Aerobic copper-catalyzed organic reactions

Efficient synthesis of novel phenanthroline-dimedone derivatives using Pd@HQBI-SPION as a versatile palladium-immobilized catalyst

This paper presents the synthesis and application of a novel catalyst for carbon-carbon bond formations, comprising palladium immobilized on 2-(5-hydroxyquinolin-8-yl)-1H-benzo[d]imidazole-5-carboxylic acid modified superparamagnetic iron oxide nanoparticles (Pd@HQBI-SPION). The synthesis involved the attachment of HQBI ligands to SPION using APTES, followed by the immobilization of palladium. Characterization techniques, including FTIR, TEM, and magnetic measurements, confirmed the successful synthesis and structural integrity of Pd@HQBI-SPION. The catalytic activity of Pd@HQBI-SPION was evaluated in various carbon-carbon bond formation reactions, demonstrating high efficiency and reusability. 8 different derivatives bearing several electron withdrawing and electron donating functionalities were used as starting materials and the products were obtained in high isolated yields (75-97%). The catalyst exhibited excellent performance in one-pot synthesis of phenanthroline-dimedone polycyclic derivatives via C-alkylation followed by intramolecular O-alkylation of phenanthroline with dimedone. The products are obtained in high to excellent yields is described. This protocol presents a highly selective synthetic method for the construction of polycyclic aromatic compounds containing nitrogen and oxygen atoms.

Metallaelectro-catalyzed alkyne annulations via C-H activations for sustainable heterocycle syntheses

Alkyne annulation represents a versatile and powerful strategy for the assembly of structurally complex compounds. Recent advances successfully enabled electrocatalytic alkyne annulations, significantly expanding the potential applications of this promising technique towards sustainable synthesis. The metallaelectro-catalyzed C-H activation/annulation stands out as a highly efficient approach that leverages electricity, combining the benefits of electrosynthesis with the power of transition-metal catalyzed C-H activation. Particularly attractive is the pairing of the electro-oxidative C-H activation with the valuable hydrogen evolution reaction (HER), thereby addressing the growing demand for green energy solutions. Herein, we provide an overview of the evolution of electrochemical C-H annulations with alkynes for the construction of heterocycles, with a topical focus on the underlying mechanism manifolds.

Quinoline Synthesis: Nanocatalyzed Green Protocols-An Overview

Heterocyclic compounds are of great interest in our daily lives. They are widely distributed in nature and are synthesized in laboratories. Heterocycles play an important role in the metabolism of all living cells, including vitamins and coenzyme precursors like thiamine and riboflavin. Furthermore, heterocyclic systems are essential building blocks for creating innovative materials with intriguing electrical, mechanical, and biological properties. Also, more than 85% of all biologically active chemical entities comprise a heterocycle. As a result, heterocycle synthesis piqued researchers' curiosity, and in recent decades, chemists have concentrated more on nitrogen-containing cyclic nuclei in structures. Quinoline and its derivatives exhibit several biological functions, including antimicrobial, anticancer, antimalarial, anti-inflammatory, antihypertensive, and antiasthmatic effects. In addition, over a hundred quinoline-based drugs are available to treat a variety of disorders. Because of its biological importance, researchers developed one-pot synthetic methods employing effective acid/base catalysts (Lewis acids, Brønsted acids, and ionic liquids), reagents, and transition-metal-based catalysts. These methods have some downsides, including longer reaction times, harsher reaction conditions, creation of byproducts, costly catalysts, use of hazardous solvents, an unacceptable economic yield, and catalyst recovery. Researchers' focus has switched to creating environmentally friendly and effective methods for the synthesis of quinoline derivatives as a result of these methodologic shortcomings. Because of its special qualities, the use of nanocatalysts or nanocomposites offers an option for the effective synthesis of quinolines. This review focuses on the published research articles on nanocatalysts to synthesize substituted quinoline derivatives. This review covers all contributions until May 2024, focusing on quinoline ring building and mechanistic issues. With the aid of this review, we anticipate that synthetic chemists will be able to develop more effective methods of synthesizing quinolines.

Visible-Light Driven Synthesis of Vinyl Amines without Photocatalyst

We developed a visible-light-induced vinyl amination of activated alkenes using TMSN3 and CsF through EDA complex formation under an oxygen atmosphere. Without light, the EDA complex forms between activated alkene, CsF, and oxygen. Upon exposure to light, oxygen in the complex gets excited, initiating the HAT process. This method efficiently synthesizes vinyl-amine derivatives via a radical pathway, demonstrating good functional group tolerance and high yields in a short time. Further, the late-stage functionalization enables the synthesis of biologically active heterocycles.

CuI-Catalyzed Selenylation of Pyrrolo[2,1-a]isoquinolines and Other Electron-Rich Heteroarenes

We have established a mild CuI-catalyzed selenylation of pyrrolo[2,1-a]isoquinoline derivatives in the presence of mCPBA (m-chloroperoxybenzoic acid) at ambient temperature. Corresponding organoselenides have been prepared readily in 53-92% yields. This process can also be expanded to the modification of pyrroles, azaindole, and indoles, delivering the desired heterocyclic selenides in moderate to good yields.

Well-Defined Highly-Coordinated Copper(III) Iodide and Pincer Tris(trifluoromethyl)copper Complexes

Copper(III) iodide and bromide complexes representing a unique combination of highly-coordinated metal and soft polarizable anions were synthesized and fully characterized, including X-ray crystallography. Ligand substitution in well-defined highly-coordinated copper complex PyCu(CF3)3 with pincer ligands was achieved to give formally octahedral copper(III) complexes.

Expanding the Clip-and-Cleave Concept: Approaching Enantioselective C-H Hydroxylations by Copper Imine Complexes Using O2 and H2O2 as Oxidants

Copper-mediated aromatic and aliphatic C-H hydroxylations using benign oxidants (O2 and H2O2) have been studied intensively in recent years to meet the growing demand for efficient and green C-H functionalizations. Herein, we report an enantioselective variant of the so-called clip-and-cleave concept for intramolecular ligand hydroxylations by the application of chiral diamines as directing groups. We tested the hydroxylation of cyclohexanone and 1-acetyladamantane under different oxidative conditions (CuI/O2; CuI/H2O2; CuII/H2O2) in various solvents. As an outstanding example, we obtained (R)-1-acetyl-2-adamantol with a yield of 37% and >99:1 enantiomeric excess from hydroxylation in acetone using CuI and O2. Low-temperature stopped-flow UV-vis measurements in combination with density functional theory (DFT) computations revealed that the hydroxylation proceeds via a bis(μ-oxido) dicopper intermediate. The reaction product represents a rare example of an enantiopure 1,2-difunctionalized adamantane derivative, which paves the way for potential pharmacological studies. Furthermore, we found that 1-acetyladamantane can be hydroxylated in a one-pot reaction under air with isolated yields up to 36% and enantiomeric ratios of 96:4 using CuII/H2O2 in MeOH.

