all paramagnetic species formed at different stages of the photolysis of aromatic polyazides. This type of spectroscopy is of paramount importance for experimental determination of the sign of the zero-field splitting (ZFS) parameters of high-spin molecules with large spin-orbit contribution to the ZFS, caused by the effect of heavy atoms. The study shows that triplet 1,3-diazido-2,4,6- tribromo-5-nitrenobenzene (T1) has DT = 1.369 cm-1,ET = 0.093 cm-1, and g = 2.0033, quintet 1- azido-2,4,6-tribromo-3,5-dinitrenobenzene (Q1) shows DQ = -0.306 cm-1,EQ = 0.0137 cm-1, and g = 2.0070, and septet 2,4,6-tribromo-1,3,5-trinitrenobenzene (S1) has DS = -0.203 cm-1, ES = 0, and g = 2.0073. The experimental ZFS parameters agree well with the results of density functional theory calculations at the PBE/Ahlrichs-DZ level of theory, showing that such calculations adequately describe the magnetic properties of bromine-containing high-spin nitrenes. Both experimental and theoretical data indicate that, in contrast to all known to date quintet dinitrenes, dinitrene Q1 has the negative sign of magnetic anisotropy due to the "heavy atom effect." This dinitrene along with septet trinitrene S1 possess the largest negative value of D among all known quintet and septet organic polyradicals. [ABSTRACT FROM AUTHOR]

Copper nitrenes are proposed as reactive intermediates in a number of copper mediated aziridination and amination reactions. However, the isolation and characterization of such intermediates have proved challenging because of their transient nature. One successful approach for the stabilization of the copper-nitrene cores is the employment of a redox innocent Lewis acid (LA) like Sc3+. We herein report the stabilization of two transient copper nitrene species 3 and 4 in the absence of LAs by employing electronegative -- CF3 and -- NO2 groups in the nitrene substituent. Detailed investigations of the spectroscopic properties of 3 and 4 by theoretical and experimental methods, and a comparison of their reactivities in presence and absence of LAs provide some vital insights into the effect of LAs on the geometric and electronic structures of the copper nitrenes. [ABSTRACT FROM AUTHOR]

The photoreactivity of a series of hitherto unknown, multiply fluorinated 2‐azidobenzimidazole derivatives was investigated. The synthesis of the starting material includes regioselective p‐defluorination of nitrobenzene derivatives employing Ogoshi's conditions. If the 6‐position was unsubstituted, irradiation in the presence of N‐protected amino acids at 300 nm (Rayonet) led to the formation of arylesters by oxygenation of the 6‐position in good to excellent yields and perfect regioselectivity. We did not observe any displacement of fluoride. If the 6‐position itself was fluorinated, alternative positions of the benzene portion were attacked. Mechanistically, the reaction proceeds through ring opening of the singlet nitrene to the cyanodiimine or via the iminobenzimidazolium ion. The availability of a set of fluorinated photo‐adducts prompted the quantum chemical calculation of their 19F NMR chemical shifts. Even with the most suitable method investigated (ωB97XD/TApr‐cc‐pVDZ), deviations of up to 5 ppm from the experimental values were observed, underlining the importance of experimental measurements. [ABSTRACT FROM AUTHOR]

Copper nitrene complexes are highly reactive species and are known as intermediates in the copper catalyzed C–H amination. In this study, three novel copper tosyl nitrene complexes were synthesized at low temperatures, stabilized with heteroscorpionate ligands of the bis(pyrazolyl)methane family. The copper nitrenes were obtained by the reaction of a copper(I) acetonitrile complex with SPhINTs in dichloromethane. We show that the ligand design has a major influence on the catalytic activity and the thermal stability of the copper nitrene complex. Not only the choice of the third N donor, but also the substituent in the 5-position of the pyrazolyl moiety, have an impact on the stability. Furthermore, the novel copper nitrene complexes were used for catalytic aziridination of styrenes and C–H amination reactions of aromatic and aliphatic substrates under mild reaction conditions. Even challenging substrates like benzene and cyclohexane were aminated with good yields. The copper nitrene complexes were characterized using UV/Vis spectroscopy, low temperature Evans NMR spectroscopy, density functional theory, domain-based local pair natural orbital coupled cluster calculations (DLPNO-CCSD(T)) and cryo-UHR mass spectrometry. [ABSTRACT FROM AUTHOR]

Pristine graphene is fairly inert chemically, and as such, most application‐driven studies use graphene oxide, or reduced graphene oxide. Using substrates to modulate the reactivity of graphene represents a unique strategy in the covalent functionalization of this otherwise fairly inert material. It was found that the reactivity of pristine graphene towards perfluorophenyl azide (PFPA) can be enhanced by a metal substrate on which graphene is supported. Results on the extent of functionalization, defect density, and reaction kinetics all show that graphene supported on Ni (G/Ni) has the highest reactivity toward PFPA, followed by G/Cu and then G/silicon wafer. DFT calculations suggest that the metal substrate stabilizes the physisorbed nitrene through enhanced electron transfer to the singlet nitrene from the graphene surface assisted by the electron rich metal substrate. The G/Ni substantially stabilizes the singlet nitrene relative to G/Cu and the free‐standing graphene. The product structure is also predicted to be substrate dependent. These findings open up opportunities to enhance the reactivity of pristine graphene simply through the selection of the substrate. This also represents a new and powerful approach to increasing the reactivity of singlet nitrenes through direct electronic communication with graphene. [ABSTRACT FROM AUTHOR]

