Iron-Catalyzed Reductive Coupling of Nitroarenes with Olefins: Intermediate of Iron–Nitroso Complex

Copper-Catalyzed Reductive Hydroamination of Inactive Diarylacetylenes with Nitroarenes

Reductive hydroamination of stable and readily available nitroarenes with unsaturated hydrocarbons represents practical access to amines. Herein, we report a simple Cu-catalyzed amine synthesis via the reductive hydroamination of nitroarenes with inactive diarylacetylenes. A series of diarylacetylenes are successfully transformed into secondary amines under mild conditions with good functional group tolerance.

Copper-Catalyzed Reductive Hydroamination of Alkenes and 1,3-Dienes with Nitroarenes

In this study, copper-catalyzed reductive hydroamination of alkenes and 1,3-dienes with nitroarenes was developed. Such umpolung hydroamination of unsaturated C═C double bonds exhibited Markovnikov selectivity, and the hydroamination of 1,3-dienes preferred 1,2-addition. Mechanistic studies suggested the system proceeds through a radical pathway with the concomitant activation of both substrates to nucleophilic alkyl radical species and electrophilic nitro-based intermediates, respectively. The attack of alkyl radical species on the N atom of nitro-based intermediates yielded the desired amines. However, this C-N cross-coupling strongly competed with the self-reduction of each species under such a system.

Cathodic Deoxygenative Alkylation of Nitro(hetero)arenes with Organic Halides

We have realized a cathodic deoxygenative alkylation between nitro(hetero)arenes and organic halides, employing bis(pinacolato)diboron (B2pin2) and LiCl as additives to trap and stabilize the generated alkyl radicals and carbanions, thereby facilitating efficient N-O cleavage and selective C-N bond formation. The protocol offers an economical method for the efficient synthesis of multiple aromatic(hetero) amines, without the need for reactive reductants and the exclusion of air and moisture. Notably, the protocol is distinguished by scalability, broad functional group compatibility, and safe and mild conditions, demonstrating practicality in the synthesis and late-stage modification of various bioactive compounds.

Recent advances in the synthetic applications of nitrosoarene chemistry

Nitroso groups are widely present in biologically active compounds in medicinal chemistry, and nitroso compounds serve as important building blocks in organic chemistry and materials science. Nitrosoarenes, in particular, showcase remarkable versatility, functioning as both electrophilic and nucleophilic reagents in a broad spectrum of organic reactions, thereby holding significant relevance in organic chemistry. This review aims to provide a comprehensive overview of the latest advancements in nitrosoarene reactions spanning a decade. Special attention is given to the synthesis of products derived from nitrosoarenes and the conditions that promote these reactions, as well as the type of catalysts. The exploration covers various facets of nitrosoarene chemistry, including cyclization, reactions involving attacks at the oxygen or nitrogen terminus, dimerization, rearrangement, coordination, and other significant reactions. By delving into these diverse reaction pathways and mechanisms, this review aspires to serve as a valuable resource for researchers seeking to deepen their understanding of nitrosoarene chemistry and its applications in both fundamental and applied scientific research.

Visible-light-induced aerobic oxidative cyclization of nitroarenes with triethylamine using an organophotocatalyst

Isoxazolidines are structurally important scaffolds in many natural products and bioactive compounds. Herein, we report a novel synthetic method for isoxazolidine derivatives through visible-light-induced photoredox cascade cyclization of nitroarenes with triethylamine under aerobic conditions. The resultant 5-hydroxyl isoxazolidine compounds were generally obtained in moderate yields with a broad range of compatible functionalities.

Photoinduced Bartoli Indole Synthesis by the Oxidative Cleavage of Alkenes with Nitro(hetero)arenes

Given the unique charm of dipole chemistry, intercepting N-O=C dipoles precisely generated by designed processes to develop novel reactivity has become a seminal challenge. The polar fragmentation of 1,3,2-dioxazolidine species generated through the radical addition of excited nitro(hetero)arenes to alkenes represents a significantly underappreciated mechanism for generating N-O=C dipoles. Herein, we present a photoinduced Bartoli indole synthesis by the oxidative cleavage of alkenes with nitro(hetero)arenes. Various indoles and azaindoles are constructed through the multi-step spontaneous rearrangement of carbonyl imine intermediates generated by the polar fragmentation of 1,3,2-dioxazolidine species. Mechanism studies and DFT calculations support that the reaction involves radical cycloaddition, ozonolysis-type cycloreversion, intramolecular H-shift of carbonyl imines, and 3,3-sigmatropic shift of O-Alkenyl hydroxylamines, etc. The implementation of continuous- flow photochemistry, in particular, significantly enhances efficiency, thereby overcoming obstacles to the commercialization process.

