Application of Palladium-Catalyzed C(sp2)–H Bond Arylation to the Synthesis of Polycyclic (Hetero)Aromatics

Synthesis of zwitterionic open-shell bilayer spironanographenes

Molecular nanographenes (NGs) are nanoscale graphene fragments obtained by organic synthetic protocols. Here we report the bottom-up synthesis of two spiro-NGs formed by two substituted hexa-peri-hexabenzocoronenes (HBCs), spiro-NG and F-spiro-NG. The X-ray crystal structure of the deca-tert-butyl-functionalized spiro-NG shows a bilayer disposition of the HBCs in face-to-face contact. By contrast, F-spiro-NG, which features tert-butyl substituents on one HBC unit, and fluorine on the other HBC unit, is an electron donor-acceptor bilayer NG. The structural assembly of the donor and acceptor graphenic layers enables an electron-transfer process that leads to the formation of a zwitterionic open shell, paramagnetic species constituted by a radical cation and a radical anion located in the donor and the acceptor HBCs, respectively. Magnetic and spectroelectrochemical experiments, together with theoretical calculations, support the persistent/dominant charge-separated nature of F-spiro-NG. Furthermore, photoconductivity measurements show a significant increase of the charge carrier mobility in the case of F-spiro-NG (Σμ = 6 cm2 V-1 s-1) compared with spiro-NG.

Thiophene-backbone arcuate graphene nanoribbons: shotgun synthesis and length dependent properties

Efficient synthetic methods are urgently needed to produce graphene nanoribbons (GNRs) with diverse structures and functions. Precise control over the topological edges of GNRs is also crucial for achieving diverse molecular topologies and desirable electro-optical properties. This study demonstrates a highly efficient "shotgun" synthesis of thiophene-backbone arcuate GNRs, offering a significant advantage over tedious iterative synthesis. This method utilizes a one-pot, three component Suzuki-Miyaura coupling for the precursor, followed by a Scholl reaction for cyclization. The resulting arcuate GNRs have sulfur atoms embedded in the carbon backbone with a combined armchair, cove, and fjord edge structure. This multi-edge architecture is further modified by high-yield oxidation of the electron-rich sulfur atoms to electron-deficient sulfones, enabling precise regulation of the GNRs' electronic properties. These arcuate GNRs with diverse edge structures, heteroatom doping and precise lengths open exciting avenues for their application in optoelectronic devices.

Buckybowl-Based Nanocarbons: Synthesis, Properties, and Applications

ConspectusThe introduction of a five-membered ring into hexagon-fused networks typically induces strain that causes positive Gaussian curvature, leading to bowl-shaped polycyclic aromatic hydrocarbons (PAHs), often referred to as buckybowls or π-bowls. The interest in buckybowls is derived from their intriguing properties including, but not limited to, pyramidalized sp2 carbon atoms, low-lying lowest unoccupied molecular orbital (LUMO), surface charge stabilization, and bowl-to-bowl inversion. In recent years, investigations into the functionalization of buckybowls, as well as the structural aspects related to properties, have made significant progress. Indeed, the functionalization of buckybowls is a major route to increase structural diversity and fine-tune their properties. In particular, the fusion of aromatic rings to buckybowl rims (π-extension of buckybowls) has established a particularly promising synthetic strategy to access a wide range of buckybowl-based nanostructures with unique topologies and properties. A major obstacle, however, is the limited number of appropriate buckybowls, which could be suggested as potential frameworks for further functionalization. Moreover, buckybowls have been typically synthesized by ring-closing reactions, but many of these procedures suffer from the occurrence of considerable strain and lead to an undesired rearrangement. As a result, the development of buckybowl-based nanocarbons with desirable properties is still in its infancy due to the limited structural diversity, functionalization, and scalability.This Account describes our recent progress in the synthesis of buckybowls and buckybowl-based nanocarbons. In our study, diindeno[4,3,2,1-fghi:4',3',2',1'-opqr]perylene (DIP), pyracyleno[6,5,4,3,2,1-pqrstuv]pentaphene (PP), tetracyclopenta[cd,fg,jk,mn]pyrene (TPP), and corannulene are employed as basic structural units, which exhibit a bowl-shaped geometry and offer an ideal platform for functionalization. General bottom-up approaches have been used to access buckybowl derivatives functionalized with peripheral alkynyl and aryl groups. These substituent groups significantly influence solubility, energy levels, and crystal packing, all of which impact their performance. These buckybowls are ultimately converted into π-extended nanocarbons with wide-ranging structural diversity, including doubly curved, rippled, and chiral nanocarbons. Chiral buckybowl-based nanocarbons, where chirality is introduced from quasi-[8]circulene moieties, have high enantiomerization barriers, enabling the separation of the enantiomers. Notably, the rippled nanocarbon containing 10 aromatic rings directly fused to the TPP core exhibits attractive electronic, magnetic, and mechanical properties, which can be further functionalized through the use of well-established chemistry, opening up many possibilities to access unusual carbon allotropes.The assembly with fullerenes is an important application for buckybowls and buckybowl-based nanocarbons. Depending on the peripheral substituent, the binding constant of buckybowls with fullerenes can be tuned. Moreover, buckybowl-based nanocarbons significantly increase the ability to bind fullerenes, resulting in the formation of highly ordered host-guest systems. These features make the nanocarbons excellent molecules for device applications. As expected, these buckybowl-based nanocarbons can function as organic semiconductors for organic field-effect transistors (OFETs), which have mobilities up to 2.30 cm2 V-1 s-1. The host-guest complexes exhibit highly efficient ambipolar characteristics with nearly balanced mobilities on the order of 10-1 cm2 V-1 s-1. In addition, some buckybowl-based nanocarbons show promising applications in photothermal materials with over 90% photothermal conversion efficiency.

