Synthesis of aromatic amides from lignin and its derivatives

Benzamides constitute an important class of bulk and fine chemicals as well as essential parts of many life science molecules. Currently, all these compounds are majorly produced from petrochemical-based feedstocks. Notably the selective aerobic oxidative conversion of lignin and lignin-derived compounds to primary, secondary, and tertiary amides and phenols offers the potential for a more sustainable synthesis of valuable building blocks for fine chemicals, monomers for polymers, biologically active molecules, and diverse consumer products. Here we present the concept of "lignin to amides" which is demonstrated by a one-pot, multi-step oxidation process utilizing molecular oxygen and a 3d-metal catalyst with highly dispersed and stable cobalt species (Co-SACs) supported on nitrogen-doped carbon in water as solvent. Moreover, our cobalt-based methodology allows for the cost-efficient transformation of a lignin and its variety of derivates simply using O2 and organic amines. Mechanistic investigations and control experiments suggest that the process involves an initial dehydrogenation of Cα-OH, cleavage of the Cβ-O as well as C(O)-C bond and condensation of the resulting carboxylic acids with amines. Spectroscopic studies indicate that the formation of superoxide species (O2●-) and specific Co-nitrogen sites anchored on mesoporous carbon sheets are key for the success of this transformation.

Difluorocarbene-Enabled Dehydration of Primary Amides To Access Nitriles

A cost-effective and environmentally friendly method for the direct conversion of primary amides to nitriles was developed using commercially available non-toxic ethyl bromodifluoroacetate as a difluorocarbene precursor under metal-free and ligand-free conditions. The reaction features high yields and tolerates various sensitive moieties, including alkyl, alkenyl, ether, sulfone, sulfoxide, heteroaryl, chloro, bromo, iodo, hydroxyl, nitro, and cyano groups, and late-stage modification of complex molecules is also feasible. Moreover, the present method is effective on large scales, showing potential for industrial application.

Enantioselective Reduction of 1-Naphthamides by Electrochemical Reduction and Catalytic Asymmetric Hydrogenation in Tandem

Chiral 1-tetrahydronaphthamides are the core structures of many bioactive molecules, yet their efficient asymmetric synthesis from a simple feedstock remains a challenge. Herein, we present a one-pot synthesis strategy that combines electrochemical reduction and ruthenium-catalyzed asymmetric hydrogenation to achieve the enantioselective reduction of 1-naphthalenamides to chiral 1-tetrahydronaphthamides. The protocol provides a practical platform for selectively constructing high-value chiral tetrahydronaphthenes from readily available naphthalene feedstock, thereby expanding the scope of asymmetric hydrogenation. The synthetic utility of this protocol is further demonstrated through the synthesis of bioactive molecules.

Transition Metal-Catalyzed Nitrogen Atom Insertion into Carbocycles

ConspectusN-Heterocycles are essential in pharmaceutical engineering, materials science, and synthetic chemistry. Recently, skeletal editing, which involves making specific point changes to the core of a molecule through single-atom insertion, deletion, or transmutation, has gained attention for its potential to modify complex substrates. In this context, the insertion of nitrogen atoms into carbocycles to form N-heterocycles has emerged as a significant research focus in modern synthetic chemistry owing to its novel synthetic logic. This distinctive retrosynthetic approach enables late-stage modification of molecular skeletons and provides a different pathway for synthesizing multiply substituted N-heterocycles. Nevertheless, nitrogen atom insertion into carbocycles has proven challenging because of the inherent inertness of carbon-based skeletons and difficulty in cleaving C-C bonds. Therefore, selective insertion of nitrogen atoms for skeletal editing remains a challenging and growing field in synthetic chemistry. This Account primarily highlights the contributions of our laboratory to this active field and acknowledges the key contributions from other researchers. It is organized into two sections based on the type of the carbocycle. The first section explores the insertion of nitrogen atoms into cycloalkenes. Recent Co-catalyzed oxidative azidation strategies have enabled nitrogen atom insertion into cyclobutenes, cyclopentenes, and cyclohexenes, facilitating the synthesis of polysubstituted pyridines, which has been conventionally challenging through pyridine cross-coupling. The subsequent section highlights our discovery in the realm of nitrogen atom insertion into arenes. The site-selective skeletal editing of stable arenes is challenging in synthetic chemistry. We developed a method for the intramolecular insertion of nitrogen atoms into the benzene rings of 2-amino biaryls by suppressing the competing C-H insertion process by using a paddlewheel dirhodium catalyst. In addition, to address the challenging site-selective issues in nitrogen atom insertion, we employed arenols as substrates, which could act as selective controlling elements in site-selective skeletal editing. We reported a Cu-catalyzed nitrogen atom insertion into arenols, which proceeds through a dearomative azidation/aryl migration process, enabling the site-selective incorporation of nitrogen atoms into arenes. Inspired by this result, we recently extended the reaction model by using a Fe-catalyst to facilitate the ring contraction of the nitrogen-inserted product, achieving the carbon-to-nitrogen transmutation of arenols. Various complex polyaromatic arenols could effectively undergo the desired atom's transmutation, presenting considerable potential for various applications in materials chemistry. In this Account, we present an overview of our achievements in nitrogen atom insertion reactions, with a focus on the reaction scopes, mechanistic features, and synthetic applications. We anticipate that this Account will provide valuable insights and propel the development of innovative methodologies in both skeletal editing and N-heterocycle synthesis.