Deoxygenative Reduction of 1°, 2° and 3° Amides via In Situ Generated Tungsten Cluster Acting as H-Bonding Donor

A protocol of amide-to-amine transformation that is convenient, mild, and easy to perform is a long-sought goal from the viewpoint of catalysis. Herein, we have utilized easily accessible W(CO)4(NCMe)2 as a precatalyst for the deoxygenative reduction of 1°, 2° and 3° amides under mild conditions. Mechanism studies unraveled that the in situ generated W4-cluster is potentially a vital species in activating C═O of amides by providing the H-bonding network during the catalytic cycle. Significantly, this tactic offers a complementary pattern to conventional metal-catalyzed amide deoxygenative reactions with activation of the C═O bond via direct coordination with amide.

N-H Insertion of Anilines on N-Tosylhydrazones Induced by Visible Light Irradiation

Diazo compounds and their precursors represent an interesting chemical category for organic synthesis. Particularly, N-tosylhydrazones have attracted attention for their easy accessibility and diverse reactivity, including carbene transfer reactions. We described a visible light-induced N-H insertion reaction of anilines on in situ-generated diazo compounds. Optimal conditions using DBU in toluene efficiently yielded the desired products. Mechanistic studies enabled us to trap a carbene intermediate that plays a key role in the transformation.

Synthetic and Mechanistic Studies into the Reductive Functionalization of Nitro Compounds Catalyzed by an Iron(salen) Complex

We report on the use of a simple, bench-stable [Fe(salen)2]-μ-oxo precatalyst in the reduction of nitro compounds. The reaction proceeds at room temperature across a range of substrates, including nitro aromatics and aliphatics. By changing the reducing agent from pinacol borane (HBpin) to phenyl silane (H3SiPh), we can chemoselectively reduce nitro compounds while retaining carbonyl functionality. Our mechanistic studies, which include kinetics, electron paramagnetic resonance (EPR), mass spectrometry, and quantum chemistry, indicate the presence of a nitroso intermediate and the generation of an on-cycle iron hydride as a key catalytic intermediate. Based on this mechanistic insight, we were able to extend the chemistry to hydroamination and identified a simple substrate feature (alkene lowest unoccupied molecular orbital (LUMO) energy) that could be used to predict which alkenes would result in productive catalysis.

Stepwise Reduction of Redox Noninnocent Nitrosobenzene to Aniline via a Rare Phenylhydroxylamino Intermediate on a Thiolate-Bridged Dicobalt Scaffold

Nitrosobenzene (PhNO) and phenylhydroxylamine (PhNHOH) are of paramount importance because of their involvement as crucial intermediates in the biological metabolism and catalytic transformation of nitrobenzene (PhNO2) to aniline (PhNH2). However, a complete reductive transformation cycle of PhNO to PhNH2 via the PhNHOH intermediate has not been reported yet. In this context, we design and construct a new thiolate-bridged dicobalt scaffold that can accomplish coordination activation and reductive transformation of PhNO. Notably, an unprecedented reversible ligand-based redox sequence PhNO0 ↔ PhNO•- ↔ PhNO2- can be achieved on this well-defined {CoIII(μ-SPh)2CoIII} functional platform. Further detailed reactivity investigations demonstrate that the PhNO0 and PhNO•- complexes cannot react with the usual hydrogen and hydride donors to afford the corresponding phenylhydroxylamino (PhNHO-) species. However, the double reduced PhNO2- complex can readily undergo N-protonation with an uncommon weak proton donor PhSH to selectively yield a stable dicobalt PhNHO- bridged complex with a high pKa value of 13-16. Cyclic voltammetry shows that there are two successive reduction events at E1/2 = -0.075 V and Ep = -1.08 V for the PhNO0 complex, which allows us to determine both bond dissociation energy (BDEN-H) of 59-63 kcal·mol-1 and thermodynamic hydricity (ΔGH-) of 71-75 kcal·mol-1 of the PhNHO- complex. Both values indicate that the PhNO•- complex is not a potent hydrogen abstractor and the PhNO0 complex is not an efficient hydride acceptor. In the presence of BH3 as a combination of protons and electrons, facile N-O bond cleavage of the coordinated PhNHO- group can be realized to generate PhNH2 and a dicobalt hydroxide-bridged complex. Overall, we present the first stepwise reductive sequence, PhNO0 ↔ PhNO•- ↔ PhNO2- ↔ PhNHO- → PhNH2.