Twofold 6π-Electrocyclization as a Route Toward Multi-Heteroatom-Doped Nanographenes Built on a 1,4-Dihydropyrrolo[3,2-b]pyrrole Core

Here we present a highly versatile synthetic strategy based on twofold 6π-electrocyclization accompanied with HBr elimination as a novel approach towards centrosymmetric multi-heteroatom-doped nanographenes build around an electron-rich 1,4-dihydropyrrolo[3,2-b]pyrrole core. A straightforward synthesis from readily available substrates offers a unique possibility of fusing the 1,4-dihydropyrrolo[3,2-b]pyrrole subunit not only with carbocyclic building blocks, such as electron-deficient phenanthrenes, chrysenes, or [4]helicenes, but also with heterocyclic systems, such as benzo[b]furan and 5-thiatruxene. The clear advantage of this strategy is that there is no requirement to assemble complex scaffolds possessing bromoaryl units since bromine atom is introduced by bromination of 1,4-dihydropyrrolo[3,2-b]pyrrole core which, because of its exceptionally electron-rich character, is straightforward reaction. The obtained χ-shaped and S-shaped nanographenes containing 10 or more fused rings, exhibit visible-range emissions characterized by fluorescence quantum yields reaching 48 %. Computational studies of the reaction mechanism revealed that the 6π-electrocyclization is kinetically favourable over photo-induced direct arylation. Steady-state UV/Visible spectroscopy reveals that upon photoexcitation, the prepared S-shaped N-doped nanographenes undergo mostly radiative relaxation leading to large fluorescence quantum yields. We anticipate that this chemistry will empower the creation of new materials with various functionalities.

Rapid access to functionalized nanographenes through a palladium-catalyzed multi-annulation sequence

Nanographenes and polycyclic aromatic hydrocarbons exhibit many intriguing physical properties and have potential applications across a range of scientific fields, including electronics, catalysis, and biomedicine. To accelerate the development of such applications, efficient and reliable methods for accessing functionalized analogs are required. Herein, we report the efficient synthesis of functionalized small nanographenes from readily available iodobiaryl and diarylacetylene derivatives via a one-pot, multi-annulation sequence catalyzed by a single palladium catalyst. This method enables the preparation of small nanographenes bearing various polar functional groups, such as hydroxy, amino, and pyridinic nitrogen atoms, which are otherwise difficult to incorporate. These functional groups provide valuable sites for further derivatization, allowing the modulation of small nanographenes' solubility, optoelectronic properties, and photochromic and vapochromic behaviors. Our new method thus provides a platform for facile access to novel carbon-based materials.

Microwave-Assisted Palladium-Catalyzed Crossover-Annulation: Access to Fused Polycyclic Benzofuran Scaffolds

This study demonstrates quick access to heteroatom-embodied complex fused polycyclic frameworks through a palladium-catalyzed domino process facilitated by microwave-assisted crossover annulation of o-alkynylarylhalides and dihydrobenzofurans derivatives. The overall success of this process lies in the careful design of dihydrobenzofuran precursors that direct the initial palladium-mediated annulation step to proceed in a highly regioselective manner to furnish a single regioisomeric product. Notably, this one-pot method has witnessed good substrate scope and has furnished products with excellent yields.