Molecular Ring Remodeling through C-C Bond Cleavage

ConspectusStable and inert C-C bonds form the fundamental framework of organic compounds. Consequently, direct transformations involving C-C bond cleavage present an innovative approach for the rapid modification and remodeling of molecular skeletons. In recent years, the concept of molecular skeletal editing has garnered widespread attention and has been significantly developed, providing new opportunities for the late-stage modification of bioactive molecules, the high-value transformation of bulk chemicals, and a revolution in the traditional fragment coupling strategies of chemical synthesis. Notable advancements in this field have focused on C-C bond cleavage and the remodeling of cyclic molecules, including ring expansion, ring contraction, and ring-opening reactions, thereby enriching the synthetic toolbox available to chemists. However, selective C-C bond transformation remains a formidable challenge, especially in the remodeling of complex molecules, due to the high bond dissociation energy and the difficulty in achieving precise selectivity control. Over the past few years, our group has made efforts to address these challenges. We have demonstrated the potential of cyclic molecule remodeling reactions as an efficient strategy for the synthesis and modification of complex molecules.Herein, we present two major thematic advancements achieved by our group, utilizing cascade activation and entropy-driven reconstruction strategies for molecular ring remodeling via C-C bond cleavage. These strategies are characterized by mild conditions, the accessibility of catalysts and reagents, and exceptional functional group compatibility, thereby emerging as novel approaches for molecular ring remodeling through atom-incorporation reactions mainly on nitrogenation, oxygenation, and halogenation to synthesize pharmaceuticals, natural products, and material molecules. (1) Ring expansion reactions: We developed novel reactions that enable the insertion of C-, N-, and O-containing units into molecular rings. These methodologies offer practical and efficient routes for synthesizing amides, amines, lactones, and nitrogen-containing heterocycles. (2) Ring-opening reactions: C-C bond cleavage in ring-opening reactions enables the efficient construction of distally difunctionalized molecular frameworks. By utilizing a transition metal catalysis and radical-mediated process, we have successfully achieved the cleavage of both C-C single bonds and C═C double bonds within molecular rings. Furthermore, we have tackled the highly challenging arene ring-opening (ARO) reaction, enabling the construction of stereoselective conjugated systems through the unsaturation liberation of aromatic systems. Mechanistic studies and DFT calculations have provided critical insights into these processes. We have also identified key intermediates involved in C-C bond cleavage, including benzyl azide, O-acetyl hydroxylamine, β-azido peroxyl radical, copper bisnitrene, and 2-nitrene indazole. These findings have deepened our understanding of the mechanisms and the entropy-driven reconstruction strategy, which has further promoted the discovery of related C-C bond transformations of acyclic substrates.

Solvent-controlled silver catalyzed radical transformation of α-imino-oxy acids with cyclic aldimines

A silver-catalyzed cross coupling of cyclic aldimines and α-imino-oxy acids has been developed. The solvent-dependent reaction could selectively deliver either cyclic imine moiety retained nitriles or ring-opened oxonitriles in moderate yields. The mechanistic studies show that the reaction undergoes a radical pathway.

Rapid Synthesis of Primary Amides Using Ammonia Borane

We report the rapid synthesis of primary amides by directly using commercially available ammonia borane (NH3·BH3), sodium hexamethyldisilazide (NaHMDS), and esters. The success of this protocol relies on NH3·BH3 as the nitrogen source being considerably more convenient and NaHMDS being an excellent proton abstractor but not participating in the nucleophilic addition reaction. The reaction had a wide substrate scope containing bioactive molecules, and most of the substrates were efficiently amidated over 90% yields.

Catalytic Aerobic Carbooximation of Alkenes Using Secondary Nitroalkanes as Both α-Nitro Alkyl Radical and Nitrogen Monoxide Sources

Aerobic nitro-nitrite isomerization of secondary nitroalkanes is postulated to proceed via the intermediacy of the α-nitro alkyl radical, where the corresponding Nef-type products, ketones, and nitrogen monoxide can be obtained as byproducts. To explore the catalytic aerobic carbooximation of alkenes using secondary nitroalkanes, phase-transfer catalysis of KSeCN and TBAI has been developed. The current aerobic carbooximation of alkenes utilizes nitroalkanes as both radical and nitrogen monoxide sources in water without external oxidants and prefunctionalized nitroalkanes.

Cu-Catalyzed Electrochemical Activation of Nitromethane to Access Aldoxime-Substituted Nitrile Oxide for Huisgen Reaction

Here, we report an electrochemical approach to generate an aldoxime-substituted nitrile oxide via the activation of nitromethane. The Cu-catalyzed Huisgen reaction of this 1,3-dipole with alkynes enables successful preparation of 48 new isoxazole aldoximes, which are typically challenging to synthesize by other methods, in 52 to 97% yields with excellent regioselectivity and chemoselectivity in a single step. Moreover, 20 3,3'-bisisoxazoles are prepared from the isoxazole aldoxime products in good yields via a two-step sequence.