Aerobic Copper-Catalyzed Oxysulfonylation of Vinylarenes with Sodium Sulfinates under Mild Conditions: A Modular Synthesis of β-Ketosulfones

An aerobic copper-catalyzed oxysulfonylation of vinylarenes with sodium sulfinates is described. This protocol features mild reaction conditions, convenient operation, and broad substrate scope with respect to vinylarenes and sodium sulfinates. Notably, the protocol demonstrates excellent tolerance of functional groups such as chloro, bromo, ester, cyano, and nitro groups. Mechanistic investigations indicated that the reaction should undergo radical cascades involving a sulfonyl radical generated from sodium sulfinate with air as the terminal oxidant, addition across alkene to deliver a benzylic radical, and subsequent cross-coupling with air.

Dioxygenase Chemistry in Nucleophilic Aldehyde Deformylations Utilizing Dicopper O2-Derived Peroxide Complexes

The chemistry of copper-dioxygen complexes is relevant to copper enzymes in biology as well as in (ligand)Cu-O2 (or Cu2-O2) species utilized in oxidative transformations. For overall energy considerations, as applicable in chemical synthesis, it is beneficial to have an appropriate atom economy; both O-atoms of O2(g) are transferred to the product(s). However, examples of such dioxygenase-type chemistry are extremely rare or not well documented. Herein, we report on nucleophilic oxidative aldehyde deformylation reactivity by the peroxo-dicopper(II) species [Cu2II(BPMPO-)(O22-)]1+ {BPMPO-H = 2,6-bis{[(bis(2-pyridylmethyl)amino]methyl}-4-methylphenol)} and [Cu2II(XYLO-)(O22-)]1+ (XYLO- = a BPMPO- analogue possessing bis(2-{2-pyridyl}ethyl)amine chelating arms). Their dicopper(I) precursors are dioxygenase catalysts. The O2(g)-derived peroxo-dicopper(II) intermediates react rapidly with aldehydes like 2-phenylpropionaldehyde (2-PPA) and cyclohexanecarboxaldehyde (CCA) in 2-methyltetrahydrofuran at -90 °C. Warming to room temperature (RT) followed by workup results in good yields of formate (HC(O)O-) along with ketones (acetophenone or cyclohexanone). Mechanistic investigation shows that [Cu2II(BPMPO-)(O22-)]1+ species initially reacts reversibly with the aldehydes to form detectable dicopper(II) peroxyhemiacetal intermediates, for which optical titrations provide the Keq (at -90 °C) of 73.6 × 102 M-1 (2-PPA) and 10.4 × 102 M-1 (CCA). In the reaction of [Cu2II(XYLO-)(O22-)]1+ with 2-PPA, product complexes characterized by single-crystal X-ray crystallography are the anticipated dicopper(I) complex, [Cu2I(XYLO-)]1+ plus a mixed-valent Cu(I)Cu(II)-formate species. Formate was further identified and confirmed by 1H NMR spectroscopy and electrospray ionization mass spectrometry (ESI-MS) analysis. Using 18O2(g)-isotope labeling the reaction produced a high yield of 18-O incorporated acetophenone as well as formate. The overall results signify that true dioxygenase reactions have occurred, supported by a thorough mechanistic investigation.

CuBr2-mediated dehydrogenative [4+2] annulation of 1-naphthyl-1,3-indandiones and alkenes

Intermolecular annulation reactions of 1-naphthyl-1,3-indandiones with alkenes proceed efficiently in the presence of a copper catalyst to generate spirocarbocycle compounds. Various spirocyclic molecules bearing an all-carbon quaternary center could be obtained by this novel method with good yields, excellent regioselectivity, and good functional group tolerance. A radical mechanism is proposed based on the HRMS analysis results of control experiments.

A new strategy for immobilization of copper on the Fe3O4@EDTA nanocomposite and its efficient catalytic applications in reduction and one-pot reductive acetylation of nitroarenes and also N-acetylation of arylamines

A new and efficient Cu(II)-containing mesoporous nanocatalytic system was synthesized by direct immobilization of copper metal powder on the Fe3O4@EDTA nanocomposite. The as-prepared Fe3O4@EDTA@Cu(II) nanocomposite was then characterized by FT-IR, XRD, SEM, TEM, SEM-based EDX and elemental mapping, XPS, TGA, VSM, and also BET and BJH analyses. The resulting Fe3O4@EDTA@Cu(II) mesoporous nanocomposite exhibited satisfactory catalytic activity towards the reduction and one-pot reductive acetylation of nitroarenes and also N-acetylation of arylamines in water at 60 °C. Notably, the applied Cu(II)-containing nanocatalyst was efficiently recovered from the reaction mixture using an external magnetic field and could be reused successfully for five cycles. The protocol developed in this study offers several advantages in terms of mild reaction conditions, simple workflows, using water as a green solvent, and easy recovery and catalyst reuse, making it more ecologically and economically attractive.

Cu-Catalyzed Tandem Oxidation-Intramolecular Cannizzaro Reaction of Biorenewables and Bioactive Molecules

A tandem Cu-catalyzed oxidation-intramolecular Cannizzaro reaction leading to bioactive α-hydroxyesters from α-hydroxyketones is reported. The process uses oxygen as a sole oxidant to achieve the formation of glyoxals, which are efficiently converted in situ to important α-hydroxyesters. The mechanistic insights are provided by isotopic labeling and supported by DFT calculations. The transformation proved a robust synthetic tool to achieve the synthesis of human metabolites and hydroxyl esters of various biologically active steroid derivatives.

Biochemical Behavior, Influence on Cell DNA Condition, and Microbiological Properties of Wool and Wool-Copper Materials

The paper presents the study concerning the preparation and physio-chemical and biological properties of wool-copper (WO-Cu) materials obtained by the sputter deposition of copper onto the wool fibers. The WO-Cu material was subjected to physio-chemical and biological investigations. The physio-chemical investigations included the elemental analysis of materials (C, N, O, S, and Cu), their microscopic analysis, and surface properties analysis (specific surface area and total pore volume). The biological investigations consisted of the antimicrobial activity tests of the WO-Cu materials against colonies of Gram-positive (Staphylococcus aureus) bacteria, Gram-negative (Escherichia coli) bacteria, and fungal mold species (Chaetomium globosum). Biochemical-hematological tests included the evaluation of the activated partial thromboplastin time and pro-thrombin time. The tested wool-copper demonstrated the ability to interact with the DNA in a time-dependent manner. These interactions led to the DNA's breaking and degradation. The antimicrobial and antifungal activities of the WO-Cu materials suggest a potential application as an antibacterial/antifungal material. Wool-copper materials may be also used as customized materials where the blood coagulation process could be well controlled through the appropriate copper content.

