Mechanisms of organic oxidation and reduction by metal complexes

High-Valent Copper Catalysis Enables Regioselective Fluoroarylation of Gem-Difluorinated Cyclopropanes

Transition-metal (TM) catalyzed reaction of gem-difluorinated cyclopropanes (gem-DFCPs) has drawn much attention recently. The reaction generally occurs via the activation of the distal C─C bond in gem-DFCPs by a low-valent TM through oxidative addition, eventually producing mono-fluoro olefins as the coupling products. However, achieving regioselective activation of the proximal C─C bond in gem-DFCPs that overcomes the intrinsic reactivity via TM catalysis remains elusive. Here, a new reaction mode of gem-DFCPs enabled by high-valent copper catalysis, which allows exclusive activation of the congested proximal C─C bond is presented. The reaction that achieves fluoroarylation of gem-DFCPs uses NFSI (N-fluorobenzenesulfonimide) as electrophilic fluoro reagent and arenes as the C─H nucleophiles, enabling the synthesis of diverse CF3-containing scaffolds. It is proposed that a high-valent copper species plays an important role in the regioselective activation of the proximal C─C bond possibly via a σ-bond metathesis.

Copper-catalysed dehydrogenation or lactonization of C(sp3)-H bonds

Cytochrome P450 enzymes are known to catalyse bimodal oxidation of aliphatic acids via radical intermediates, which partition between pathways of hydroxylation and desaturation1,2. Developing analogous catalytic systems for remote C-H functionalization remains a significant challenge3-5. Here, we report the development of Cu(I)-catalysed bimodal dehydrogenation/lactonization reactions of synthetically common N-methoxyamides through radical abstractions of the γ-aliphatic C-H bonds. The feasibility of switching from dehydrogenation to lactonization is also demonstrated by altering reaction conditions. The use of a readily available amide as both radical precursor and internal oxidant allows for the development of redox-neutral C-H functionalization reactions with methanol as the sole side product. These C-H functionalization reactions using a Cu(I) catalyst with loading as low as 0.5 mol.% is applied to the diversification of a wide range of aliphatic acids including drug molecules and natural products. The exceptional compatibility of this catalytic system with a wide range of oxidatively sensitive functionality demonstrates the unique advantage of using a simple amide substrate as a mild internal oxidant.

Cu(II) salts as terminal oxidants in visible-light photochemical oxidation reactions

Photochemistry provides an important platform for the discovery of synthetically useful transformations. The development of new oxidative photoreactions, however, has proven to be relatively challenging. The importance of the identity of the terminal oxidant has been an underappreciated consideration in the design of these reactions. Many of the most common terminal oxidants used in ground-state catalytic methods are poorly compatible with the one-electron oxidation state changes characteristic of photoredox reactions and result in hard-to-control deleterious side reactions. As an alternative, Cu(II) salts have emerged as versatile terminal oxidants in photochemical oxidation reactions that are terrestrially abundant, cost-effective, and readily compatible with one-electron oxidation state changes. This review highlights recent reaction methods that leverage Cu(II) oxidation in combination with the photochemical activation of substrates or that use Cu(II) salts as both the active chromophore and terminal oxidant.

Photocatalytic, modular difunctionalization of alkenes enabled by ligand-to-metal charge transfer and radical ligand transfer

Ligand-to-metal charge transfer (LMCT) is a mechanistic strategy that provides a powerful tool to access diverse open-shell species using earth abundant elements and has seen tremendous growth in recent years. However, among many reaction manifolds driven by LMCT reactivity, a general and catalytic protocol for modular difunctionalization of alkenes remains unknown. Leveraging the synergistic cooperation of iron-catalyzed ligand-to-metal charge transfer and radical ligand transfer (RLT), here we report a photocatalytic, modular difunctionalization of alkenes using inexpensive iron salts catalytically to function as both radical initiator and terminator. Additionally, strategic use of a fluorine atom transfer reagent allows for general fluorochlorination of alkenes, providing the first example of interhalogen compound formation using earth abundant element photocatalysis. Broad scope, mild conditions and versatility in converting orthogonal nucleophiles (TMSN3 and NaCl) directly into corresponding open-shell radical species are demonstrated in this study, providing a robust means towards accessing vicinal diazides and homo-/hetero-dihalides motifs catalytically. These functionalities are important precursors/intermediates in medicinal and material chemistry. Preliminary mechanistic studies support the radical nature of these transformations, disclosing the tandem LMCT/RLT as a powerful reaction manifold in catalytic olefin difunctionalization.