Regioselective hydroamination of unactivated olefins with diazirines as a diversifiable nitrogen source

Nitrogen-containing compounds, such as amines, hydrazines, and heterocycles, play an indispensable role in medicine, agriculture, and materials. Alkylated derivatives of these compounds, especially in sterically congested environments, remain a challenge to prepare. Here we report a versatile method for the regioselective hydroamination of readily available unactivated olefins with diazirines. Over fifty examples are reported, including the protecting group-free amination of fourteen different natural products. A broad functional group tolerance includes alcohols, ketones, aldehydes, and epoxides. The proximate products of these reactions are diaziridines, which, under mild conditions, are converted to primary amines, hydrazines, and heterocycles. Five target- and diversity-oriented syntheses of pharmaceutical compounds are shown, along with the preparation of a bis-15N diazirine validated in the late-stage isotopic labeling of an RNA splicing modulator candidate. In this work, we report using diazirine (1) as an electrophilic nitrogen source in a regioselective hydroamination reaction, and the diversification of the resulting diaziridines.

Low-valent-tungsten catalysis enables hydroboration of esters and nitriles

In the research presented herein, low-valent-tungsten-catalyzed hydroboration of esters and nitriles was investigated. Aromatic and aliphatic substrates were smoothly reduced to corresponding alcohol derivatives and N,N-diborylamines in the presence of W(CO)4(NCMe)2. Valuable derivatives were conveniently accessed by introducing a further functionalization process to crude hydroboration mixtures in one pot.

Intramolecular CH-Hydrogen Bonding During the Dissociation of the Oxaphosphetane Intermediate Facilitates Z/E-Selectivity in Wittig Olefination

Herein, DFT studies corroborating experimental results revealed that the shortest intramolecular hydrogen bonding distance of cis/trans-oxaphosphetane (OPA) oxygen with the CH-hydrogen of a triphenylphosphine phenyl ring provides good evidence for the attained olefin Z/E-selectivity in Wittig olefination of the studied examples. 2-Nitrobenzaldehyde, 3-nitrobenzaldehyde, 2-nitro-3-bromobenzaldehyde, 2-nitro-5-bromobenzaldehyde and 2-nitro-5-arylbenzaldehydes provided Z-nitrostilbenes with (2-chloro-4-hydroxy-3-methoxy-5-(methoxycarbonyl)benzyl) triphenylphosphonium chloride as the major products. However, 4-nitrobenzaldehyde and 2-nitro-6-bromobenzaldehydes furnished E-nitrostilbenes as the major products in high yields. Furthermore, the DFT computed intramolecular CH1/CH2-hydrogen bond distances with Cl/NO2 of selected stilbene derivatives were in good agreement with intramolecular hydrogen bond distances measured from single-crystal X-ray diffraction measurements.

Applying green chemistry principles to iron catalysis: mild and selective domino synthesis of pyrroles from nitroarenes

An efficient and general cascade synthesis of pyrroles from nitroarenes using an acid-tolerant homogeneous iron catalyst is presented. Initial (transfer) hydrogenation using the commercially available iron-Tetraphos catalyst is followed by acid catalysed Paal-Knorr condensation. Both formic acid and molecular hydrogen can be used as green reductants in this process. Particularly, under transfer hydrogenation conditions, the homogeneous catalyst shows remarkable reactivity at low temperatures, high functional group tolerance and excellent chemoselectivity transforming a wide variety of substrates. Compared to classical heterogeneous catalysts, this system presents complementing reactivity, showing none of the typical side reactions such as dehalogenation, debenzylation, arene or olefin hydrogenation. It thereby enhances the chemical toolbox in terms of orthogonal reactivity. The methodology was successfully applied to the late-stage modification of multi-functional drug(-like) molecules as well as to the one-pot synthesis of the bioactive agent BM-635.