• Establishing a complete mechanism for Rh-catalyzed hydroamidation of unactivated alkenes with methyl dioxazolone. • Investigating into chemoselectivity: hydroamidation vs. C C bond aziridination and hydroamidation vs. C(sp2/sp3) H bond amidations. • The preference of singlet and triplet C H bond insertions have been clarified. • Unravelling the origins of high chemoselectivity toward hydroamidation. Rh-catalyzed hydroamidation of unactivated alkenes were investigated by a density functional theory study. The catalytic cycle proceeds through β-H elimination, alkene addition, CO 2 extrusion, nitrene migratory insertion and protodemetalation. CO 2 extrusion is the rate-determining step for the overall reaction. More importantly, the hydroamidation-to-aziridination and hydroamidation-to-amidation chemoselectivities have been investigated and the origins of impossibilities of C C bond aziridination and C(sp2/sp3) H bond amidations have been elucidated. The Rh-nitrene group is more inclined to insert Rh C bond rather than C C and C(sp2/sp3) H bonds to form the new C N bond of hydroamidation products. These calculation results provide valuable information for further selective synthesis of amides. The hydroamidation-to-aziridination and hydroamidation-to-amidation chemoselectivities have been investigated, and the origins of these high chemoselectivities have been elucidated. [Display omitted] [ABSTRACT FROM AUTHOR]

Surface functionalization of two‐dimensional crystals is a key path to tuning their intrinsic physical and chemical properties. However, synthetic protocols and experimental strategies to directly probe chemical bonding in modified surfaces are scarce. Introduced herein is a mild, surface‐specific protocol for the surface functionalization of few‐layer black phosphorus nanosheets using a family of photolytically generated nitrenes (RN) from the corresponding azides. By embedding spectroscopic tags in the organic backbone, a multitude of characterization techniques are employed to investigate in detail the chemical structure of the modified nanosheets, including vibrational, X‐ray photoelectron, solid state 31P NMR, and UV‐vis spectroscopy. To directly probe the functional groups introduced on the surface, R fragments were selected such that in conjunction with vibrational spectroscopy, 15N‐labeling experiments, and DFT methods, diagnostic P=N vibrational modes indicative of iminophosphorane units on the nanosheet surface could be conclusively identified. [ABSTRACT FROM AUTHOR]

A set of new guaianolide derivatives (1–9) was obtained from ludartin, achalensolide, and 11,13‐dihydroachalensolide by application of catalytic nitrene transfer reactions. Intermolecular nitrene C(sp3)−H insertions led to the amination of C‐1, C‐2, and C‐10 positions, while alkene aziridination was also observed under these reaction conditions. The antiproliferative activity of natural compounds and their derivatives was evaluated against a panel of human solid tumor cell lines. The results show that an increase in the biological activity was observed following amination at the C‐2 position of Ludartin, thereby demonstrating the interest in late‐stage C−H amination to improve the bioactivity of natural products. [ABSTRACT FROM AUTHOR]

Among all C‐, N‐, and O‐centered polyradicals, high‐spin nitrenes possess the largest magnetic anisotropy and are of considerable interest as multi‐level molecular spin systems for exploration of organic molecular magnetism and quantum information processing. Although the first representatives of quintet and septet nitrenes were obtained almost 50 years ago, the experimental and theoretical studies of these highly reactive species became possible only recently, owing to new achievements in molecular spectroscopy and computational chemistry. Meanwhile, dozens of various quintet dinitrenes and septet trinitrenes were successfully characterized by IR, UV/Vis, and EPR spectroscopy, thus providing important information about the electronic structure, magnetic properties and reactivity of these compounds. [ABSTRACT FROM AUTHOR]

N-heterocycles are key building blocks for many pharmaceutical products. An efficient and sustainable method for the synthesis of this class of compounds consists of the recently established intramolecular C-H amination reaction. Development of new iron-based catalysts for this transformation is of paramount importance. Herein, three major challenges in this field are addressed: the accessibility of the catalyst, the lack of mechanisticunderstanding, and the limited activity and robustness of the catalyst. These challenges are tackled by threedifferent catalysts. The first catalyst is the commercially available FeI2, that shows good activities, but is limitedto substrates with activated C-H bonds. The Fe(HMDS)2 catalyst is used to perfom in-depth mechanistic studies, revealing key intermediates of the C-H amination reaction. The third catalyst, featuring mesoionic carbene ligands, displays unprecedented activities and aminates various C-H bonds., (Copyright 2024 Wowa Stroek, Martin Albrecht. License: This work is licensed under a Creative Commons Attribution 4.0 International License.)

1,3‐Dipoles are commonly used in [3+2] cycloadditions, whereas isoelectronic uncharged dipole variants remain underdeveloped. In contrast to conventional 1,3‐dipoles, uncharged dipole equivalents form zwitterionic cycloadducts, which can be exploited to build further molecular complexity. In this work, the first cycloadditions of oxygen‐substituted isocyanates (O‐isocyanates) were studied experimentally and by DFT calculations. This unique cycloaddition strategy provides access to a novel class of heterocycle aza‐oxonium ylides through intramolecular and intermolecular cycloadditions with alkenes. This allowed a systematic study of the reactivity of the transient aza‐oxonium ylide intermediate, which can undergo N−O bond cleavage followed by nitrene C−H insertion, and the formation of β‐lactams or isoxazolidinones upon varying the structure of the alkene or O‐isocyanate reagents. [ABSTRACT FROM AUTHOR]