Two-Dimensional Cu(II)-MOF with Lewis Acid-Base Bifunctional Sites for Chemical Fixation of CO2 and Bioactive 1,4-DHP Synthesis via Hantzsch Condensation

Five- and six-membered heterocycles containing nitrogen or oxygen have been considered as privileged scaffolds in organic chemistry and the chemical industry because of their usage in high-value commodities. Herein, we report a two-dimensional (2D) Cu(II)-based MOF catalyst, IITKGP-40, via the strategic employment of ample Lewis acid-base bifunctional sites (open metal nodes and free pyrazine moieties) along the pore wall. IITKGP-40 could convert toxic CO2 to cyclic carbonates in an atom-economical manner under solvent-free conditions and aromatic aldehyde to bioactive 1,4-DHPs via Hantzsch condensation. Exceptional catalytic performance (99%) and turnover number under mild reaction conditions for CO2 fixation using sterically hindered styrene oxide, and good-to-excellent yields for a wide range of aromatic aldehydes toward 1,4-dihydropyridines (1,4-DHPs) make IITKGP-40 promising as a multipurpose heterogeneous catalyst. Moreover, to demonstrate the practical utility of the catalyst, two biologically important drug molecules, diludine and nitrendipine analogue, have also been synthesized. IITKGP-40 is recyclable for at least three consecutive runs without significant loss of activity, making it promising for real-time applications.

Copper/O2-Mediated Oxidative C-C Activation of Nitriles for Selective Acylation-Bromination of Anilines

This study reports selective dual amino acylation and C-H bromination of aniline compounds enabled by Cu/O2 catalyst systems. This method involves crucial oxidation-induced C-CN bond cleavage of α-methylene nitriles to generate an acylcyanide intermediate that is facilely intercepted by anilines. After amino acylation, the Cu(II) precatalyst in combination with NBS generates Cu(III)-Br in situ that engages in selective electrophilic para- or ortho-C-H bromination. The substrate scope, mechanistic aspects, and late-stage functionalization of biologically active anilines are studied. This study shows the synthetic potential of oxidative C-CN bond activation of nitriles for the development of valuable reactions.

Coordination Variations within Binuclear Copper Dioxygen-Derived (Hydro)Peroxo and Superoxo Species; Influences upon Thermodynamic and Electronic Properties

Copper ion is a versatile and ubiquitous facilitator of redox chemical and biochemical processes. These include the binding of molecular oxygen to copper(I) complexes where it undergoes stepwise reduction-protonation. A detailed understanding of thermodynamic relationships between such reduced/protonated states is key to elucidate the fundamentals of the chemical/biochemical processes involved. The dicopper(I) complex [CuI2(BPMPO-)]1+ {BPMPOH = 2,6-bis{[(bis(2-pyridylmethyl)amino]methyl}-4-methylphenol)} undergoes cryogenic dioxygen addition; further manipulations in 2-methyltetrahydrofuran generate dicopper(II) peroxo [CuII2(BPMPO-)(O22-)]1+, hydroperoxo [CuII2(BPMPO-)(-OOH)]2+, and superoxo [CuII2(BPMPO-)(O2•-)]2+ species, characterized by UV-vis, resonance Raman and electron paramagnetic resonance (EPR) spectroscopies, and cold spray ionization mass spectrometry. An unexpected EPR spectrum for [CuII2(BPMPO-)(O2•-)]2+ is explained by the analysis of its exchange-coupled three-spin frustrated system and DFT calculations. A redox equilibrium, [CuII2(BPMPO-)(O22-)]1+ ⇄ [CuII2(BPMPO-)(O2•-)]2+, is established utilizing Me8Fc+/Cr(η6-C6H6)2, allowing for [CuII2(BPMPO-)(O2•-)]2+/[CuII2(BPMPO-)(O22-)]1+ reduction potential calculation, E°' = -0.44 ± 0.01 V vs Fc+/0, also confirmed by cryoelectrochemical measurements (E°' = -0.40 ± 0.01 V). 2,6-Lutidinium triflate addition to [CuII2(BPMPO-)(O22-)]1+ produces [CuII2(BPMPO-)(-OOH)]2+; using a phosphazene base, an acid-base equilibrium was achieved, pKa = 22.3 ± 0.7 for [CuII2(BPMPO-)(-OOH)]2+. The BDFEOO-H = 80.3 ± 1.2 kcal/mol, as calculated for [CuII2(BPMPO-)(-OOH)]2+; this is further substantiated by H atom abstraction from O-H substrates by [CuII2(BPMPO-)(O2•-)]2+ forming [CuII2(BPMPO-)(-OOH)]2+. In comparison to known analogues, the thermodynamic and spectroscopic properties of [CuII2(BPMPO-)] O2-derived adducts can be accounted for based on chelate ring size variations built into the BPMPO- framework and the resulting enhanced CuII-ion Lewis acidity.

Manganese-Catalyzed 5-Endo-trig Oxygenative Cyclization of α,β-Unsaturated Oximes under Air and Ambient Conditions for the Synthesis of 4,5-Dihydroisoxazoles

The stereoselective 5-endo-trig oxygenative cyclization of α,β-unsaturated oximes was achieved using molecular oxygen (O2) and a manganese catalyst. Several 4-hydroxy-4,5-dihydroisoxazoles were obtained in high yields by directly incorporating O2 from the atmosphere (eliminating the necessity for a pure oxygen environment) and using an unprecedentedly low loading of Mn(acac)3 (as little as 0.020 mol %) without additional additives. Because of its desirable features, such as operational simplicity, inexpensive catalyst, mild reaction conditions (open flask conditions at room temperature), and broad substrate compatibility, this novel reaction provides an attractive synthetic approach to producing 4-hydroxy-4,5-dihydroisoxazoles.

Recent Advances in Electrocatalytic Hydrogenation Reactions on Copper-Based Catalysts

Hydrogenation reactions play a critical role in the synthesis of value-added products within the chemical industry. Electrocatalytic hydrogenation (ECH) using water as the hydrogen source has emerged as an alternative to conventional thermocatalytic processes for sustainable and decentralized chemical synthesis under mild conditions. Among the various ECH catalysts, copper-based (Cu-based) nanomaterials are promising candidates due to their earth-abundance, unique electronic structure, versatility, and high activity/selectivity. Herein, recent advances in the application of Cu-based catalysts in ECH reactions for the upgrading of valuable chemicals are systematically analyzed. The unique properties of Cu-based catalysts in ECH are initially introduced, followed by design strategies to enhance their activity and selectivity. Then, typical ECH reactions on Cu-based catalysts are presented in detail, including carbon dioxide reduction for multicarbon generation, alkyne-to-alkene conversion, selective aldehyde conversion, ammonia production from nitrogen-containing substances, and amine production from organic nitrogen compounds. In these catalysts, the role of catalyst composition and nanostructures toward different products is focused. The co-hydrogenation of two substrates (e.g., CO2 and NOx n, SO3 2-, etc.) via C─N, C─S, and C─C cross-coupling reactions are also highlighted. Finally, the critical issues and future perspectives of Cu-catalyzed ECH are proposed to accelerate the rational development of next-generation catalysts.