N-Heterocyclic carbene-catalyzed enantioselective annulation of 2-amino-1H-indoles and bromoenals for the synthesis of chiral 2-aryl-2,3-dihydropyrimido[1,2-a]indol-4 (1H)-ones

An efficient N-heterocyclic carbene (NHC)-catalyzed enantioselective [3 + 3] annulation of 2-bromoenals with 2-amino-1H-indoles has been developed. A series of functionalized 2-aryl-2,3-dihydropyrimido[1,2-a]indol-4(1H)-ones were synthesized using NHCs as the catalyst in good yields with high to excellent enantioselectivities.

P(III)-Promoted Reductive Coupling of Aromatic and Aliphatic Nitro Compounds with Grignard Reagents

A phosphine-promoted reductive coupling of nitro compounds with Grignard reagents is described. Polyfunctional and pharmaceutically relevant diarylamines were generated by this reaction in moderate to high yields. Aliphatic nitro compounds that are highly challenging substrates undergo a combination of α-arylation and reductive coupling to afford the α-arylated arylamines efficiently. A series of valuable biaryl compounds with polyfluorinated and heteroaryl rings are co-generated in 56-94% yields.

Formic Acid as Carbon Monoxide Source in the Palladium-Catalyzed N-Heterocyclization of o-Nitrostyrenes to Indoles

The reductive cyclization reaction of o-nitrostyrenes to generate indoles has been investigated for three decades using CO as a cheap reducing agent, but it remains an interesting area of research and improvements. However, using toxic CO gas has several drawbacks. As a result, it is highly preferable to use safe and efficient surrogates for in situ generation of CO from nontoxic and affordable sources. Among several CO sources that have been previously explored for the generation of gaseous CO, here we report the use of cheap and readily available formic acid as an effective reductant for the reductive cyclization of o-nitrostyrenes. The reaction is air and water tolerant and provides the desired indoles in yields up to 99%, at a low catalyst loading (0.5 mol %) and without generating toxic or difficult to separate byproducts. A cheap glass thick-walled "pressure tube" can be used instead of less available autoclaves, even on a 2 g scale, thus widening the applicability of our protocol.

Nitroarenes and nitroalkenes as potential amino sources for the synthesis of N-heterocycles

Nitro-compounds are one of the cheapest and most readily available materials in the chemical industry and are commonly utilized as versatile building blocks. Previously, the synthesis of N-heterocycles was largely based on anilines. The utilization of nitroarenes and nitroalkenes for the synthesis of N-heterocyclic compounds can save at least one step, however, as compared to anilines. Thus, considerable attention has been paid to nitroarenes and nitroalkenes as new potential amino sources. Significant progress has been made in the reductive cyclization of nitroarenes or nitroalkenes to access various N-heterocycles in recent years. Herein, we comprehensively summarize the recent progress in the construction of N-heterocycles using nitroarenes and nitroalkenes as potential amino sources. The compatibility of the reaction substrate, its mechanism, applications, advantages, and limitations in this field are also discussed in detail.

Low-Valent Tungsten-Catalyzed Controllable Oxidative Dehydrogenative Coupling of Anilines

Herein, we have developed an efficient tungsten-catalyzed homogeneous system for oxidative dehydrogenative coupling of anilines to selectively produce various azoaromatics and azoxyaromatics as well as 2-substituted indolone N-oxides by simply regulating the reaction solvent with peroxide as a terminal oxidant under additive-free conditions. These findings provide an experimental framework for exploring tungsten catalysis in organic synthesis and offer an efficient and convenient tactic for the selective oxidation of anilines.