Electrophilic Intermediates in the Nef and Meyer Reactions: A Computational Study

The generation, interconversion, and reactivity of electrophilic species generated upon activation of nitroalkanes with protic acids (the Nef and Meyer reactions) were investigated by quantum-chemical calculations. N,N-Bis(hydroxy)iminium (R2C═N+(OH)2) and N-oxoiminium (R2C═N+═O) cations were shown to be produced independently from aci-nitroalkanes, while N-hydroxynitrilium cations (RC≡N+-OH) were formed via nearly barrierless C-H bond cleavage in N-oxoiminium cations. The N-oxoiminium and N-hydroxynitrilium cations whose formation is favored under highly acidic anhydrous conditions are strong electrophiles capable of reacting even with nonactivated arenes under ambient conditions. The N-oxoiminium cations R2C═N+═O are highly unusual ambident species containing three contiguous electrophilic centers (C, N, and O atoms). Nucleophilic addition at the oxygen atom is less preferred than the C- and N-attack yet possible in an intramolecular variant. These computational results shed light on some key aspects of the mechanisms of the Nef and Meyer reactions and predict the possibility of numerous interrupted versions of these reactions.

Anilines Formation via Molybdenum-Catalyzed Intermolecular Reaction of Ynones with Allylic Amines

The multi-substituted anilines are widely found in organic synthesis, medicinal chemistry and material science. The quest for robust and efficient methods to construct a diverse array of these compounds using readily accessible starting materials under simple reaction conditions is of utmost importance. Here, we report an unprecedented and efficient approach for the synthesis of 2,4-di and 2,4,6-trisubstituted anilines. With a simple molybdenum(VI) catalyst, a wide range of 2,4-di and 2,4,6-trisubstituted anilines were efficiently prepared in generally good to excellent yields from readily accessible ynones and allylic amines. The synthetic potential of this methodology was further underscored by its applications in several synthetic transformations, gram-scale reactions, and derivatization of bioactive molecules. Preliminary mechanistic studies suggested that this aniline formation might involve a cascade of aza-Michael addition, [1,6]-proton shift, cyclization, dehydration, 6π-electrocyclization, and aromatization. This novel strategy provided a robust, simple, and modular approach for the syntheses of various valuable di- or trisubstituted anilines, some of which were otherwise challenging to access.

HFIP-driven Schmidt-type reaction enables chromone-3-carbonitriles and its applications

Chromone-3-carbonitrile has been extensively studied in a panel of high-value transformations. However, existing protocols for the synthesis of this scaffold are often constrained by the structure of the starting materials and harsh conditions. To address these issues, we present a novel strategy that HFIP (hexafluoroisopropanol)-driven strategy, enables chromone-3-carbonitriles synthesis without undesirable side reactions. This protocol features readily available feedstocks, mild conditions, catalytic amount of acid and good to excellent yields. The utility of this chemistry is further demonstrated by amenable modifications of chromone-pyrimidines and imidazoles. Moreover, the analogous transformation of aldehydes is successfully constructed to achieve useful compounds such as 2-hydroxybenzonitriles, heterocyclic nitriles, and α, β-unsaturated nitriles. The HFIP-driven strategy offers an interesting access to different types of nitriles in a sustainably manner.

Selective Upcycling of Polyolefins into High-Value Nitrogenated Chemicals

The selective upcycling of polyolefins to create products of increased value has emerged as an innovative approach to carbon resource stewardship, drawing significant scientific and industrial interest. Although recent advancements in recycling technology have facilitated the direct conversion of polyolefins to hydrocarbons or oxygenated compounds, the synthesis of nitrogenated compounds from such waste polyolefins has not yet been disclosed. Herein, we demonstrate a novel approach for the upcycling of waste polyolefins by efficiently transforming a range of postconsumer plastic products into nitriles and amides. This process leverages the catalytic properties of manganese dioxide in combination with an inexpensive nitrogen source, urea, to make it both practical and economically viable. Our approach not only opens new avenues for the creation of nitrogenated chemicals from polyolefin waste but also underscores the critical importance of recycling and valorizing carbon resources originally derived from fossil fuels. This study provides a new upcycling strategy for the sustainable conversion of waste polyolefins.

Generation of New Synthons for Synthesis Through Activation of Nitromethane

Nitromethane is used as a common solvent, stabilizer, and fuel additive. Nitromethane has also been used as a sustainable building block and convenient reagent in chemical synthesis. In this Minireview, we summarize the recent advances in activation of nitromethane, using nitromethane as the source of cyano group, nitrogen, methylamine, formyl group, C1, nitroso, and oxime.

Palladium-Catalyzed Synthesis of β-Alkynyl Ketones via Selective 1,3-Alkynyl Migration of α,α-Disubstituted Allylic Alcohols

Herein, a palladium-catalyzed 1,3-alkynyl migration of allylic alcohol for the synthesis of β-alkynyl ketone was described. This intramolecular rearrangement reaction demonstrated an enhanced reactivity compared to the traditional intermolecular alkynylation by circumventing the dimerization of alkynes, exhibiting a specific selectivity toward β-alkynyl elimination. Moreover, this reaction featured wide substrate scope, good functional group tolerance, and 100% atom economy.

Visible light-driven molecular oxygen activation for oxidative amidation of alcohols using lead-free metal halide perovskite

Herein, we report the modulation of the band structures of halide perovskite Cs2CuBr4 by tuning the synthesis methods. The photocatalyst PC-1, synthesized by the hot injection method, has a more negative conduction band minima (CBM) than the photocatalyst PC-2, synthesized at room temperature. As a result, PC-1 can activate molecular O2 more efficiently to initiate the radical-mediated dehydrogenation of alcohols. The more positive valence band maxima (VBM) of PC-1 also facilitates amine oxidation to the corresponding radical. Further, improved charge separation and transport and a decrement in the photogenerated charge carrier recombination have been detected for PC-1 to enhance photocatalytic activity. PC-1 showed improved yields for a series of structurally diverse amides (highest yield = 98%) by oxidative amidation of alcohols under visible light irradiation.