Biomimetic Total Synthesis of Bimagnolignan: A Natural Anti-Breast Cancer Agent

A short scalable biomimetic route to bioactive natural product bimagnolignan (1) was accomplished. Compound 1 was successfully prepared through a three-step metal-free synthesis from honokiol (2). Alternatively, 1 was also synthesized by biomimetic transformations that mimic tyrosinase in four steps. The key reactions feature a regioselective acetylation, a highly efficient C(sp2)-H oxidation, a cascade aerobic oxidative cyclization/coupling, and a Cu-catalyzed direct oxidative coupling. In addition, cell-based assays validate that 1 is a promising natural lead for HER2-positive breast cancer treatment.

Development and synthesis of a novel salen-type ligand based on phenylalanine for Mizoroki-Heck, and S-arylation cross-coupling reactions

In this article, we introduced a novel salen-type ligand precursor and applied it in the Pd-catalyzed Mizoroki-Heck and Cu-catalyzed S-arylation cross-coupling reactions. For the preparation of this structure, (DL)-phenyl alanine was employed as a starting material. These ligand precursor and related catalytic system can be readily synthesised. Various aryl halides (-I, -Br) and alkenes were applied successfully in this protocol to give the corresponding Mizoroki-Heck cross-coupling and S-arylated products in high to excellent yields.

Label-free multimodal analysis of copper ions at below permissible exposure limit in the aqueous medium

An anthraimidazoledione based amphiphilic dye molecule was synthesized that shows formation of tuneable charge-transfer state in solution, susceptible to change in pH, polarity and hydrogen bonding ability of the medium. The compound also showed formation of nanoscopic self-assembled structure in water medium. The probe molecule can achieve multimodal detection (colorimetric, fluorimetric and electrochemical) of copper ions as low as 0.3 ppm in the aqueous medium. Addition of copper leads to dose-dependent ratiometric change in solution color from yellow to purple. The mechanistic investigation indicates that the coordination of copper ions was possible via simultaneous engagement of both imidazole nitrogen ends and neighbouring hydroxyl unit. Not only optical property, the changes in microenvironment also influence the selectivity as well as sensitivity of the probe molecule towards Cu2+ ions. Further, the optical probe is used for detection as well as quantification of copper ions in natural water samples without any sample pretreatment. Low-cost, reusable paper strips are developed for rapid, on-location detection of residual Cu2+ in real-life samples.

Dioxygen compatible electron donor-acceptor catalytic system and its enabled aerobic oxygenation

The photochemical properties of Electron Donor-Acceptor (EDA) complexes present exciting opportunities for synthetic chemistry. However, these strategies often require an inert atmosphere to maintain high efficiency. Herein, we develop an EDA complex photocatalytic system through rational design, which overcomes the oxygen-sensitive limitation of traditional EDA photocatalytic systems and enables aerobic oxygenation reactions through dioxygen activation. The mild oxidation system transfers electrons from the donor to the effective catalytic acceptor upon visible light irradiation, which are subsequently captured by molecular oxygen to form the superoxide radical ion, as demonstrated by the specific fluorescent probe, dihydroethidine (DHE). Furthermore, this visible-light mediated oxidative EDA protocol is successfully applied in the aerobic oxygenation of boronic acids. We believe that this photochemical dioxygen activation strategy enabled by EDA complex not only provides a practical approach to aerobic oxygenation but also promotes the design and application of EDA photocatalysis under ambient conditions.

Aerobic Catalytic Cross-Dehydrogenative Coupling of Furans with Indoles Provides Access to Fluorophores with Large Stokes Shift

Sustainability in chemical processes is a crucial aspect in contemporary chemistry with sustainable catalysis as a vital parameter of the same. There has been a renewed focus on utilizing earth-abundant metal catalysts to expand the repertoire of organic reactions. Furan is a versatile heterocycle of natural origin used for multiple applications. However, it has scarcely been used in cross-dehydrogenative coupling. In this work, we have explored the cross-dehydrogentive coupling of furans with indoles using commonly available, inexpensive FeCl3  ⋅ 6H2 O (<0.25 $/g) as catalyst in the presence of so called 'ultimate oxidant' - oxygen, without the need for any external ligand or additive. The reactions were found to be scalable and to work even under partially aqueous conditions. This makes the reaction highly economical, practical, operationally simple and sustainable. The methodology provides direct access to π-conjugated short oligomers consisting of furan, thiophene and indole. These compounds were found to show interesting fluorescence properties with remarkably large Stokes shift (up to 205 nm). Mechanistic investigations reveal that the reaction proceeds through chemoselective oxidation of indole by the metal catalyst followed by nucleophilic trapping by furan.

Oxygenation of Phenols with Water as the Oxygen Source and Oxoammonium Salt as the Oxidant

Aromatic C-H oxygenation is important in both industrial production and organic synthesis. Here we report a metal-free approach for phenol oxygenation with water as the oxygen source using oxoammonium salts as the renewable oxidant. Employing this protocol, various alkyl-substituted phenols were converted into benzoquinones in yields of 59-98%. On the basis of 18O-labeling and kinetic studies, the hydroxy-oxoammonium adduct was proposed to attack the aromatic ring similarly to electrophilic aromatic substitution. We suppose that the findings described here not only provide an efficient and highly selective protocol for aromatic C-H oxygenation but also may encourage further developments of possible transition-metal-free catalytic methods.

Divergent Bimetallic Mechanisms in Copper(II)-Mediated C-C, N-N, and O-O Oxidative Coupling Reactions

Copper-catalyzed aerobic oxidative coupling of diaryl imines provides a route for conversion of ammonia to hydrazine. The present study uses experimental and density functional theory computational methods to investigate the mechanism of N-N bond formation, and the data support a mechanism involving bimolecular coupling of Cu-coordinated iminyl radicals. Computational analysis is extended to CuII-mediated C-C, N-N, and O-O coupling reactions involved in the formation of cyanogen (NC-CN) from HCN, 1,3-butadiyne from ethyne (i.e., Glaser coupling), hydrazine from ammonia, and hydrogen peroxide from water. The results reveal two different mechanistic pathways. Heteroatom ligands with an uncoordinated lone pair (iminyl, NH2, OH) undergo charge transfer to CuII, generating ligand-centered radicals that undergo facile bimolecular radical-radical coupling. Ligands lacking a lone pair (CN and CCH) form bridged binuclear diamond-core structures that undergo C-C coupling. This mechanistic bifurcation is rationalized by analysis of spin densities in key intermediates and transition states, as well as multiconfigurational calculations. Radical-radical coupling is especially favorable for N-N coupling owing to energetically favorable charge transfer in the intermediate and thermodynamically favorable product formation.