NiH-catalyzed anti-Markovnikov hydroamidation of unactivated alkenes with 1,4,2-dioxazol-5-ones for the direct synthesis of N-alkyl amides

The addition of a nitrogen-based functional group to alkenes via a direct catalytic method is an attractive way of synthesizing value-added amides. The regioselective hydroamidation of unactivated alkenes is considered one of the easiest ways to achieve this goal. Herein, we report the NiH-catalyzed anti-Markovnikov intermolecular hydroamidation of unactivated alkenes enabled by using 2,9-dibutylphenathroline (diBuphen) as the ligand. This protocol provides a platform for the direct synthesis of over 90 structurally diverse N-alkyl amides using dioxazolones, which can be easily derived from abundant carboxylic acid feedstocks. This method succeeds for both terminal and internal unactivated alkenes and some natural products. Mechanistic studies including DFT calculations reveal an initial reversible insertion/elimination of the [NiH] to the alkene, followed by the irreversible amidation to furnish the N-alkyl amides. By crossover experiments and deuterium labeling studies, the observed anti-Markovnikov regioselectivities are suggested to be controlled by the sterical environment of the coupling reaction.

Annulation strategies for diverse heterocycles via the reductive transformation of 2-nitrostyrenes

Reduction of the stable nitro group is a fundamental and widely used transformation for the construction of complex and functionalized heterocyclic architectures. The unfolding of the reactivity of the nitro group in the 2-nitrostyrene moiety not only triggers the formation of carbon-nitrogen bonds, but also offers the opportunity for annulation and heteroannulation, thereby providing a cascade process for the synthesis of highly conjugated natural and unnatural molecules. In this review, we comprehensively discuss the use of 2-nitrostyrene motifs in the synthesis of various N-heterocycles. We offer readers an overview of the synthetic achievements achieved to date, highlighting their important features, reactivities, and mechanisms.

Bioinspired Iron-Catalyzed Dehydration of Aldoximes to Nitriles: A General N-O Redox-Cleavage Method

Inspired by OxdA that operates biocatalytic aldoxime dehydration, we have developed an efficient iron catalyst, Cp*Fe(1,2-Cy₂PC₆H₄O) (1), which rapidly converts various aliphatic and aromatic aldoximes to nitriles with release of H₂O at room temperature. The catalysis involves redox activation of the N-O bond by a 1e^- transfer from the iron catalyst to the oxime. Such redox-mediated N-O cleavage was demonstrated by the isolation of a ferrous iminato intermediate from the reaction of the ketoxime substrate. This iron-catalyzed acceptorless dehydration approach represents a general method for the preparation of nitriles, and it also delivers salicylonitriles by catalyzing the Kemp elimination reaction.

Palladium-Catalyzed Intramolecular Heck/Aminocarbonylation of Alkene-Tethered Iodobenzenes with Nitro Compounds: Synthesis of Carbamoyl-Substituted Benzoheterocycles

A palladium-catalyzed intramolecular Heck/aminocarbonylation of alkene-tethered iodobenzenes with nitro compounds has been developed for the synthesis of carbamoyl-substituted benzoheterocycles. Using Mo(CO)₆ as a solid CO source, no external reductant or additives were needed in this procedure. Both nitroarenes and nitroalkanes were well tolerated. A range of carbamoyl-substituted dihydrobenzofurans and indolines were prepared in moderate to high yields.

Decarboxylative tandem C-N coupling with nitroarenes via SH2 mechanism

Aromatic tertiary amines are one of the most important classes of organic compounds in organic chemistry and drug discovery. It is difficult to efficiently construct tertiary amines from primary amines via classical nucleophilic substitution due to consecutive overalkylation. In this paper, we have developed a radical tandem C-N coupling strategy to efficiently construct aromatic tertiary amines from commercially available carboxylic acids and nitroarenes. A variety of aromatic tertiary amines can be furnished in good yields (up to 98%) with excellent functional group compatibility under mild reaction conditions. The use of two different carboxylic acids also allows for the concise synthesis of nonsymmetric aromatic tertiary amines in satisfactory yields. Mechanistic studies suggest the intermediacy of the arylamine–(TPP)Fe(III) species and might provide a possible evidence for an S_H2 (bimolecular homolytic substitution) pathway in the critical C-N bond formation step.

Aromatic tertiary amines are versatile building blocks in organic synthesis. In this article, the authors report on an iron-catalysed reaction for the decarboxylative C-N coupling from carboxylic acids and nitroarenes, leading to non-symmetric tertiary aromatic amines.