Intermolecular Anionic Mixed-Valence and π-Dimer Complexes of ortho-Pentannulated Bisazacoronene Diimide

This study reports the serendipitous discovery of intermolecular anionic mixed-valence (MV) and π-dimer species in ortho-pentannulated BisAzaCoroneneDiimides (BACDs) during their electrochemical reduction in a non-aqueous solvent. A library of nitrogen-containing extended PDIs was synthesized via an aza-benzannulation reaction followed by a Pd-catalysed ortho-pentannulation reaction. Ortho-pentannulated BACDs revealed strong aggregation abilities in solution. Concentration-dependent UV/Vis absorption spectra, variable temperature 1H NMR experiments, and atomic force microscopy coupled to molecular dynamics support their self-assembly into columnar aggregates. Cyclic voltammetry experiments in dichloromethane reveal prominent splitting of the first reduction wave, attributed to the formation of unprecedented intermolecular anionic MV and π-dimers in organic solvent. These species were thoroughly characterized by real-time spectroelectrochemistry, electrochemical simulations and theoretical calculations. Remarkably, this work underscores the tuneable nature of AzaBenzannulatedPerylene Diimides (AzaBPDIs) and BACDs, emphasizing their potential as a promising scaffold for designing supramolecular materials with long-range radical anion delocalization. The observation of this phenomenon provides insights into the fundamental behaviour of supramolecular organic semiconductors, thereby paving the way for the development of novel electronic devices and electron-deficient materials.

Synthesis of acenaphthylene-fused heteroarenes and polyoxygenated benzo[j]fluoranthenes via a Pd-catalyzed Suzuki-Miyaura/C-H arylation cascade

Acenaphthylene-fused heteroarenes with a variety of five- and six-membered heterocycles such as thiophene, furan, benzofuran, pyrazole, pyridine and pyrimidine were synthesized via an efficient Pd-catalyzed reaction cascade in good to high yields (45-90%). This cascade involves an initial Suzuki-Miyaura cross-coupling reaction between 1,8-dihalonaphthalenes and heteroarylboronic acids or esters, followed by an intramolecular C-H arylation under the same conditions to yield the final heterocyclic fluoranthene analogues. The method was further employed to access polyoxygenated benzo[j]fluoranthenes, which are all structurally relevant to benzo[j]fluoranthene-based fungal natural products. The effectiveness of our strategy was demonstrated via a concise, four-step synthesis of the tetramethoxybenzo[j]fluoranthene derivative 18, which represents a formal total synthesis of the fungal natural product bulgarein.

Selective [3 + 2] C-H/C-H Alkyne Annulation via Dual (Distal) C(β, δ)-H Bond Activation Relay: A Novel Therapeutic Quinazolone-Tethered Benzofulvenes for Oral Cancer

In contrast to proximal C-H bond activations, distal C-H bond activation is fundamentally more challenging and requires distinctly specialized directing partners or techniques. In this context, we report an unprecedented dual (distal) β-C(benzylic)-H and δ-C(aryl)-H bond activation relay protocol for the chemo-, regio-, and stereoselective construction of heterocycle-tethered benzofulvenes via [3 + 2] CH/CH-alkyne annulation under palladium catalysis. The protocol overrides the more favorable [4 + 2] CH/NH annulation and does not follow the vinylic C-H bond activation pathway. Mechanistic studies provide insight into the favored cyclopalladation of key intermediates (resulting from β-C(benzylic)-H bond cleavage) through relay δ-C(aryl)-H cleavage (vs N-H cleavage) prior to reductive elimination, which is the key to desired annulation. The synthesized new chemical entities (NCEs) constitute a novel scaffold with favorable anticancer activity against oral squamous cell carcinoma (OSCC). Detailed biomolecular studies, including RNA-sequencing and analysis, indicate that these compounds (4e and 4w) arrest the cell cycle at the S-phase and target multiple cancer hallmarks, such as the activation of apoptotic pathways and impairment of mitochondrial activity simultaneously, suggesting their chemotherapeutic potential for oral cancer by addressing the complexity and adaptability of cancer cells in chorus.