Unveiling the Reduction Mechanism of Pu(IV) by Acetaldoxime

The separation of plutonium (Pu) from spent nuclear fuel was achieved by effectively adjusting the oxidation state of Pu from +IV to +III in the plutonium uranium reduction extraction (PUREX) process. Acetaldoxime (CH3CHNOH) as a free salt reductant can rapidly reduce Pu(IV), but the reduction mechanism remains indistinct. Herein, we explore the reduction mechanism of two Pu(IV) ions by one CH3CHNOH molecule, where the second Pu(IV) reduction is the rate-determining step with the energy barrier of 19.24 kcal mol-1, which is in line with the experimental activation energy (20.95 ± 2.34 kcal mol-1). Additionally, the results of structure and spin density analyses demonstrate that the first and second Pu(IV) reduction is attributed to hydrogen atom transfer and hydroxyl ligand transfer, respectively. Analysis of localized molecular orbitals unveils that the reduction process is accompanied by the breaking of the Pu-OOH bond and the formation of the OOH-H and C-OOH bonds. The reaction energies confirm that the reduction of Pu(IV) by acetaldoxime is both thermodynamically and kinetically accessible. In this work, we elucidate the reduction mechanism of Pu(IV) with CH3CHNOH, which provides a theoretical understanding of the rapid reduction of Pu(IV).

Radical ligand transfer: a general strategy for radical functionalization

The place of alkyl radicals in organic chemistry has changed markedly over the last several decades, evolving from challenging-to-generate "uncontrollable" species prone to side reactions to versatile reactive intermediates enabling construction of myriad C-C and C-X bonds. This maturation of free radical chemistry has been enabled by several advances, including the proliferation of efficient radical generation methods, such as hydrogen atom transfer (HAT), alkene addition, and decarboxylation. At least as important has been innovation in radical functionalization methods, including radical-polar crossover (RPC), enabling these intermediates to be engaged in productive and efficient bond-forming steps. However, direct engagement of alkyl radicals remains challenging. Among these functionalization approaches, a bio-inspired mechanistic paradigm known as radical ligand transfer (RLT) has emerged as a particularly promising and versatile means of forming new bonds catalytically to alkyl radicals. This development has been driven by several key features of RLT catalysis, including the ability to form diverse bonds (including C-X, C-N, and C-S), the use of simple earth abundant element catalysts, and the intrinsic compatibility of this approach with varied radical generation methods, including HAT, radical addition, and decarboxylation. Here, we provide an overview of the evolution of RLT catalysis from initial studies to recent advances and provide a conceptual framework we hope will inspire and enable future work using this versatile elementary step.

Photo- and Metal-Mediated Deconstructive Approaches to Cyclic Aliphatic Amine Diversification

Described herein are studies toward the core modification of cyclic aliphatic amines using either a riboflavin/photo-irradiation approach or Cu(I) and Ag(I) to mediate the process. Structural remodeling of cyclic amines is explored through oxidative C-N and C-C bond cleavage using peroxydisulfate (persulfate) as an oxidant. Ring-opening reactions to access linear aldehydes or carboxylic acids with flavin-derived photocatalysis or Cu salts, respectively, are demonstrated. A complementary ring-opening process mediated by Ag(I) facilitates decarboxylative Csp³-Csp² coupling in Minisci-type reactions through a key alkyl radical intermediate. Heterocycle interconversion is demonstrated through the transformation of N-acyl cyclic amines to oxazines using Cu(II) oxidation of the alkyl radical. These transformations are investigated by computation to inform the proposed mechanistic pathways. Computational studies indicate that persulfate mediates oxidation of cyclic amines with concomitant reduction of riboflavin. Persulfate is subsequently reduced by formal hydride transfer from the reduced riboflavin catalyst. Oxidation of the cyclic aliphatic amines with a Cu(I) salt is proposed to be initiated by homolysis of the peroxy bond of persulfate followed by α-HAT from the cyclic amine and radical recombination to form an α-sulfate adduct, which is hydrolyzed to the hemiaminal. Investigation of the pathway to form oxazines indicates a kinetic preference for cyclization over more typical elimination pathways to form olefins through Cu(II) oxidation of alkyl radicals.