Aminoquinoline-Based Tridentate (NNN)-Copper Catalyst for C-N Bond-Forming Reactions from Aniline and Diazo Compounds

A new tridentate Cu2+ complex based on (E)-1-(pyridin-2-yl)-N-(quinolin-8-yl)methanimine (PQM) was generated and characterized to support the activation of diazo compounds for the formation of new C-N bonds. This neutral Schiff base ligand was structurally characterized to coordinate with copper(II) in an equatorial fashion, yielding a distorted octahedral complex. Upon characterization, this copper(II) complex was used to catalyze an efficient and cost-effective protocol for C-N bond formation between N-nucleophiles and copper carbene complexes arising from the activation of diazo carbonyl compounds. A substrate scope of approximately 15 different amine-based substrates was screened, yielding 2° or 3° amine products with acceptable to good yields under mild reaction conditions. Reactivity towards phenol and thiophenol were also screened, showing relatively weak C-O or C-S bond formation under optimized conditions.

CuI/DMAP-Catalyzed Oxidative Alkynylation of 7-Azaindoles: Synthetic Scope and Mechanistic Studies

An efficient and practical method for the N-alkynylation of 7-azaindoles has been established by using CuI/DMAP catalytic system at room temperature and in open air. This simple protocol has been successfully employed in the synthesis of a wide range of N-alkynylated 7-azaindoles with good yields. Also, this approach is well-suited for large-scale N-alkynylation reactions. The designed N-alkynylated 7-azaindoles were further subjected to Cu-/Ir-catalyzed alkyne-azide cycloaddition (CuAAC/IrAAC) or "click" reaction for the rapid synthesis of 1,4-/1,5 disubstituted 1,2,3-triazole decorated 7-azaindoles. A mechanistic study based on density functional theory (DFT) calculations and ultraviolet-visible (UV) spectroscopic studies revealed that the CuI and DMAP combination formed a [CuII (DMAP)2 I2 ] species, which acts as an active catalyst. The DFT method was used to assess the energetic viability of an organometallic in the C-N bond formation pathway originating from the [CuII (DMAP)2 I2 ] complex. We expect that the newly designed Cu/DMAP/alkyne system will offer valuable insights into the field of Cu-catalyzed transformations.

Design of luminescent complexes with different Cu4I4 cores based on pyridyl phenoxarsines

A series of luminescent Cu4I4 clusters with stair-step, cubane, and octahedral geometries supported by a novel type of cyclic As,N-ligand, pyridyl-containing 10-phenoxarsines, were synthesized and characterized by NMR spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray diffraction analysis. An unusual arrangement of As,N-bidentate and μ2-iodo ligands was found in the octahedral cluster. The structural diversity of the Cu(I) complexes is reflected in their photophysical properties: the phosphorescence spectra of the compounds display emission in a broad spectral range of 495-597 nm. The complex with the Cu4I4L2 stoichiometry bearing a stair-step Cu4I4 core demonstrates temperature-dependent dual emission. The luminescence properties of all complexes were rationalized by DFT calculations.

Catalytic Synthesis of Silanols by Hydroxylation of Hydrosilanes: From Chemoselectivity to Enantioselectivity

As a crucial class of functional molecules in organosilicon chemistry, silanols are found valuable applications in the fields of modern science and will be a potentially powerful framework for biologically active compounds or functional materials. It has witnessed an increasing demand for non-natural organosilanols, as well as the progress in the synthesis of these structural features. From the classic preparative methods to the catalytic selective oxidation of hydrosilanes, electrochemical hydrolysis of hydrosilanes, and then the construction of the most challenging silicon-stereogenic silanols. This review summarized the progress in the catalyzed synthesis of silanols via hydroxylation of hydrosilanes in the last decade, with a particular emphasis on the latest elegant developments in the desymmetrization strategy for the enantioselective synthesis of silicon-stereogenic silanols from dihydrosilanes.

Palladium-based pseudohomogeneous catalyst for highly selective aerobic oxidation of benzylic alcohols to aldehydes

This study presents a novel class of pseudohomogeneous catalysts (PHC) based on carbon quantum dots functionalized with terpyridine ligands (CQDs-Tpy) to immobilize and stabilize palladium nanoparticles (Pd NPs). Extensive characterization techniques clearly confirmed the successful stabilization of Pd NPs on CQDs-Tpy. The effectiveness of the catalyst was demonstrated in the selective aerobic oxidation of primary and secondary of benzylic alcohols to aldehydes in the absence of additives and phase transfer catalyst (PTC). Remarkably, the reactions predominantly yielded aldehydes without further oxidation to carboxylic acids. By employing low catalyst loadings (0.13 mol%), high conversions (up to 89%) and excellent selectivity (> 99%) of the aldehyde derivatives were achieved. Moreover, the CQDs-Tpy/Pd NPs catalyst displayed suitable catalytic activity and recyclability, offering potential economic advantages. This promising approach opens up new opportunities in the field of catalysis for designing subnanometric metal-based PHCs.

Cu(ii)-catalyzed aerobic oxidative coupling of furans with indoles enables expeditious synthesis of indolyl-furans with blue fluorescence

With the purpose of incorporating sustainability in chemical processes, there has been a renewed focus on utilizing earth-abundant metal catalysts to expand the repertoire of organic reactions and processes. In this work, we have explored the atom-economic oxidative coupling between two important electron-rich heterocycles - indoles and furans - using commonly available, inexpensive metal catalyst CuCl2·2H2O (<0.25$ per g) to develop an expeditious synthesis of indolyl-furans. Moreover, the reaction proceeded well in the presence of the so-called 'ultimate oxidant' - air, without the need for any external ligand or additive. The reaction was found to be scalable and to work even under partially aqueous conditions. This makes the methodology highly economical, practical, operationally simple and sustainable. In addition, the methodology provides direct access to novel indole-furan-thiophene (IFT)-based electron-rich π-conjugated systems, which show green-yellow fluorescence with large Stokes shift and high quantum yields. Mechanistic investigations reveal that the reaction proceeds through chemoselective oxidation of indole by the metal catalyst followed by the nucleophilic attack by furan.