Construction of acenaphthylenes via C-H activation-based tandem penta- and hexaannulation reactions

Acenaphthylene-containing polycyclic aromatic hydrocarbons (AN-PAHs) are noteworthy structural motifs for organic functional materials due to their non-alternant electronic structure, which increases electron affinity. However, the synthesis of AN-PAHs has traditionally required multiple sequential synthetic steps, limiting structural diversity. Herein, we present a tandem C-H penta- and hexaannulation reaction of aryl alkyl ketone with acetylenedicarboxylate. This integrated approach enhances overall efficiency and selectivity, marking a significant advancement in AN-PAH synthesis. Mechanistic studies unveil an orchestrated extension of five- and six-membered rings through C-H activation-annulation and Diels-Alder reaction. Additionally, the tandem annulation reaction can be performed stepwise, further validating the proposed mechanism and increasing the structural diversity of AN-PAHs.

Tether-entangled conjugated helices

A new design concept, tether-entangled conjugated helices (TECHs), is introduced for helical polyaromatic molecules. TECHs consist of a linear polyaromatic ladder backbone and periodically entangling tethers with the same planar chirality. By limiting the length of tether, all tethers synchronously bend and twist the backbone with the same manner, and change it into a helical ribbon with a determinate helical chirality. The 3D helical features are customizable via modular synthesis by using two types of synthons, the planar chiral tethering unit (C 2 symmetry) and the docking unit (C 2h symmetry), and no post chiral resolution is needed. Moreover, TECHs possess persistent chiral properties due to the covalent locking of helical configuration by tethers. Concave-type and convex-type oligomeric TECHs are prepared as a proof-of-concept. Unconventional double-helix π-dimers are observed in the single crystals of concave-type TECHs. Theoretical studies indicate the smaller binding energies in double-helix π-dimers than conventional planar π-dimers. A concentration-depend emission is found for concave-type TECHs, probably due to the formation of double-helix π-dimers in the excited state. All TECHs show strong circularly polarized luminescence (CPL) with dissymmetric factors (|g lum|) generally over 10-3. Among them, the (P)-T4-tBu shows the highest |g lum| of 1.0 × 10-2 and a high CPL brightness of 316 M-1 cm-1.

Post-Formation of Fused Pentagonal Structure on Fjord Region of Polyaromatic Hydrocarbons under Hydrothermal Conditions

This study explores the synthesis of cyclopenta-fused polyaromatic hydrocarbons (CP-PAHs) via Pt-catalyzed cyclization in water, focusing on the formation of fused pentagonal rings within heavily fused PAH frameworks. Utilizing platinum catalysts at lower temperatures (200-260 °C) in water, led to the successful synthesis of singly cyclized CP-PAHs. The reaction conditions facilitated the mono-cyclization of substrates such as dibenzo[g,p]chrysene and its isomers, yielding the desired products while suppressing the formation of bis-cyclized compounds. The use of Fe2O3 as an additive in conjunction with PtO2 was effective to suppress hydrogenation of the substrates and products. The products exhibited a redshift in UV-visible absorption and photoluminescence bands due to a decrease in the HOMO-LUMO energy gap. These findings highlight the potential of Pt-catalyzed cyclization for the controlled synthesis of CP-PAHs, with implications for various applications in materials science.

Palladium-Catalyzed Decarboxylative Annulation Reaction of Aryl Iodides and Methyl 2-Haloarenecarboxylates

A ligand-free palladium-catalyzed and norbornadiene-mediated annulation reaction of iodoarenes with methyl 2-haloarenecarboxylates is reported. The sequentially accomplished reaction comprises intermolecular C-H arylation, followed by intramolecular decarboxylative annulation, affording various valuable phenanthrenes. This reaction protocol could be expanded to triphenylene syntheses whereby norbornene was the cocatalyst. Interestingly, the decarboxylation of methyl esters was accomplished via solvent-mediated CMe-O bond cleavages.