Copper-Catalyzed Decarboxylative Elimination of Carboxylic Acids to Styrenes

A copper-catalyzed decarboxylative elimination reaction of (hetero)aromatic propionic acids to vinyl (hetero)arenes has been developed. This method furnishes alkenes from carboxylic acids without the need for stochiometric Pb or Ag additives or expensive or specialized photocatalysts. A series of mechanistic experiments indicate that the reaction proceeds via benzylic deprotonation and subsequent radical decarboxylation; a pathway that is distinct from the single-electron-transfer mechanisms implicated in related decarboxylative elimination reactions.

Photochemical diazidation of alkenes enabled by ligand-to-metal charge transfer and radical ligand transfer

Vicinal diamines are privileged synthetic motifs in chemistry due to their prevalence and powerful applications in bioactive molecules, pharmaceuticals, and ligand design for transition metals. With organic diazides being regarded as modular precursors to vicinal diamines, enormous efforts have been devoted to developing efficient strategies to access organic diazide generated from olefins, themselves common feedstock chemicals. However, state-of-the-art methods for alkene diazidation rely on the usage of corrosive and expensive oxidants or complicated electrochemical setups, significantly limiting the substrate tolerance and practicality of these methods on large scale. Toward overcoming these limitations, here we show a photochemical diazidation of alkenes via iron-mediated ligand-to-metal charge transfer (LMCT) and radical ligand transfer (RLT). Leveraging the merger of these two reaction manifolds, we utilize a stable, earth abundant, and inexpensive iron salt to function as both radical initiator and terminator. Mild conditions, broad alkene scope and amenability to continuous-flow chemistry rendering the transformation photocatalytic were demonstrated. Preliminary mechanistic studies support the radical nature of the cooperative process in the photochemical diazidation, revealing this approach to be a powerful means of olefin difunctionalization.

Synthesis and Glycosidation of Anomeric Halides: Evolution from Early Studies to Modern Methods of the 21st Century

Advances in synthetic carbohydrate chemistry have dramatically improved access to common glycans. However, many novel methods still fail to adequately address challenges associated with chemical glycosylation and glycan synthesis. Since a challenge of glycosylation has remained, scientists have been frequently returning to the traditional glycosyl donors. This review is dedicated to glycosyl halides that have played crucial roles in shaping the field of glycosciences and continue to pave the way toward our understanding of chemical glycosylation.

Modular Difunctionalization of Unactivated Alkenes through Bio-Inspired Radical Ligand Transfer Catalysis

Development of visible light-mediated atom transfer radical addition of haloalkanes onto unsaturated hydrocarbons has seen rapid growth in recent years. However, due to its radical chain propagation mechanism, diverse functionality other than the pre-existing (pseudo-)halide on the alkyl halide source cannot be incorporated into target molecules in a one-step, economic fashion. Inspired by the prominent reactivities shown by cytochrome P450 hydroxylase and non-heme iron-dependent oxygenases, we herein report the first modular, dual catalytic difunctionalization of unactivated alkenes via manganese-catalyzed radical ligand transfer (RLT). This RLT elementary step involves a coordinated nucleophile rebounding to a carbon-centered radical to form a new C-X bond in analogy to the radical rebound step in metalloenzymes. The protocol leverages the synergetic cooperation of both a photocatalyst and earth-abundant manganese complex to deliver two radical species in succession to minimally functionalized alkenes, enabling modular diversification of the radical intermediate by a high-valent manganese species capable of delivering various external nucleophiles. A broad scope (97 examples, including drugs/natural product motifs), mild conditions, and excellent chemoselectivity were shown for a variety of substrates and fluoroalkyl fragments. Mechanistic and kinetics studies provide insights into the radical nature of the dual catalytic transformation and support radical ligand transfer (RLT) as a new strategy to deliver diverse functionality selectively to carbon-centered radicals.