One-pot synthesis of 2-arylindole derivatives under transition-metal-free conditions

A new and simple method to prepare 2-arylindole derivatives under transition-metal-free conditions has been developed. When N-acetyl-2-methyl-3-nitroaniline was treated with 2-fluorobenzaldehydes in the presence of Cs2CO3 in DMF at 60 ⁰C, the desired indoles were typically obtained in moderate to good yields (up to 83%). Other aniline substrates were also employed, but only the Knoevenagel condensation occurred to give the corresponding diarylethenes in moderate to excellent yields.

Encapsulating Electron-Rich Pd NPs with Lewis Acidic MOF: Reconciling the Electron-Preference Conflict of the Catalyst for Cascade Condensation via Nitro Reduction

Cascade reactions take advantage of step-saving and facile operation for obtaining chemicals. Herein, catalytic hydrogenation of nitroarene coupled condensation with β-diketone to afford β-ketoenamines is achieved by an integrated nanocatalyst, Pd-e@UiO-66. The catalyst has the structure of an acid-rich metal-organic framework (MOF), UiO-66-encapsulated electron-rich Pd nanoparticles, and it reconciles the electron-effect contradiction of cascade catalytic reactions: catalytic hydrogenation requires an electron-rich catalyst, while condensation requires electron-deficient Lewis acid sites. The catalyst showed good activity, high chemoselectivity, and universal applicability for the synthesis of β-ketoenamines using nitroarenes. More than 30 β-ketoenamines have been successfully prepared with up to 99% yield via the methodology of relay catalysis. The catalyst exhibited excellent stability to maintain its catalytic performance for more than five cycles. Furthermore, we conducted an in-depth exploration of the reaction mechanism with theoretical calculations.

HFIP as Protonation Reagent and Solvent for Regioselective Alkylation of Indoles with All-Carbon Centers

The regio- and chemoselective construction of indole bearing an all-carbon center at the C3-position, a versatile bioactive building block, by C(sp²)-C(sp³) formation with olefins has been achieved through utilization of hexafluoroisopropanol (HFIP) as the protonation reagent and solvent. The catalytic reactions are operationally simple and green compared with previous reports utilizing elaborated olefins and catalysts. This protocol allows for alkylation of a variety of substituted indoles with diverse of styrene type alkenes in excellent yields and with high selectivity. Application of this protocol to the synthesis of drug was pursued and with an improved yield in contrast to previous art. Catalytic kinetics and deuterium-labeling experiments suggest that the rate-determining step involves the protonation of olefin by HFIP to generate carbocation, followed by electrophilic addition to indole derivative.

Copper-promoted cross-coupling of nitroarenes with 4-alkyl-1,4-dihydropyridines using a peroxide-driven radical reductive strategy

Direct radical-mediated reductive coupling of nitroarenes with 4-alkyl-1,4-dihydropyridines to build the C(sp3)–N bond using 4-alkyl-1,4-dihydropyridines as internal reducing agents and alkyl sources is presented.

Manganese-mediated reductive N,N-dialkylation of nitroarenes: a dramatic NiI2 effect

A dramatic NiI2 effect has been found for Mn-mediated reductive N,N-dialkylation of nitroaromatics.

Generation of a Sulfinamide Species from Facile N-O Bond Cleavage of Nitrosobenzene by a Thiolate-Bridged Diiron Complex

The activation of nitrosobenzene promoted by transition-metal complexes has gained considerable interest due to its significance for understanding biological processes and catalytic C-N bond formation processes. Despite intensive studies in the past decades, there are only limited cases where electron-rich metal centers were commonly employed to achieve the N-O or C-N bond cleavage of the coordinated nitrosobenzene. In this regard, it is significant and challenging to construct a suitable functional system for examining its unique reactivity toward reductive activation of nitrosoarene. Herein, we present a {Fe₂S₂} functional platform that can activate nitrosobenzene via an unprecedented iron-directed thiolate insertion into the N-O bond to selectively generate a well-defined diiron benzenesulfinamide complex. Furthermore, computational studies support a proposal that in this concerted four-electron reduction process of nitrosobenzene the iron center serves as an important electron shuttle. Notably, compared to the intact bridging nitrosoarene ligand, the benzenesulfinamide moiety has priority to convert into aniline in the presence of separate or combined protons and reductants, which may imply the formation of the sulfinamide species accelerates reduction process of nitrosoarene. The reaction pattern presented here represents a novel activation mode of nitrosobenzene realized by a thiolate-bridged diiron complex.