Tethered Helical Ladder-Type Aromatic Lactams

Tethered nonplanar aromatics (TNAs) make up an important class of nonplanar aromatic compounds showing unique features. However, the knowledge on the synthesis, structures, and properties of TNAs remains insufficient. In this work, a new type of TNAs, the tethered aromatic lactams, is synthesized via Pd-catalyzed consecutive intramolecular direct arylations. These molecules possess a helical ladder-type conjugated system of up to 13 fused rings. The overall yields ranged from 3.4 to 4.3%. The largest of the tethered aromatic lactams, 6L-Bu-C14, demonstrates a guest-adaptive hosting capability of TNAs for the first time. When binding fullerene guests, the cavity of 6L-Bu-C14 became more circular to better accommodate spherical fullerene molecules. The host-guest interaction is thoroughly studied by X-ray crystallography, theoretical calculations, fluorescence titration, and nuclear magnetic resonance (NMR) titration experiments. 6L-Bu-C14 shows stronger binding with C70 than with C60 due to the better convex-concave π-π interaction. P and M enantiomers of all tethered aromatic lactams show distinct and persistent chiroptical properties and demonstrate the potential of chiral TNAs as circularly polarized luminescence (CPL) emitters.

Recent advances in the synthesis and applications of fluoranthenes

As an important subclass of polycyclic aromatic hydrocarbons (PAHs), fluoranthenes continue to attract significant attention in synthetic organic chemistry and materials science. In this article, an overview of recent advances in the synthesis of fluoranthene derivatives along with selected applications is provided. First, methods for fluoranthene synthesis with a classification based on strategic bond disconnections are discussed. Then, the total syntheses of natural products featuring the benzo[j]fluoranthene skeleton are covered. Finally, examples of important applications of a variety of fluoranthenes are summarized.

bay/ortho-Octa-substituted Perylene: A Versatile Building Block toward Novel Polycyclic (Hetero)Aromatic Hydrocarbons

ConspectusPolycyclic (hetero)aromatic hydrocarbons (PAHs) have emerged as a focal point in current interdisciplinary research, spanning the realms of chemistry, physics, and materials science. Possessing distinctive optical, electronic, and magnetic properties, these π-functional materials exhibit significant potential across diverse applications, including molecular electronic devices, organic spintronics, and biomedical functions, among others. Despite the extensive documentation of various PAHs over the decades, the efficient and precise synthesis of π-extended PAHs remains a formidable challenge, hindering their broader application. This challenge is primarily attributed to the intricate and often elusive nature of their synthesis, compounded by issues related to low solubility and unfavored stability.The development of π-building blocks that can be facilely and modularly transformed into diverse π-frameworks constitutes a potent strategy for the creation of novel PAH materials. For instance, based on the classic perylene diimide (PDI) unit, researchers such as Würthner, Wang, and Nuckolls have successfully synthesized a plethora of structurally diverse PAHs, as well as numerous other π-functional materials. However, until now the availability of such versatile building blocks is still severely limited, especially for those simultaneously having a facile preparation process, adequate solubilizing groups, favored material stability, and critically, rich possibilities for structural extension spaces.In this Account, we present an overview of our invention of a highly versatile bay-/ortho-octa-substituted perylene building block, designated as Per-4Br, for the construction of a series of novel PAH scaffolds with tailor-made structures and rich optoelectronic and magnetic properties. First, starting with a brief discussion of current challenges associated with the bottom-up synthesis of π-extended PAHs, we rationalize the key features of Per-4Br that enable facile access to new PAH molecules including its ease of large-scale preparation, favored material stability and solubility, and multiple flexible reaction sites, with a comparison to the PDI motif. Then, we showcase our rational design and sophisticated synthesis of a body of neutral or charged, closed- or open-shell, curved, or planar PAHs via controlled annulative π-extensions in different directions such as peripheral, diagonal, or multiple dimensions of the Per-4Br skeleton. In this part, the fundamental structure-property relationships between molecular conformations, electronic structures, and self-assembly behaviors of these PAHs and their unique physiochemical properties such as unusual open-shell ground states, global aromaticity, state-associated/stimuli-responsive magnetic activity, and charge transport characteristics will be emphatically elaborated. Finally, we offer our perspective on the continued advancement of π-functional materials based on Per-4Br, which, we posit, may stimulate heightened research interest in the versatile structural motifs typified by Per-4Br, consequently catalyzing further progress in the realm of organic π-functional materials.

Mono or double Pd-catalyzed C-H bond functionalization for the annulative π-extension of 1,8-dibromonaphthalene: a one pot access to fluoranthene derivatives

The Pd-catalyzed annulative π-extension of 1,8-dibromonaphthalene for the preparation of fluoranthenes in a single operation has been investigated. With specific arenes such as fluorobenzenes, the Pd-catalyzed double functionalization of C-H bonds yields the desired fluoranthenes. The reaction proceeds via a palladium-catalyzed direct intermolecular arylation, followed by a direct intramolecular arylation step. As the C-H bond activation of several benzene derivatives remains very challenging, the preparation of fluoranthenes from 1,8-dibromonaphthalene via Suzuki coupling followed by intramolecular C-H activation has also been investigated to provide a complementary method. Using the most appropriate synthetic route and substrates, it is possible to introduce the desired functional groups at positions 7-10 on fluoranthenes.