Evolution towards green radical generation in total synthesis

The use of radicals as intermediates in total synthesis has evolved since their initial use in the latter half of the twentieth century. Radical generation from metal hydride methodologies has shifted to "greener" techniques including catalytic metal-mediated systems, electrochemical and photoredox-mediated processes. This review will focus on these classical and contemporary methods for radical generation and their applications in recent total syntheses.

Decarboxylative Halogenation of Organic Compounds

Decarboxylative halogenation, or halodecarboxylation, represents one of the fundamental key methods for the synthesis of ubiquitous organic halides. The method is based on conversion of carboxylic acids to the corresponding organic halides via selective cleavage of a carbon-carbon bond between the skeleton of the molecule and the carboxylic group and the liberation of carbon dioxide. In this review, we discuss and analyze major approaches for the conversion of alkanoic, alkenoic, acetylenic, and (hetero)aromatic acids to the corresponding alkyl, alkenyl, alkynyl, and (hetero)aryl halides. These methods include the preparation of families of valuable organic iodides, bromides, chlorides, and fluorides. The historic and modern methods for halodecarboxylation reactions are broadly discussed, including analysis of their advantages and drawbacks. We critically address the features, reaction selectivity, substrate scopes, and limitations of the approaches. In the available cases, mechanistic details of the reactions are presented, and the generality and uniqueness of the different mechanistic pathways are highlighted. The challenges, opportunities, and future directions in the field of decarboxylative halogenation are provided.

Iron-catalyzed remote functionalization of inert C(sp3)-H bonds of alkenes via 1,n-hydrogen-atom-transfer by C-centered radical relay

As an alternative approach to traditional C-H activation that often involved harsh conditions, and vicinal or primary C-H functionalization, radical relay offers a solution to these long-held problems. Enabled by 1,n (n = 5, 6)-hydrogen atom transfer (HAT), we use a most prevalent moiety, alkene, as the precursor to an sp³ C-centered radical to promote selective cleavage of inert C(sp³)-H bonds for the generation of azidotrifluoromethylated molecules. Mild conditions, broad scope and excellent regioselective control (>20 : 1) are observed in the reactions. Deuterium labelling studies disclose the kinetic characteristics of the transformations and verify a direct 1,n-HAT pathway. The key to this C-centered radical relay is that iron plays a dual role as a radical initiator and terminator to incorporate the azide functionality through radical oxidation via azido-ligand-transfer. The methods and the later derivatization promise expeditious synthesis of CF₃-containing organic azides, γ-lactam and triazoles that are widely used in designing new fluorescent tags and functional materials.

Diastereoselective sp3 C-O Bond Formation via Visible Light-Induced, Copper-Catalyzed Cross-Couplings of Glycosyl Bromides with Aliphatic Alcohols

Copper-catalyzed cross-coupling reactions have become one of the most powerful methods for generating carbon-heteroatom bonds, an important framework of many organic molecules. However, copper-catalyzed C(sp³)-O cross-coupling of alkyl halides with alkyl alcohols remains elusive because of the sluggish nature of oxidative addition to copper. To address this challenge, we have developed a catalytic copper system, which overcomes the copper oxidative addition barrier with the aid of visible light and effectively facilitates the cross-couplings of glycosyl bromides with aliphatic alcohols to afford C(sp³)-O bonds with high levels of diastereoselectivity. Importantly, this catalytic system leads to a mild and efficient method for stereoselective construction of α-1,2-cis glycosides, which are of paramount importance, but challenging. In general, stereochemical outcomes in α-1,2-cis glycosidic C-O bond-forming processes are unpredictable and dependent on the steric and electronic nature of protecting groups bound to carbohydrate coupling partners. Currently, the most reliable approaches rely on the use of a chiral auxiliary or hydrogen-bond directing group at the C2- and C4-position of carbohydrate electrophiles to control α-1,2-cis selectivity. In our approach, earth-abundant copper not only acts as a photocatalyst and a bond-forming catalyst, but also enforces the stereocontrolled formation of anomeric C-O bonds. This cross-coupling protocol enables highly diastereoselective access to a wide variety of α-1,2-cis-glycosides and biologically relevant α-glycan oligosaccharides. Our work provides a foundation for developing new methods for the stereoselective construction of natural and unnatural anomeric carbon(sp³)-heteroatom bonds.