Selective nitrogen insertion into aryl alkanes

Molecular structure-editing through nitrogen insertion offers more efficient and ingenious pathways for the synthesis of nitrogen-containing compounds, which could benefit the development of synthetic chemistry, pharmaceutical research, and materials science. Substituted amines, especially nitrogen-containing alkyl heterocyclic compounds, are widely found in nature products and drugs. Generally, accessing these compounds requires multiple steps, which could result in low efficiency. In this work, a molecular editing strategy is used to realize the synthesis of nitrogen-containing compounds using aryl alkanes as starting materials. Using derivatives of O-tosylhydroxylamine as the nitrogen source, this method enables precise nitrogen insertion into the Csp2-Csp3 bond of aryl alkanes. Notably, further synthetic applications demonstrate that this method could be used to prepare bioactive molecules with good efficiency and modify the molecular skeleton of drugs. Furthermore, a plausible reaction mechanism involving the transformation of carbocation and imine intermediates has been proposed based on the results of control experiments.

Carbene-Assisted Arene Ring-Opening

Despite the significant achievements in dearomatization and C-H functionalization of arenes, the arene ring-opening remains a largely unmet challenge and is underdeveloped due to the high bond dissociation energy and strong resonance stabilization energy inherent in aromatic compounds. Herein, we demonstrate a novel carbene assisted strategy for arene ring-opening. The understanding of the mechanism by our DFT calculations will stimulate wide application of bulk arene chemicals for the synthesis of value-added polyconjugated chain molecules. Various aryl azide derivatives now can be directly converted into valuable polyconjugated enynes, avoiding traditional synthesis including multistep unsaturated precursors, poor selectivity control, and subsequent transition-metal catalyzed cross-coupling reactions. The simple conditions required were demonstrated in the late-stage modification of complex molecules and fused ring compounds. This chemistry expands the horizons of carbene chemistry and provides a novel pathway for arene ring-opening.

Cobalt-Catalyzed Acceptorless Dehydrogenation of Primary Amines to Nitriles

The direct double dehydrogenation from primary amines to nitriles without an oxidant or hydrogen acceptor is both intriguing and challenging. In this paper, we describe a non-noble metal catalyst capable of realizing such a transformation with high efficiency. A cobalt-centered N,N-bidentate complex was designed and employed as a metal-ligand cooperative dehydrogenation catalyst. Detailed kinetic studies, control experiments, and DFT calculations revealed the crucial hydride transfer, proton transfer, and hydrogen evolution processes. Finally, a tandem outer-sphere/inner-sphere mechanism was proposed for the dehydrogenation of amines to nitriles through an imine intermediate.

Catalytic 1,1-diazidation of alkenes

Compared to well-developed catalytic 1,2-diazidation of alkenes to produce vicinal diazides, the corresponding catalytic 1,1-diazidation of alkenes to yield geminal diazides has not been realized. Here we report an efficient approach for catalytic 1,1-diazidation of alkenes by redox-active selenium catalysis. Under mild conditions, electron-rich aryl alkenes with Z or E or Z/E mixed configuration can undergo migratory 1,1-diazidation to give a series of functionalized monoalkyl or dialkyl geminal diazides that are difficult to access by other methods. The method is also effective for the construction of polydiazides. The formed diazides are relatively safe by TGA-DSC analysis and impact sensitivity tests, and can be easily converted into various valuable molecules. In addition, interesting reactivity that geminal diazides give valuable molecules via the geminal diazidomethyl moiety as a formal leaving group in the presence of Lewis acid is disclosed. Mechanistic studies revealed that a selenenylation-deselenenylation followed by 1,2-aryl migration process is involved in the reactions, which provides a basis for the design of new reactions.

Exploring Chemical Reaction Space with Machine Learning Models: Representation and Feature Perspective

Chemical reactions serve as foundational building blocks for organic chemistry and drug design. In the era of large AI models, data-driven approaches have emerged to innovate the design of novel reactions, optimize existing ones for higher yields, and discover new pathways for synthesizing chemical structures comprehensively. To effectively address these challenges with machine learning models, it is imperative to derive robust and informative representations or engage in feature engineering using extensive data sets of reactions. This work aims to provide a comprehensive review of established reaction featurization approaches, offering insights into the selection of representations and the design of features for a wide array of tasks. The advantages and limitations of employing SMILES, molecular fingerprints, molecular graphs, and physics-based properties are meticulously elaborated. Solutions to bridge the gap between different representations will also be critically evaluated. Additionally, we introduce a new frontier in chemical reaction pretraining, holding promise as an innovative yet unexplored avenue.