Luminescent Chiral Furanol-PAHs via Straightforward Ni-Catalysed Csp2 -F Functionalization: Mechanistic Insights into the Scholl Reaction

Here we report the stepwise synthesis of new nanographenes (NGs) and polycyclic aromatic hydrocarbons (PAHs) obtained via Scholl ring fusion applied at aromatic homologation compounds, which are obtained through one-step Ni-catalysed Csp2 -F functionalization. The latter are rapidly accessed valid precursors for the Scholl reaction, and screening of experimental conditions allowed us to describe for the first time furanol-bearing PAHs. Mechanistic insights are obtained by DFT to rationalize the formation of the furanol PAHs under moderately acidic conditions. All PAHs and NGs synthesized show moderate/weak fluorescent properties, and all PAHs crystallized show some degree of curvature and are obtained as racemic mixtures. Enantiomeric separation by chiral HPLC of one furanol-bearing PAH allowed the study of their chiroptical CD properties.

Bespoke Tailoring of Graphenoid Sheets: A Rippled Molecular Carbon Comprising Cyclically Fused Nonbenzenoid Rings

The incorporation of nonbenzenoid rings into the hexagonal networks of graphenoid nanostructures is of immense importance for electronic, magnetic, and mechanical properties, but the underlying mechanisms of nonbenzenoid ring fusion are rather unexplored. Here, we report the synthesis and characterization of a rippled C84 molecular carbon, which contains 10 nonbenzenoid rings (five-, seven-, and eight-membered rings) that are contiguously fused to give a cyclic geometry. The fused nonbenzenoid rings impart high solubility, configurational stability, multiple reversible redox behaviors, unique aromaticity, and a narrow band gap to the system. Moreover, this carbon nanostructure allows for further functionalization via electrophilic substitution and metalation reactions, enabling access to finely tuned derivatives. Interestingly, both the bowl-shaped and planar conformations of the core in molecular carbon are observed in the solid state. Additionally, this molecular carbon displays ambipolar transport characteristics.

Tunable Regioselectivity in C-H-Activated Direct Arylation Reactions of Dithieno[3,2-b:2',3'-d]pyrroles

In this study, regioselectively controlled direct arylation of dithieno[3,2-b:2,3'-d]pyrroles (DTPs) is reported. By carefully selecting the catalytic system, Pd source, ligand, and additives, we achieved either selective N-arylation or unprecedented β-arylation and β,β'-diarylation of the DTP core through C-H activation when reacting unsubstituted H-DTP with 9-anthracenyl halides. For N-substituted DTPs, we obtained regioselective carboxylate-assisted arylation of the α-position(s). Consequently, depending on the catalytic system and substitution at the DTP nitrogen, we successfully synthesized novel regioselectively substituted DTPs, including N-aryl, rarely reported β-aryl, β,β'-diaryl, α-aryl, and α,α'-diaryl scaffolds. These compounds can be straightforwardly prepared and further functionalized for applications as organic electronic materials.

Utilization of Aryl(TMP)iodonium Salts for Copper-Catalyzed N-Arylation of Isatoic Anhydrides: An Avenue to Fenamic Acid Derivatives and N,N'-Diarylindazol-3-ones

Herein, we report a general method for copper-catalyzed N-arylation of isatoic anhydrides with unsymmetrical iodonium salts at room temperature. The developed catalytic protocol is mild and operationally simple, and aryl(TMP)iodonium trifluoroacetate is employed as the arylating partner. The methodology offers the broad applicability of both structurally and electronically diverse aryl groups from aryl(TMP)iodonium salts to access N-arylated isatoic anhydrides in moderate to excellent yields (53-92%). Moreover, the substituted isatoic anhydrides are equally compatible with the protocol too. To demonstrate the synthetic utilities of the N-arylation process, we also report an alternative approach for biologically relevant fenamic acid derivatives and N,N'-diarylindazol-3-ones in a one-pot step economical system. In addition, the scale-up synthesis of flufenamic acid is also illustrated.