C(sp3)-H Fluorination with a Copper(II)/(III) Redox Couple

Despite the growing interest in the synthesis of fluorinated organic compounds, few reactions are able to incorporate fluoride ions directly into alkyl C-H bonds. Here, we report the C(sp³)-H fluorination reactivity of a formally copper(III) fluoride complex. The C-H fluorination intermediate, LCuF, along with its chloride and bromide analogues, LCuCl and LCuBr, were prepared directly from halide sources with a chemical oxidant and fully characterized with single-crystal X-ray diffraction, X-ray absorption spectroscopy, UV-vis spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. Quantum chemical calculations reveal significant halide radical character for all complexes, suggesting their ability to initiate and terminate a C(sp³)-H halogenation sequence by sequential hydrogen atom abstraction (HAA) and radical capture. The capability of HAA by the formally copper(III) halide complexes was explored with 9,10-dihydroanthracene, revealing that LCuF exhibits rates 2 orders of magnitude higher than LCuCl and LCuBr. In contrast, all three complexes efficiently capture carbon radicals to afford C(sp³)-halogen bonds. Mechanistic investigation of radical capture with a triphenylmethyl radical revealed that LCuF proceeds through a concerted mechanism, while LCuCl and LCuBr follow a stepwise electron transfer-halide transfer pathway. The capability of LCuF to perform both hydrogen atom abstraction and radical capture was leveraged to enable fluorination of allylic and benzylic C-H bonds and α-C-H bonds of ethers at room temperature.

Remote azidation of C(sp3)–H bonds to synthesize δ-azido sulfonamidesviairon-catalyzed radical relay

A selective remote C–H azidation was developed with an iron catalyst playing dual roles as a radical initiator and terminator.

Decarboxylative Acetoxylation of Aliphatic Carboxylic Acids

Organic molecules bearing acetoxy moieties are important functionalities in natural products, drugs, and agricultural chemicals. Synthesis of such molecules via transition metal-catalyzed C-O bond formation can be achieved in the presence of a carefully chosen directing group to alleviate the challenges associated with regioselectivity. An alternative approach is to use ubiquitous carboxylic acids as starting materials and perform a decarboxylative coupling. Herein, we report conditions for a photocatalytic decarboxylative C-O bond formation reaction that provides rapid and facile access to the corresponding acetoxylated products. Mechanistic investigations suggest that the reaction operates via oxidation of the carboxylate followed by rapid decarboxylation and oxidation by Cu(OAc)₂.

Reaction of Nitrogen-Radicals with Organometallics Under Ni-Catalysis: N-Arylations and Amino-Functionalization Cascades

Herein, we report a strategy for the generation of nitrogen-radicals by ground-state single electron transfer with organyl-NiI species. Depending on the philicity of the N-radical, two types of processes have been developed. In the case of nucleophilic aminyl radicals direct N-arylation with aryl organozinc, organoboron, and organosilicon reagents was achieved. In the case of electrophilic amidyl radicals, cascade processes involving intramolecular cyclization, followed by reaction with both aryl and alkyl organometallics have been developed. The N-cyclization-alkylation cascade introduces a novel retrosynthetic disconnection for the assembly of substituted lactams and pyrrolidines with its potential demonstrated in the short total synthesis of four venom alkaloids.

Photoinduced Kochi Decarboxylative Elimination for the Synthesis of Enamides and Enecarbamates from N-Acyl Amino Acids

Decarboxylative elimination of easily accessible N-acyl amino acids to provide enamide and enecarbamate building blocks has been realized through the combination of an organophotoredox catalyst and copper acetate as the terminal oxidant. This operationally simple process utilizes inexpensive and readily available reagents without preactivation of the carboxylic acid. Enamides and enecarbamates are now accessible directly from N-acyl amino acids consequently improving upon the utility of Kochi's oxidative decarboxylation of carboxylic acids.