Asymmetric Tandem Michael Addition/Interrupted Nef Reactions of Nitromethane with Oxindole-Derived Alkenes: Enantioselective Synthesis of Spiro-polycyclic Oxindoles

Chiral spiro-polycyclic oxindoles are valuable heterocyclic ring systems that are widely distributed in natural alkaloids and biologically active compounds. Herein, we reported an asymmetric tandem Michael addition/interrupted Nef reaction of nitromethane with oxindole-derived alkenes catalyzed by a chiral 2-aminobenzimidazole bifunctional organocatalyst. A series of novel enantiomerically enriched spiro-polycyclic oxindole derivatives bearing an oxime group were synthesized in moderate to excellent isolated yields (up to 99%) with an excellent level of enantioselectivities (up to 99% ee). Furthermore, the antiproliferation activity of the resulting oxindoles derivatives were evaluated, and compound 2d demonstrated promising anticancer properties against HCT116 (IC50 = 14.08 μM) and HT29 (IC50 = 15.46 μM) cell lines.

Late-stage modification of bioactive compounds: Improving druggability through efficient molecular editing

Synthetic chemistry plays an indispensable role in drug discovery, contributing to hit compounds identification, lead compounds optimization, candidate drugs preparation, and so on. As Nobel Prize laureate James Black emphasized, "the most fruitful basis for the discovery of a new drug is to start with an old drug"1. Late-stage modification or functionalization of drugs, natural products and bioactive compounds have garnered significant interest due to its ability to introduce diverse elements into bioactive compounds promptly. Such modifications alter the chemical space and physiochemical properties of these compounds, ultimately influencing their potency and druggability. To enrich a toolbox of chemical modification methods for drug discovery, this review focuses on the incorporation of halogen, oxygen, and nitrogen-the ubiquitous elements in pharmacophore components of the marketed drugs-through late-stage modification in recent two decades, and discusses the state and challenges faced in these fields. We also emphasize that increasing cooperation between chemists and pharmacists may be conducive to the rapid discovery of new activities of the functionalized molecules. Ultimately, we hope this review would serve as a valuable resource, facilitating the application of late-stage modification in the construction of novel molecules and inspiring innovative concepts for designing and building new drugs.

A Catalytic Method to Activate Nitromethane by the Cooperation of Homo- and Heterogeneous Catalysis

The achievement of directly activating and utilizing bulk small molecules has remained a longstanding objective in the field of chemical synthesis. The present work reports a catalytic activation method for bulk chemical nitromethane (MeNO2 ). This method combines homogeneous Lewis acid with recyclable heterogeneous Brønsted acid catalysis, featuring practicality, sustainability, and low cost, thus solving the inherent drawbacks of previous Nef processes where stoichiometric reductants or activators were required. By combining the advantages of both homo- and heterogeneous catalysts, this chemistry may not only offer new opportunities for the further development of MeNO2 as a nitrogen source for organic synthesis, but also promote the catalysis design in synthetic chemistry.

Tf2O-Mediated Tandem Reaction of Enaminones for the Synthesis of Functionalized Conjugated-Enals/β-Naphthalaldehydes

A highly efficient and regioselective method for constructing functionalized conjugated enals via the Tf2O-mediated tandem reaction of enaminones with thiophenols has been described. Chain products with excellent stereoselectivity could be obtained through substrate regulation. Additionally, a feasible method for synthesizing β-naphthalaldehydes through PhSO2Na/DABCO promoting hydrogen atom transfer process has also been reported here. Mechanism studies have shown that 2-formyl vinyl triflate 8 and sulfonylated enal 9 were the key intermediates in this process.

Carbon-Carbon Bond Cleavage for Late-Stage Functionalization

Late-stage functionalization (LSF) introduces functional group or structural modification at the final stage of the synthesis of natural products, drugs, and complex compounds. It is anticipated that late-stage functionalization would improve drug discovery's effectiveness and efficiency and hasten the creation of various chemical libraries. Consequently, late-stage functionalization of natural products is a productive technique to produce natural product derivatives, which significantly impacts chemical biology and drug development. Carbon-carbon bonds make up the fundamental framework of organic molecules. Compared with the carbon-carbon bond construction, the carbon-carbon bond activation can directly enable molecular editing (deletion, insertion, or modification of atoms or groups of atoms) and provide a more efficient and accurate synthetic strategy. However, the efficient and selective activation of unstrained carbon-carbon bonds is still one of the most challenging projects in organic synthesis. This review encompasses the strategies employed in recent years for carbon-carbon bond cleavage by explicitly focusing on their applicability in late-stage functionalization. This review expands the current discourse on carbon-carbon bond cleavage in late-stage functionalization reactions by providing a comprehensive overview of the selective cleavage of various types of carbon-carbon bonds. This includes C-C(sp), C-C(sp2), and C-C(sp3) single bonds; carbon-carbon double bonds; and carbon-carbon triple bonds, with a focus on catalysis by transition metals or organocatalysts. Additionally, specific topics, such as ring-opening processes involving carbon-carbon bond cleavage in three-, four-, five-, and six-membered rings, are discussed, and exemplar applications of these techniques are showcased in the context of complex bioactive molecules or drug discovery. This review aims to shed light on recent advancements in the field and propose potential avenues for future research in the realm of late-stage carbon-carbon bond functionalization.