Transition-Metal-Catalyzed 1,2-Diaminations of Olefins: Synthetic Methodologies and Mechanistic Studies

1,2-Diamines are synthetically important motifs in organo-catalysis, natural products, and drug research. Continuous utilization of transition-metal based catalyst in direct 1,2-diamination of olefines, in contrast to metal-free transformations, with numerous impressive advances made in recent years (2015-2023). This review summarized contemporary research on the transition-metal catalyzed/mediated [e. g., Cu(II), Pd(II), Fe(II), Rh(III), Ir(III), and Co(II)] 1,2-diamination (asymmetric and non-asymmetric) especially emphasizing the recent synthetic methodologies and mechanistic understandings. Moreover, up-to-date discussion on (i) paramount role of oxidant and catalyst (ii) key achievements (iii) generality and uniqueness, (iv) synthetic limitations or future challenges, and (v) future opportunities are summarized related to this potential area.

Copper in Cancer: from transition metal to potential target

In recent years, with the continuous in-depth exploration of the molecular mechanisms of tumorigenesis, numerous potential new targets for cancer treatment have been identified, some of which have been further developed in clinical practice and have produced positive outcomes. Notably, researchers' initial motivation for studying copper metabolism in cancer stems from the fact that copper is a necessary trace element for organisms and is closely connected to body growth and metabolism. Moreover, over the past few decades, considerable progress has been made in understanding the molecular processes and correlations between copper and cancer. Certain achievements have been made in the development and use of relevant clinical medications. The concept of "cuproptosis," a novel concept that differs from previous forms of cell death, was first proposed by a group of scientists last year, offering fresh perspectives on the targeting capabilities of copper in the treatment of cancer. In this review, we introduced the fundamental physiological functions of copper, the key components of copper metabolism, and a summary of the current research contributions on the connection between copper and cancer. In addition, the development of new copper-based nanomaterials and their associated mechanisms of action are discussed. Finally, we described how the susceptibility of cancer cells to this metallic nutrition could be leveraged to further improve the existing cancer treatment paradigm in the new setting.

Recent advances in computational studies on Cu-catalyzed aerobic reactions: cooperation of copper catalysts and dioxygen

O2, one of the ideal oxidants, suffers from low solubility, low oxidizability, low selectivity and a triplet ground state when applied in organic synthesis. Biomimetic copper catalysis has been demonstrated to be a powerful method for activating and transforming O2 to conduct aerobic reactions for a long time. On the other hand, the structures of Cu-O2 complexes are complex with diverse downstream reactions, whereas active copper intermediates were rarely identified by experimental methods, making the mechanisms of many Cu-catalyzed aerobic reactions far from clear. In this context, computational studies emerged as an effective alternative to mechanistic studies on Cu-catalyzed aerobic reactions. This review introduces the relevant computational studies since 2012, focusing on showing the cooperation of copper catalysts and O2 in dehydrogenation, oxygenation and coupling reactions.

Modular Synthesis of α-Aryl-α-Heteroaryl α-Amino Acid Derivatives via a Copper-Catalyzed Cross-Dehydrogenative-Coupling Reaction Using Air as the Sole Oxidant

A novel copper-catalyzed cross-dehydrogenative-coupling (CDC) process of arylglycine derivatives with N-heteroarenes for the straightforward synthesis of α-aryl-α-heteroaryl α-amino acid scaffolds has been successfully developed. This protocol exhibits a broad substrate scope with good functional group compatibility by utilizing air as the sole oxidant. The use of the reaction is also displayed through the late-stage functionalization of arylglycines bearing natural compounds or drug motifs.

Comproportionation and disproportionation in nickel and copper complexes

Disproportionation and comproportionation reactions have become increasingly important electron transfer events in organometallic chemistry and catalysis. The renewed interest in these reactions is in part attributed to the improved understanding of first-row metals and their ability to occupy odd and even oxidation states. Disproportionation and comproportionation reactions enable metal complexes to shuttle between various oxidation states, a matter of utmost relevance for controlling the speciation and catalytic turnover. In addition, these reactions have a direct impact in the thermodynamic and kinetic stability of the corresponding metal complexes. This review covers the relevance and impact of these processes in electron transfer reactions and provides valuable information about their non-negligible influence in Ni- and Cu-catalysed transformations.

Deciphering the effect of amine versus imine ligands of copper(II) complexes in 2-aminophenol oxidation

A series of amine (1-6) and imine (5',6') based copper(II) complexes with tridentate (NNO) ligand donors were synthesized and characterized using modern analytical techniques. All the complexes were subjected to 2-aminophenol (OAP) oxidation to form 2-aminophenoxazin-3-one, as a functional analogue of an enzyme, phenoxazinone synthase. In addition, a critical comparison of the reactivity using the amine-based complexes with their respective imine counterparts was achieved in both experimental as well as theoretical studies. For instance, the kinetic measurement revealed that the imine-based copper(II) complexes (kcat, 2.4 × 105-6.2 × 106 h-1) are better than amine-based (kcat, 6.3 × 104-3.9 × 105 h-1) complexes. The complex-substrate adducts [Cu(L3)(OAP)] (7) and [Cu(L3')(OAP)] (7') were characterized for both systems by mass spectrometry. Further, the DFT study was performed with amine- (3) and imine- (3') based copper(II) complexes, to compare their efficacy in the oxidation of OAP. The mechanistic investigations reveal that the key elementary step to determine the reactivity of 3 and 3' is the proton-coupled electron transfer (PCET) step occurring from the intermediates 7/7'. Further, the computed HOMO-LUMO energy gap of 7' was smaller than 7 by 0.8 eV, which indicates the facile PCET compared to that of 7. Moreover, the coupling of the OAP moiety using imine-complexes (ΔGR.E = -5.8 kcal/mol) was found to be thermodynamically more favorable than amine complexes (ΔGR.E = +3.3 kcal/mol). Overall, the theoretical findings are in good agreement with the experimental results.

Catalytic cascade synthesis of cyanohydrin esters via water/O2-induced cyanide transfer from K3Fe(CN)6

The copper-catalyzed α-oxygenation of aryl benzyl ketones is merged with a unique water/O2-induced release of cyanide ions from K3Fe(CN)6 and a benzil-cyanide reaction. This strategy gives expedient access to cyanohydrin esters starting directly from broadly accessible aryl benzyl ketones. The cyanide release strategy was further integrated with a copper catalyzed oxygenation-decarbonylation sequence to produce cyanohydrin esters from 1,3-diketones.