Iron-Catalyzed Direct Olefin Diazidation via Peroxyester Activation Promoted by Nitrogen-Based Ligands

We herein report an iron-catalyzed direct diazidation method via activation of bench-stable peroxyesters promoted by nitrogen-based ligands. This method is effective for a broad range of olefins and N-heterocycles, including those that are difficult substrates for the existing olefin diamination and diazidation methods. Notably, nearly a stoichiometric amount of oxidant and TMSN₃ are sufficient for high-yielding diazidation for most substrates. Preliminary mechanistic studies elucidated the similarities and differences between this method and the benziodoxole-based olefin diazidation method previously developed by us. This method effectively addresses the limitations of the existing olefin diazidation methods. Most notably, previously problematic nonproductive oxidant decomposition can be minimized. Furthermore, X-ray crystallographic studies suggest that an iron-azide-ligand complex can be generated in situ from an iron acetate precatalyst and that it may facilitate peroxyester activation and the rate-determining C-N₃ bond formation during diazidation of unstrained olefins.

Process Safety Assessment of the Iron-Catalyzed Direct Olefin Diazidation for the Expedient Synthesis of Vicinal Primary Diamines

We report herein a process safety assessment of the iron-catalyzed direct olefin diazidation for the preparation of a broad range of synthetically valuable vicinal primary diamines. Differential scanning calorimetry analysis of the corresponding reagents, intermediates, and a list of representative diazide/diaminium salt products revealed that all of them are thermal stable at the reaction temperature. The drop weight test of the diazides suggested that they are moderately impact-sensitive. Guided by this assessment, an optimized olefin diazidation/diamination procedure has been developed which allows for the gram-scale diaminium salt synthesis without purification of the diazide intermediate.

Beyond ferryl-mediated hydroxylation: 40 years of the rebound mechanism and C-H activation

Since our initial report in 1976, the oxygen rebound mechanism has become the consensus mechanistic feature for an expanding variety of enzymatic C-H functionalization reactions and small molecule biomimetic catalysts. For both the biotransformations and models, an initial hydrogen atom abstraction from the substrate (R-H) by high-valent iron-oxo species (Feⁿ=O) generates a substrate radical and a reduced iron hydroxide, [Fe^n-1-OH ·R]. This caged radical pair then evolves on a complicated energy landscape through a number of reaction pathways, such as oxygen rebound to form R-OH, rebound to a non-oxygen atom affording R-X, electron transfer of the incipient radical to yield a carbocation, R⁺, desaturation to form olefins, and radical cage escape. These various flavors of the rebound process, often in competition with each other, give rise to the wide range of C-H functionalization reactions performed by iron-containing oxygenases. In this review, we first recount the history of radical rebound mechanisms, their general features, and key intermediates involved. We will discuss in detail the factors that affect the behavior of the initial caged radical pair and the lifetimes of the incipient substrate radicals. Several representative examples of enzymatic C-H transformations are selected to illustrate how the behaviors of the radical pair [Fe^n-1-OH ·R] determine the eventual reaction outcome. Finally, we discuss the powerful potential of "radical rebound" processes as a general paradigm for developing novel C-H functionalization reactions with synthetic, biomimetic catalysts. We envision that new chemistry will continue to arise by bridging enzymatic "radical rebound" with synthetic organic chemistry.

Iron(II)-Catalyzed Intermolecular Aminofluorination of Unfunctionalized Olefins Using Fluoride Ion

We herein report a new catalytic method for intermolecular olefin aminofluorination using earth-abundant iron catalysts and nucleophilic fluoride ion. This method tolerates a broad range of unfunctionalized olefins, especially nonstyrenyl olefins that are incompatible with existing olefin aminofluorination methods. This new iron-catalyzed process directly converts readily available olefins to internal vicinal fluoro carbamates with high regioselectivity (N vs F), many of which are difficult to prepare using known methods. Preliminary mechanistic studies demonstrate that it is possible to exert asymmetric induction using chiral iron catalysts and that both an iron-nitrenoid and carbocation species may be reactive intermediates.