Saddle-shaped aza-nanographene with multiple odd-membered rings

A saddle-shaped aza-nanographene containing a central 1,4-dihydropyrrolo[3,2-b]pyrrole (DHPP) has been prepared via a rationally designed four-step synthetic pathway encompassing intramolecular direct arylation, the Scholl reaction, and finally photo-induced radical cyclization. The target non-alternant, nitrogen-embedded polycyclic aromatic hydrocarbon (PAH) incorporates two abutting pentagons between four adjacent heptagons forming unique 7-7-5-5-7-7 topology. Such a combination of odd-membered-ring defects entails a negative Gaussian curvature within its surface with a significant distortion from planarity (saddle height ≈ 4.3 Å). Its absorption and fluorescence maxima are located in the orange-red region, with weak emission originating from the intramolecular charge-transfer character of a low-energy absorption band. Cyclic voltammetry measurements revealed that this stable under ambient conditions aza-nanographene underwent three fully reversible oxidation steps (two one-electron followed by one two-electron) with an exceptionally low first oxidation potential of E ox1 = -0.38 V (vs. Fc/Fc+).

Electronic Control of the Scholl Reaction: Selective Synthesis of Spiro vs Helical Nanographenes

Scholl oxidation has become an essential reaction in the bottom-up synthesis of molecular nanographenes. Herein, we describe a Scholl reaction controlled by the electronic effects on the starting substrate (1 a, b). Anthracene-based polyphenylenes lead to spironanographenes under Scholl conditions. In contrast, an electron-deficient anthracene substrate affords a helically arranged molecular nanographene formed by two orthogonal dibenzo[fg,ij]phenanthro-[9,10,1,2,3-pqrst]pentaphene (DBPP) moieties linked through an octafluoroanthracene core. Density Functional Theory (DFT) calculations predict that electronic effects control either the first formation of spirocycles and subsequent Scholl reaction to form spironanographene 2, or the expected dehydrogenation reaction leading solely to the helical nanographene 3. The crystal structures of four of the new spiro compounds (syn 2, syn 9, anti 9 and syn 10) were solved by single crystal X-ray diffraction. The photophysical properties of the new molecular nanographene 3 reveal a remarkable dual fluorescent emission.

Molecular Engineering of Chalcogen-Embedded Anthanthrenes via peri-Selective C-H Activation: Fine-Tuning of Crystal Packing for Organic Field-Effect Transistors

Disclosed herein is a RhCl₃ -catalyzed peri-selective C-H/C-H oxidative homo-coupling of 1-substituted naphthalenes, which provides a highly efficient and streamlined approach to chalcogen-embedded anthanthrenes from readily available starting materials. Introducing O, S, and Se into the anthanthrene skeleton leads to gradually increased π-π stacking distances but significantly enhanced π-π overlaps with the growth of the hetero-atom radius. Moderate π-π distance, overlap area, and intermolecular S-S interactions endow S-embedded anthanthrene (PTT) with excellent 2D charge-transport properties. Moreover, the transformation of p-type to n-type S-embedded anthanthrenes is realized for the first time via the S-atom oxidation from PTT to PTT-O4. In organic field-effect transistor devices, PTT derivatives exhibit hole transport with mobilities up to 1.1 cm²  V^-1  s^-1 , while PTT-O4 shows electron transport with a mobility of 0.022 cm²  V^-1  s^-1 .

Transition-metal-catalyzed ortho C-H functionalization of 2-arylquinoxalines

Recently, direct C-H bond activation and functionalization has become a prodigious and hot topic among synthetic organic chemists due to its step-economic nature and substantial synthetic versatility. On the other hand, quinoxaline, a fused bicycle of benzene and pyrazine, has omnipresent applications in medicinal-, industrial- and materials chemistry. The presence of the N-1 atom in 2-arylquinoxaline enables chelation formation with a metal catalyst leading to the formation of ortho-substituted products. In this review, all articles related to the ortho C-H bond functionalization of 2-arylquinoxalines published up to May 2022 are highlighted.

Green-Emitting 4,5-Diaminonaphthalimides in Activity-Based Probes for the Detection of Thrombin

The natures of electron-donating groups as well as the bridge between them determine the fate of substituted 1,8-naphthalimide molecules in the excited state. An activity-based probe constructed from a selective peptide sequence, a reactive warhead, and the brightest green-emitting fluorophore displays impressive performance for thrombin protease detection in a newly constructed series of 1,8-naphthalimides.