Fixing CO2 under Atmospheric Conditions and Dual Functional Heterogeneous Catalysis Employing Cu MOFs: Polymorphism, Single-Crystal-to-Single-Crystal (SCSC) Transformation and Magnetic Studies

New copper compounds, [Cu(C14H8O6)(C10H8N2)(H2O)] (1), [Cu(C14H8O6)(C10H8N2)(H2O)]·(C3H7ON)2 (2), [Cu(C14H8O6)(C10H8N2)(H2O)2]·(C3H7ON) (3), [Cu(C14H8O6)(C10H8N4)] (4), and [Cu(C14H8O6)(C10H8N4)]·(H2O) (5), were prepared employing 2,5-bis(prop-2-yn-1-yloxy)terephthalic acid (2,5-BPTA) as the primary ligand and 4,4'-bipyridine (1-3) and 4,4'-azopyridine (4-5) as the secondary ligands. Single-crystal studies indicated that compounds 1-4 have two-dimensional layer structures and compound 5 has a three-dimensional structure. Compounds 1-3 were isolated from the same reaction mixture but by varying the time of reaction. The framework structures of compounds 1-3 are similar and may be considered as polymorphic structures. Compounds 4 and 5 can also be considered polymorphic with a change in dimensionality of the structure. Compounds 1-3 can be formed through a single-crystal-to-single-crystal transformation under a suitable solvent mixture. The Cu center was explored for the Lewis acid-catalyzed cycloaddition reaction of epoxide and CO2 under ambient conditions in a solventless condition and also for the synthesis of propargylamine derivatives by three-component coupling reactions (A3 coupling) in a DCM medium. The Lewis basic functionality of the MOF (-N═N- group) has been explored for the Henry reaction (aldol condensation) in a solventless condition. In all of the catalytic reactions, good yields and recyclability were observed. The magnetic studies indicated that compounds 1 and 4 have antiferromagnetic interactions and compound 5 has ferromagnetic interactions. The present studies illustrated the rich diversity that the copper-containing compounds exhibit in extended framework structures.

Methodological Development and Applications of Tryptamine-Ynamide Cyclizations in Synthesizing Core Skeletons of Indole Alkaloids

Over the past two decades, synthetic strategies for synthesizing the skeletons of various indole alkaloids based on tryptamine-ynamide have been continuously developed and applied to the total syntheses or formal total syntheses of related molecules. In this synopsis, we summarized the cyclization pathways of tryptamine-ynamide under different catalytic conditions, emphasizing the reaction mechanism and applications in the syntheses of indole alkaloids.

Electrochemical Oxidation of Δ9-Tetrahydrocannabinol at Nanomolar Concentrations

With increasing marijuana legalization, there is a growing need for technology that can determine if an individual is impaired due to recent marijuana usage. The electrochemical oxidation of Δ9-THC to form its corresponding quinones can be used as a framework to develop an electrochemical sensor for Δ9-THC. This study describes an electrochemical oxidation of Δ9-THC that uses a copper anode, a platinum cathode, and an atmosphere of oxygen. The oxidation is feasible at nanomolar concentrations, which approaches the reactivity that is necessary for developing a real-world marijuana breathalyzer. Moreover, we show that vaporized Δ9-THC can be captured directly in an electrolyte medium and subjected to electrochemical oxidation, thus paving the way for use in future technology development.

Advances in Selected Heterocyclization Methods

This Account summarizes efforts in our group toward synthesis of heterocycles in the past decade. Selected examples of transannulative heterocyclizations, intermediate construction of reactive compounds en route to these important motifs, and newer developments of a radical approach are outlined.

Water-Soluble Nanocomposites Containing Co3O4 Nanoparticles Incorporated in Poly-1-vinyl-1,2,4-triazole

New water-soluble nanocomposites with cobalt oxide nanoparticles (Co₃O₄NPs) in a poly(1-vinyl-1,2,4-triazole) (PVT) matrix have been synthesized. The PVT used as a stabilizing polymer matrix was obtained by radical polymerization of 1-vinyl-1,2,4-triazole (VT). The polymer nanocomposites with Co₃O₄ nanoparticles were characterized by ultraviolet-visible, Fourier-transform infrared spectroscopy, atomic absorption spectroscopy, transmission electron microscopy, dynamic light scattering, gel permeation chromatography, and simultaneous thermogravimetric analysis. The resulting polymer nanocomposites consist of spherical isolated cobalt nanoparticles with a diameter of 1 to 13 nm. The average hydrodynamic diameters of macromolecular coils are 15-112 nm. The cobalt content in nanocomposites ranges from 1.5 to 11.0 wt.%. The thermal stability of nanocomposites is up to 320 °C.

Reusable nano-catalyzed green protocols for the synthesis of quinoxalines: an overview

Heterocyclic compounds are very widely distributed in nature and are essential for life activities. They play a vital role in the metabolism of all living cells, for example, vitamins and co-enzyme precursors thiamine, riboflavin etc. Quinoxalines are a class of N-heterocycles that are present in a variety of natural and synthetic compounds. The distinct pharmacological activities of quinoxalines have attracted medicinal chemists considerably over the past few decades. Quinoxaline-based compounds possess extensive potential applications as medicinal drugs, presently; more than fifteen drugs are available for the treatment of different diseases. Diverse synthetic protocols have been developed via a one-pot approach using efficient catalysts, reagents, and nano-composites/nanocatalysts etc. But the use of homogeneous and transition metal-based catalysts suffers some demerits such as low atom economy, recovery of catalysts, harsh reaction conditions, extended reaction period, expensive catalysts, the formation of by-products, and unsatisfactory yield of products as well as toxic solvents. These drawbacks have shifted the attention of chemists/researchers to develop green and efficient protocols for synthesizing quinoxaline derivatives. In this context, many efficient methods have been developed for the synthesis of quinoxalines using nanocatalysts or nanostructures. In this review, we have summarized the recent progress (till 2023) in the nano-catalyzed synthesis of quinoxalines using condensation of o-phenylenediamine with diketone/other reagents with plausible mechanistic details. With this review, we hope that some more efficient ways of synthesizing quinoxalines can be developed by synthetic chemists.

CuII-Catalyzed cis-Selective Synthesis of Ketoepoxides from Phenacyl Bromides and Water

A verity of α,β-ketoepoxides was synthesized using a Cu^II-catalyzed oxidative C-C/O-C coupled cyclization strategy with high yield and cis-selectivity. Water is used as the source of oxygen and phenacyl bromide as the carbon in the valuable epoxides. The self-coupling method was extended to cross-coupling between phenacyl bromides with benzyl bromides. A high cis-diastereoselectivity was observed in all the synthesized ketoepoxides. Control experiments and density functional theory (DFT) study were performed to understand the Cu^II-Cu^I transition mechanism.