Copper-Catalyzed Intramolecular Oxidative Amination of Unactivated Internal Alkenes

A copper-catalyzed oxidative amination of unactivated internal alkenes has been developed. The Wacker-type oxidative alkene amination reaction is traditionally catalyzed by a palladium through a mechanism involving aminopalladation and β-hydride elimination. Replacing the precious and scarce palladium with a cheap and abundant copper for this transformation has been challenging because of the difficulty associated with the aminocupration of internal alkenes. The combination of a simple copper salt, without additional ligand, as the catalyst and Dess-Martin periodinane as the oxidant, promotes efficiently the oxidative amination of allylic carbamates and ureas bearing di- and trisubstituted alkenes leading to oxazolidinones and imidazolidinones. Preliminary mechanistic studies suggested a hybrid radical-organometallic mechanism involving an amidyl radical cyclization to form the key C-N bond.

Iron-Catalyzed Direct Diazidation for a Broad Range of Olefins

Reported herein is a new iron-catalyzed diastereoselective olefin diazidation reaction which occurs at room temperature (1-5 mol% of catalysts and d.r. values of up to >20:1). This method tolerates a broad range of both unfunctionalized and highly functionalized olefins, including those that are incompatible with existing methods. It also provides a convenient approach to vicinal primary diamines as well as other synthetically valuable nitrogen-containing building blocks which are difficult to obtain with alternative methods. Preliminary mechanistic studies suggest that the reaction may proceed through a new mechanistic pathway in which both Lewis acid activation and iron-enabled redox-catalysis are crucial for selective azido-group transfer.

Iron(iii) chloride hexahydrate-promoted selective hydroxylation and chlorination of benzyl ketone derivatives for the construction of hetero-quaternary scaffolds

A tunable α-hydroxylation/α-chlorination of benzylketone derivatives for the construction of hetero-quaternary units has been developed by iron(iii) chloride hexahydrate-mediated selective transformations.

Iron(II)-catalyzed asymmetric intramolecular olefin aminochlorination using chloride ion

An iron-catalyzed enantioselective and diastereoselective intramolecular olefin aminochlorination reaction is reported (ee up to 92%, dr up to 15 : 1). In this reaction, a functionalized hydroxylamine and chloride ion are utilized as nitrogen and chlorine sources, respectively. This new method tolerates a range of synthetically valuable internal olefins that are all incompatible with existing asymmetric olefin aminochlorination methods.

A Simple and Efficient Two-Step Synthesis of 1,2,3-Triiodoarenes via Consecutive C–H Iodination/ipso-Iododecarboxylation Strategy: A Potential Application towards ortho-Diiodoarenes by Regioselective Metal–Iodine Exchange Reaction

A general, robust, and efficient method for the conversion of benzoic acids to 1,2,3-triiodoarenes and 1,2,3-trihaloarenes via a two-step synthesis is reported. Commercially available benzoic acids were used that can allow the reactions to be performed on multi-gram scales with good-to-excellent yields. This report discloses a practical method for the synthesis of 1,2,3-triiodoarenes and 1,2,3-trihaloarenes that is general in scope, scalable, and easy to workup and purify. A potential application of the target compounds as precursors for novel regioselective metal–iodine exchange reaction of 1,2,3-triiodoarenes was also demonstrated. It provided ortho-diiodoaryl derivatives in a high regioselective fashion that are useful intermediates in synthesis and indeed are hard to synthesize by any other means.

Iron(II)-catalyzed intermolecular amino-oxygenation of olefins through the N-O bond cleavage of functionalized hydroxylamines

An iron-catalyzed diastereoselective intermolecular olefin amino-oxygenation reaction is reported, which proceeds via an iron-nitrenoid generated by the N-O bond cleavage of a functionalized hydroxylamine. In this reaction, a bench-stable hydroxylamine derivative is used as the amination reagent and oxidant. This method tolerates a range of synthetically valuable substrates that have been all incompatible with existing amino-oxygenation methods. It can also provide amino alcohol derivatives with regio- and stereochemical arrays complementary to known amino-oxygenation methods.