Metal Free Dötz-Type Aminobenzannulation Reaction via 1,1-Dipoles Cross-Coupling

Aryl amines are of constant interest in organic synthesis owing to their ubiquity in natural products, pharmaceuticals, and organic materials. However, C-H amination or pre-functionalization frequently results in uncontrollable site selectivity, over activation and the generation of inseparable mixtures of regio-isomers. Here we present a novel metal free Dötz-type aminobenzannulation reaction that circumvents the selectivity issues inherent in aromatic chemistry, as well as the use of stoichiometric unstable organolithium reagents and toxic chromium complexes. The concept of utilizing readily available isocyanides and Morita-Baylis-Hillman (MBH) carbonates to achieve 1,1-dipoles cross-coupling to construct ketenimine is the key to success, which has been experimentally and computationally verified. The tandem 6π-electrocyclization/aromatization process offers a versatile method for synthesizing functionalized anilines, fused aryl amines and fused heteroaryl amines.

Aminodealkenylation: Ozonolysis and copper catalysis convert C(sp3)-C(sp2) bonds to C(sp3)-N bonds

Great efforts have been directed toward alkene π bond amination. In contrast, analogous functionalization of the adjacent C(sp3)-C(sp2) σ bonds is much rarer. Here we report how ozonolysis and copper catalysis under mild reaction conditions enable alkene C(sp3)-C(sp2) σ bond-rupturing cross-coupling reactions for the construction of new C(sp3)-N bonds. We have used this unconventional transformation for late-stage modification of hormones, pharmaceutical reagents, peptides, and nucleosides. Furthermore, we have coupled abundantly available terpenes and terpenoids with nitrogen nucleophiles to access artificial terpenoid alkaloids and complex chiral amines. In addition, we applied a commodity chemical, α-methylstyrene, as a methylation reagent to prepare methylated nucleosides directly from canonical nucleosides in one synthetic step. Our mechanistic investigation implicates an unusual copper ion pair cooperative process.

FeCl3-catalyzed oxidative amidation of benzylic C-H bonds enabled by a photogenerated chlorine-radical

Herein, we report the development of iron-catalyzed benzylic C-H oxidative amidation reactions via photoinduced ligand-to-metal charge transfer (LMCT). These reactions exhibit a broad substrate scope (60 examples) and offer operationally simple, scalable procedures for accessing valuable products from methylarenes in a single step. Mechanistic studies and control experiments confirm the participation of a photogenerated chlorine radical in facilitating the hydrogen atom transfer (HAT) from the benzylic C-H bond to initiate the reaction.

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.

Condition-Controlled O-Acylation and N-O Bond Reduction of Hydroximic Acids with Thioacetic Acid

Condition-dependent transformations between hydroximic acids and thioacetic acid were achieved. Using NH₄HCO₃ in the ethanol solvent, efficient N-O bond cleavage of hydroxamic acids occurred to afford primary amides with high functional group compatibility. The reaction was switched to O-acylation when NEt₃ and H₂O were used as the base and solvent, respectively. These facile transformations could be scaled up to the gram level smoothly. Preliminary mechanistic studies suggested that the N-O bond cleavage involves a cascade process of acylation/reduction.

Engineered aldoxime dehydratase to enable the chemoenzymatic conversion of benzyl amines to aromatic nitriles

A chemoenzymatic strategy has been implemented to synthesize nitriles from benzyl amines under mild conditions. Aldoxime dehydratase (Oxd) plays a decisive role to convert aldoximes into corresponding nitriles. However, natural Oxds commonly exhibit extremely low catalytic capacity toward benzaldehyde oximes. Here, we engineered the OxdF1 from Pseudomonas putida F1 to enhance its catalytic efficiency toward benzaldehyde oximes by a semi-rational design strategy. The protein structure-based CAVER analysis indicates that M29, A147, F306, and L318 are located adjacent to the substrate tunnel entrance of OxdF1, which were responsible for the transportation of substrate into the active site. After two rounds of mutagenesis, the maximum activities of the mutants L318F and L318F/F306Y were 2.6 and 2.8 U/mg respectively, which were significantly higher than the wild OxdF1 of 0.7 U/mg. Meanwhile, the lipase type B from Candida antarctica was functionally expressed in Escherichia coli cells to selectively oxidize benzyl amines to aldoximes using urea-hydrogen peroxide adduct (UHP) as an oxidant in ethyl acetate. To merge the oxidation and dehydration reactions, a reductive extraction solution was added to remove the residue UHP, which is critical to eliminate its inhibition on the Oxd activity. Consequently, nine benzyl amines were efficiently converted into corresponding nitriles by the chemoenzymatic sequence.

Recent Applications of Trifluoromethanesulfonic Anhydride in Organic Synthesis

Trifluoromethanesulfonic anhydride has been widely used in synthetic organic chemistry, not only for the conversion of various oxygen-containing compounds to the triflates, but also for the electrophilic activation and further conversion of amides, sulfoxides, and phosphorus oxides. In recent years, the utilization of Tf₂ O as an activator for nitrogen-containing heterocycles, nitriles and nitro groups has become a promising tool for the development of new valuable methods with considerable success. In addition, Tf₂ O has been used as an efficient radical trifluoromethylation and trifluoromethylthiolation reagent due to the contained SO₂ CF₃ fragment, and significant progress has been made in this area. This review summarizes the recent progress in the applications of Tf₂ O in the above two aspects, and aims to illustrate the role and potential application of this reagent in organic synthesis.