Reductive C-N Coupling of Nitroarenes: Heterogenization of MoO3 Catalyst by Confinement in Silica

The construction of C-N bonds with nitroaromatics and boronic acids using highly efficient and recyclable catalysts remains a challenge. In this study, nanoporous MoO₃ confined in silica serves as an efficient heterogeneous catalyst for C-N cross-coupling of nitroaromatics with aryl or alkyl boronic acids to deliver N-arylamines and with desirable multiple reusability. Experimental results suggest that silica not only heterogenizes the Mo species in the confined mesoporous microenvironment but also significantly reduces the reaction induction period and regulates the chemical efficiency of the targeted product. The well-shaped MoO₃ @m-SiO₂ catalyst exhibits improved catalytic performance both in yield and turnover number, in contrast with homogeneous Mo catalysts, commercial Pd/C, or MoO₃ nanoparticles. This approach offers a new avenue for the heterogeneous catalytic synthesis of valuable bioactive molecules.

Site-specific Umpolung amidation of carboxylic acids via triplet synergistic catalysis

Development of catalytic amide bond-forming methods is important because they could potentially address the existing limitations of classical methods using superstoichiometric activating reagents. In this paper, we disclose an Umpolung amidation reaction of carboxylic acids with nitroarenes and nitroalkanes enabled by the triplet synergistic catalysis of FeI₂, P(V)/P(III) and photoredox catalysis, which avoids the production of byproducts from stoichiometric coupling reagents. A wide range of carboxylic acids, including aliphatic, aromatic and alkenyl acids participate smoothly in such reactions, generating structurally diverse amides in good yields (86 examples, up to 97% yield). This Umpolung amidation strategy opens a method to address challenging regioselectivity issues between nucleophilic functional groups, and complements the functional group compatibility of the classical amidation protocols. The synthetic robustness of the reaction is demonstrated by late-stage modification of complex molecules and gram-scale applications.

Catalytic amide bond-forming methods is important because they could potentially address the existing limitations of classical methods using superstoichiometric activating reagents. Here the authors show an Umpolung amidation reaction of carboxylic acids with nitroarenes and nitroalkanes enabled by FeI₂, P(V)/P(III) and photoredox catalysis that avoids the production of byproducts.

NaI/PPh3-Mediated Photochemical Reduction and Amination of Nitroarenes

A mild transition-metal- and photosensitizer-free photoredox system based on the combination of NaI and PPh₃ was found to enable highly selective reduction of nitroarenes. This protocol tolerates a broad range of reducible functional groups such as halogen (Cl, Br, and even I), aldehyde, ketone, carboxyl, and cyano. Moreover, the photoredox catalysis with NaI and stoichiometric PPh₃ provides also an alternative entry to Cadogan-type reductive amination when o-nitrobiarenes were used.

Earth-Abundant 3d Transition Metal Catalysts for Hydroalkoxylation and Hydroamination of Unactivated Alkenes

This review summarizes the most noteworthy achievements in the field of C–O and C–N bond formation by hydroalkoxylation and hydroamination reactions on unactivated alkenes (including 1,2- and 1,3-dienes) promoted by earth-abundant 3d transition metal catalysts based on manganese, iron, cobalt, nickel, copper and zinc. The relevant literature from 2012 until early 2021 has been covered.

Iron-catalyzed hydrogen atom transfer induced cyclization of 1,6-enynes for the synthesis of ketoximes: a combined experimental and computational study

An iron-catalyzed reductive radical cyclization/hydro-oximation of 1,6-enynes with tBuONO was developed, leading to functionalized benzofuran, benzothiophene, and cyclopentenyl-based ketoximes.

Ruthenium-catalysed chemoselective alkylation of nitroarenes with alkanols

The alkylation of nitroarenes with akanols catalysed by the phosphinesulfonate ruthenium complex was reported. It displays different reactivity and chemoselectivity depending on the acid–base conditions, delivering diverse anilines from nitroarenes.