Copper-Catalyzed Enantioselective Aerobic Alkene Aminooxygenation and Dioxygenation: Access to 2-Formyl Saturated Heterocycles and Unnatural Proline Derivatives

Alkene aminooxygenation and dioxygenation reactions that result in carbonyl products are uncommon, and protocols that control absolute stereochemistry are rare. We report herein catalytic enantioselective alkene aminooxygenation and dioxygenation that directly provide enantioenriched 2-formyl saturated heterocycles under aerobic conditions. Cyclization of substituted 4-pentenylsulfonamides, catalyzed by readily available chiral copper complexes and employing molecular oxygen as both oxygen source and stoichiometric oxidant, directly provides chiral 2-formyl pyrrolidines efficiently. Reductive or oxidative workup of these aldehydes provides their respective amino alcohols or amino acids (unnatural prolines). Enantioselective synthesis of an indoline and isoquinolines is also demonstrated. Concurrently, cyclization of various alkenols under similar conditions provides 2-formyl tetrahydrofurans, phthalans, isochromans, and morpholines. The nature of the copper ligands, the concentration of molecular oxygen, and the reaction temperature all impact the product distribution. Chiral nitrogen and oxygen heterocycles are common components of bioactive small molecules, and these enabling technologies provide access to saturated heterocycles functionalized with ready-to-use carbonyl electrophiles.

Synthesis, Characterization, DNA/HSA Interaction, and Cytotoxic Activity of a Copper(II) Thiolate Schiff Base Complex and Its Corresponding Water-Soluble Stable Sulfinato-O Complex Containing Imidazole as a Co-ligand

A Cu(II) thiolato complex [CuL(imz)] (1) (H₂L = o-HOC₆H₄C(H)=NC₆H₄SH-o) and the corresponding water-soluble stable sulfinato-O complex [CuL'(imz)] (2) (H₂L' = o-HOC₆H₄C(H)=NC₆H₄S(=O)OH) were synthesized and characterized using physicochemical techniques. Compound 2 is found to be a dimer in the solid state as characterized using single-crystal X-ray crystallography. XPS studies clearly showed the differences in the sulfur oxidation states in 1 and 2. Both compounds are found to be monomers in solution as revealed from their four-line X-band electron paramagnetic resonance spectra in CH₃CN at room temperature (RT). 1-2 were tested to assess their ability to exhibit DNA binding and cleavage activity. Spectroscopic studies and viscosity experiments suggest that 1-2 bind to CT-DNA through the intercalation mode having moderate binding affinity (K_b ∼ 10⁴ M^-1). This is further supported by molecular docking studies of complex 2 with CT-DNA. Both complexes display significant oxidative cleavage of pUC19 DNA. Complex 2 also showed hydrolytic DNA cleavage. The interaction of 1-2 with HSA revealed that they have strong ability to quench the intrinsic fluorescence of HSA by a static quenching mechanism (k_q ∼ 10¹³ M^-1 s^-1). This is further complemented by Förster resonance energy transfer studies that revealed binding distances of r = 2.85 and 2.75 nm for 1 and 2, respectively, indicating high potential for energy transfer from HSA to complex. 1-2 were capable of inducing conformational changes of HSA at secondary and tertiary levels as observed from synchronous and three-dimensional fluorescence spectroscopy. Molecular docking studies with 2 indicate that it forms strong hydrogen bonds with Gln221 and Arg222 located near the entrance of site-I of HSA. 1-2 showed potential toxicity in human cervical cancer HeLa cells, lung cancer A549 cells, and cisplatin-resistant breast cancer MDA-MB-231 cells and appeared to be most potent against HeLa cells (IC₅₀ = 2.04 μM for 1 and 1.86 μM for 2). In HeLa cells, 1-2 mediated cell cycle arrest in S and G2/M phases, which progressed into apoptosis. Apoptotic features seen from Hoechst and AO/PI staining, damaged cytoskeleton actin viewed from phalloidin staining, and increased caspase-3 activity upon treatment with 1-2 collectively suggested that they induced apoptosis in HeLa cells via caspase activation. This is further supported by western blot analysis of the protein sample extracted from HeLa cells treated with 2.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects

This review provides recent developments in the current status and latest synthetic methodologies of biphenyl derivatives. Furthermore, this review investigates detailed discussions of several metalated chemical reactions related to biphenyl scaffolds such as Wurtz-Fittig, Ullmann, Bennett-Turner, Negishi, Kumada, Stille, Suzuki-Miyaura, Friedel-Crafts, cyanation, amination, and various electrophilic substitution reactions supported by their mechanistic pathways. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed. Furthermore, atropisomerism as a type of axial chirality in biphenyl molecules is discussed. Additionally, this review covers a wide range of biological and medicinal applications of the synthesized compounds involving patented approaches in the last decade corresponding to investigating the crucial role of the biphenyl structures in APIs.

Heterogeneous M-N-C Catalysts for Aerobic Oxidation Reactions: Lessons from Oxygen Reduction Electrocatalysts

Nonprecious metal heterogeneous catalysts composed of first-row transition metals incorporated into nitrogen-doped carbon matrices (M-N-Cs) have been studied for decades as leading alternatives to Pt for the electrocatalytic O2 reduction reaction (ORR). More recently, similar M-N-C catalysts have been shown to catalyze the aerobic oxidation of organic molecules. This Focus Review highlights mechanistic similarities and distinctions between these two reaction classes and then surveys the aerobic oxidation reactions catalyzed by M-N-Cs. As the active-site structures and kinetic properties of M-N-C aerobic oxidation catalysts have not been extensively studied, the array of tools and methods used to characterize ORR catalysts are presented with the goal of supporting further advances in the field of aerobic oxidation.

Mesoporous Copper-Magnesium Oxide Hybrid Nanocatalyzed Synthesis of 3-Substituted Isocoumarins from 2-Iodobenzoic Acid and Terminal Alkyne under Green Conditions

A 3-substituted isocoumarin scaffold has captivated extensive interest in synthetic and medicinal chemistry due to its presence in various natural products with diverse biological activities. Herein, we report a mesoporous CuO@MgO nanocomposite that was prepared via the sugar-blowing induced confined method with an E-factor of 12.2 and its catalytic potential in the facile synthesis of 3-substituted isocoumarin from 2-iodobenzoic acids and terminal alkynes. Powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller techniques were utilized for the characterization of the as-prepared nanocomposite. A broad substrate scope, mild reaction conditions, excellent yield in short reaction time, no usage of additives, and better green chemistry metrices such as a low E-factor (0.71), high reaction mass efficiency (58.28%), low process mass efficiency (1.71), and high turnover number (629) are the various advantages of the present synthetic route. The nanocatalyst was recycled and reused up to five runs without significant loss in its catalytic activity and a very low leaching of copper (3.20 ppm) and magnesium ions (0.72 ppm). Powder X-ray diffraction and high-resolution transmission electron microscopy techniques confirmed the structural integrity of the recycled CuO@MgO nanocomposite.