Microtubules as a potential platform for energy transfer in biological systems: a target for implementing individualized, dynamic variability patterns to improve organ function

Variability characterizes the complexity of biological systems and is essential for their function. Microtubules (MTs) play a role in structural integrity, cell motility, material transport, and force generation during mitosis, and dynamic instability exemplifies the variability in the proper function of MTs. MTs are a platform for energy transfer in cells. The dynamic instability of MTs manifests itself by the coexistence of growth and shortening, or polymerization and depolymerization. It results from a balance between attractive and repulsive forces between tubulin dimers. The paper reviews the current data on MTs and their potential roles as energy-transfer cellular structures and presents how variability can improve the function of biological systems in an individualized manner. The paper presents the option for targeting MTs to trigger dynamic improvement in cell plasticity, regulate energy transfer, and possibly control quantum effects in biological systems. The described system quantifies MT-dependent variability patterns combined with additional personalized signatures to improve organ function in a subject-tailored manner. The platform can regulate the use of MT-targeting drugs to improve the response to chronic therapies. Ongoing trials test the effects of this platform on various disorders.

Catalytic Aerobic N-Nitrosation by Secondary Nitroalkanes in Water: A Tandem Diazotization of Aryl Amines and Azo Coupling

Secondary nitroalkanes underwent oxygen-mediated nitro-nitrite isomerization, serving as versatile N-nitrosating agents under aerobic conditions. To capitalize on the newly discovered aerobic nitro-nitrite isomerization phenomenon, a phase-transfer catalysis system employing KSeCN and TBAI was developed, in which the tandem diazotization and azo coupling with nitroalkanes as well as N-nitrosation of amines were accomplished. The current tandem diazotization and azo coupling strategy provides a facile synthesis of areneazo-2-(2-nitro)propane derivatives, a safe synthetic alternative to aryl diazonium salts.

High Nitrile Yields of Aerobic Ammoxidation of Alcohols Achieved by Generating •O2- and Br• Radicals over Iron-Modified TiO2 Photocatalysts

Catalytic ammoxidation of alcohols into nitriles is an essential reaction in organic synthesis. While highly desirable, conducting the synthesis at room temperature is challenging, using NH₃ as the nitrogen source, O₂ as the oxidant, and a catalyst without noble metals. Herein, we report robust photocatalysts consisting of Fe(III)-modified titanium dioxide (Fe/TiO₂) for ammoxidation reactions at room temperature utilizing oxygen at atmospheric pressure, NH₃ as the nitrogen source, and NH₄Br as an additive. To the best of our knowledge, this is the first example of catalytic ammoxidation of alcohols over a photocatalyst using such cheap and benign materials. Various (hetero) aromatic nitriles were synthesized at high yields, and aliphatic alcohols could also be transformed into corresponding nitriles at considerable yields. The modification of TiO₂ with Fe(III) facilitates the formation of active ^•O₂^- radicals and increases the adsorption of NH₃ and amino intermediates on the catalyst, accelerating the ammoxidation to yield nitriles. The additive NH₄Br impressively improves the catalytic efficiency via the formation of bromine radicals (Br^•) from Br^-, which works synergistically with ^•O₂^- to capture H^• from C_α-H, which is present in benzyl alcohol and the intermediate aldimine (RCH═NH), to generate the active carbon-centered radicals. Further, the generation of Br^• from the Br^- additive consumes the photogenerated holes and OH^• radicals to prevent over-oxidation, significantly improving the selectivity toward nitriles. This amalgamation of function and synergy of the Fe(III)-doped TiO₂ and NH₄Br reveals new opportunities for developing semiconductor-based photocatalytic systems for fine chemical synthesis.

Azoarene activation for Schmidt-type reaction and mechanistic insights

The Schmidt rearrangement, a reaction that enables C-C or C-H σ bond cleavage and nitrogen insertion across an aldehyde or ketone substrate, is one of the most important and widely used synthetic tools for the installation of amides and nitriles. However, such a reaction frequently requires volatile, potentially explosive, and highly toxic azide reagents as the nitrogen donor, thus limiting its application to some extent. Here, we show a Schmidt-type reaction where aryldiazonium salts act as the nitrogen precursor and in-situ-generated cyclopenta-1,4-dien-1-yl acetates serve as pronucleophiles from gold-catalyzed Nazarov cyclization of 1,3-enyne acetates. Noteworthy is that cycloketone-derived 1,3-enyne acetates enabled ring-expansion relay to access a series of 2-pyridone-containing fused heterocycles, in which nonsymmetric cycloketone-derived counterparts demonstrated high regioselectivity. Aside from investigating the scope of this Schmidt-type reaction, mechanistic details of this transformation are provided by performing systematic theoretical calculations.

Electrosynthesis of formamide from methanol and ammonia under ambient conditions

Electrochemical conversion of abundant carbon- and nitrogen-containing small molecules into high-valued organonitrogen compounds is alluring to reducing current dependence on fossil energy. Here we report a single-cell electrochemical oxidation approach to transform methanol and ammonia into formamide under ambient conditions over Pt electrocatalyst that provides 74.26% selectivity from methanol to formamide and a Faradaic efficiency of 40.39% at 100 mA cm-2 current density, gaining an economic advantage over conventional manufacturing based on techno-economic analysis. A 46-h continuous test performed in the flow cell shows no performance decay. The combined results of in situ experiments and theoretical simulations unveil the C-N bond formation mechanism via nucleophilic attack of NH3 on an aldehyde-like intermediate derived from methanol electrooxidation. This work offers a way to synthesize formamide via C-N coupling and can be extended to substantially synthesize other value-added organonitrogen chemicals (e.g., acetamide, propenamide, formyl methylamine).

Electrochemical Oxidative C-C Bond Cleavage of Ketones for C-N Bond Formation: A Route to Amides

Herein, we report an efficient electrochemical activation of the C-C bond of aryl ketones for the preparation of amides under catalyst- and external-oxidant-free conditions using aliphatic amines as the N source. Under environmentally benign electrolysis conditions, a series of amides were synthesized in good yield. Our control experiments revealed that electricity plays an important role in this transformation.

Stereospecific Nitrogen Insertion Using Amino Diphenylphosphinates: An Aza-Baeyer-Villiger Rearrangement

Amino diphenylphosphinates, which are commercially available or easily prepared from hydroxylamine, undergo ring expansion of cyclobutanones toward γ-lactams under mild conditions. A reaction pathway profoundly different from the common Beckmann reaction is achieved through the ambivalent character of the aminating agent. Thus, rearrangement occurs from a Criegee-like intermediate prior to the formation of the oxime species, which is corroborated by mechanistic experiments. Based on this observation, the migrating aptitude of the adjacent groups is analyzed and found to be in line with the parent Baeyer-Villiger reaction rendering a regioselective (up to >99:1 rr), stereospecific (>99% enantiospecificity), and chemoselective (>99%) insertion process possible. The method thus qualifies for late-stage skeletal editing as showcased by the synthesis of Rolipram and its N-alkylated analogs.

Programing a cyanide-free transformation of aldehydes to nitriles and one-pot synthesis of amides through tandem chemo-enzymatic cascades

Nitriles are broadly applied to synthesize pharmaceuticals, agrochemicals, and materials because of their versatile transformation. Although various methods have been developed for introducing a nitrile group into organic molecules, most of them entail the use of highly toxic chemicals, transition metals, or harsh conditions. In this work, we reported a greener chemo-enzymatic cascade to synthesize alky and aryl nitriles from readily accessible aldehydes, that were further transformed into corresponding amides via an artificial enzyme cascade. A biphasic reaction system was designed to bridge chemical synthesis and enzymatic catalysis through simple phase separation. The biphasic system mainly perfectly avoided the inactivation of hydroxylamine on aldoxime dehydratase from Pseudomonas putida (OxdF1) and nitrile hydratase from Aurantimonas manganoxydans ATCC BAA-1229 (NHase1229). For the synthesis of various nitriles, moderate isolation yields of approximately 60% were obtained by the chemo-enzymatic cascade. Interestingly, two seemingly conflicting reactions of dehydration and hydration were sequentially proceeded to synthesize amides by the synergistic catalysis of OxdF1 and NHase1229 in E. coli cells. An isolation yield of approximately 62% was achieved for benzamide at the one-liter scale. In addition, the shuttle transport of substrates and products between two phases is convenient for the product separation and n-hexane recycling. Thus, the chemo-enzymatic cascade shows a potential application in the cyanide-free and large-scale synthesis of nitriles and amides.

A chemo-enzymatic cascade was developed for the cyanide-free synthesis of nitriles from aldehydes and further one-pot transformation into amides.

Chemoselective Primary Amination of Aryl Boronic Acids by PIII/PV═O-Catalysis: Synthetic Capture of the Transient Nef Intermediate HNO

A catalytic approach to intercept the transient HNO for a chemoselective primary amination of arylboronic acids is reported. A phosphetane-based catalyst operating within P^III/P^V═O redox cycling is shown to capture HNO, generated in situ by Nef decomposition of 2-nitropropane, to selectively install the primary amino group at aryl C_sp2 centers. The method furnishes versatile primary arylamines from arylboronic acid substrates with the preservation of otherwise reactive functional groups.

Electrochemical Aerobic Oxidative Cleavage of (sp3)C-C(sp3)/H Bonds in Alkylarenes

An electrochemistry-promoted oxidative cleavage of (sp³)C-C(sp³)/H bonds in alkylarenes was developed. Various aryl alkanes can be smoothly converted into ketones/aldehydes under aerobic conditions using a user-friendly undivided cell setup. The features of air as oxidant, scalability, and mild conditions make them attractive in synthetic organic chemistry.

Copper(II)-β-cyclodextrin immobilized on graphitic carbon nitride nanosheets as a highly effective catalyst for tandem oxidative amidation of benzylic alcohols

In this study, an efficient catalyst based on graphitic carbon nitride nanosheets (CN) and copper(II) supported β-cyclodextrin (β-CD/Cu(II)) was synthesized and used for tandem oxidative amidation of benzylic alcohols. In this regard, CN was functionalized by β-CD/Cu(II) via 1,3-dibromopropane linker (CN-Pr-β-CD/Cu(II)). The prepared catalyst was characterized using FT-IR, XRD, FE-SEM, EDS, TGA, ICP-OES, BET, and TEM analyses. CN-Pr-β-CD/Cu(II) was subsequently applied in a direct oxidative amidation reaction and it was observed that different benzyl alcohols were converted to desire amides with good to excellent efficiency. This reaction was performed in the presence of amine hydrochloride salts, tert-butyl hydroperoxide (TBHP), and Ca2CO3 in acetonitrile (CH3CN) under nitrogen atmosphere. CN-Pr-β-CD/Cu(II) can be recycled and reused five times without significant reduction in reaction efficiency.