Rapid access to polycyclic N-heteroarenes from unactivated, simple azines via a base-promoted Minisci-type annulation

Conventional synthetic methods to yield polycyclic heteroarenes have largely relied on metal-mediated arylation reactions requiring pre-functionalised substrates. However, the functionalisation of unactivated azines has been restricted because of their intrinsic low reactivity. Herein, we report a transition-metal-free, radical relay π-extension approach to produce N-doped polycyclic aromatic compounds directly from simple azines and cyclic iodonium salts. Mechanistic and electron paramagnetic resonance studies provide evidence for the in situ generation of organic electron donors, while chemical trapping and electrochemical experiments implicate an iodanyl radical intermediate serving as a formal biaryl radical equivalent. This intermediate, formed by one-electron reduction of the cyclic iodonium salt, acts as the key intermediate driving the Minisci-type arylation reaction. The synthetic utility of this radical-based annulative π-extension method is highlighted by the preparation of an N-doped heptacyclic nanographene fragment through fourfold C–H arylation.

The functionalisation of unactivated azines has been restricted because of their intrinsic low reactivity. Here the authors show a transition-metal-free, radical relay π-extension approach to produce N-doped polycyclic aromatic compounds directly from simple azines and cyclic iodonium salts.

Remote Construction of N-Heterocycles via 1,4-Palladium Shift-Mediated Double C-H Activation

In the past years, Pd0 -catalyzed C(sp3 )-H activation provided efficient and step-economical methods to synthesize carbo- and heterocycles via direct C(sp2 )-C(sp3 ) bond formation. We report herein that a 1,4-Pd shift allows access to N-heterocycles which are difficult to build via a direct reaction. It is shown that o-bromo-N-methylanilines undergo a 1,4-Pd shift at the N-methyl group, followed by intramolecular trapping by C(sp2 )-H or C(sp3 )-H activation at another nitrogen substituent and remote C-C bond formation to generate biologically relevant isoindolines and β-lactams. The product selectivity is influenced by the employed ligand, with NHCs favoring the product of remote C-C coupling against products arising from direct C-C coupling and N-demethylation.

Construction of Substituted [4]Acene Frameworks Based on Double Cationic Cyclizations of Fluoroalkenes

In this study, 5-substituted and 5,6-disubstituted [4]acenes were synthesized by the double cationic cyclization of fluoroalkenes. (a) After being treated with Me2AlCl (1.2 equiv), 2-trifluoromethyl-1-alkenes bearing two aryl groups underwent domino Friedel–Crafts-type cyclization (two-ring construction) followed by dehydrogenation to generate 5-fluorinated [4]acenes. The same (trifluoromethyl)alkenes were treated with both Me2AlCl (1.2 equiv) and Me3Al (1.0 equiv), resulting in selective one-ring construction and the creation of bicyclic 1,1-difluoro-1-alkenes. (b) When treated with triflic acid, the bicyclic difluoroalkenes underwent regioselective protonation to generate CF2 cations; Friedel–Crafts-type cyclization of these cations provided tetracyclic ketones. The obtained ketones act as an appropriate platform for the introduction of substituents at the 5-position of [4]acenes. (c) When treated with DDQ/H+, the bicyclic difluoroalkenes underwent oxidative generation of allylic CF2 cations; Friedel–Crafts-type cyclization of these cations produced tetracyclic enones. The enones were subjected to double addition of carbanions to facilitate the introduction of two substituents at the 5- and 6-positions of dihydro[4]acenes.

Preparative Production of Functionalized (N- and O-Heterocyclic) Polycyclic Aromatic Hydrocarbons by Human Cytochrome P450 3A4 in a Bioreactor

Polycyclic aromatic hydrocarbons (PAHs) and their N- and O-containing derivatives (N-/O-PAHs) are environmental pollutants and synthetically attractive building blocks in pharmaceuticals. Functionalization of PAHs can be achieved via C-H activation by cytochrome P450 enzymes (e.g., P450 CYP3A4) in an environmentally friendly manner. Despite its broad substrate scope, the contribution of CYP3A4 to metabolize common PAHs in humans was found to be small. We recently showcased the potential of CYP3A4 in whole-cell biocatalysis with recombinant yeast Komagataella phaffii (Pichia pastoris) catalysts for the preparative-scale synthesis of naturally occurring metabolites in humans. In this study, we aimed at exploring the substrate scope of CYP3A4 towards (N-/O)-PAHs and conducted a bioconversion experiment at 10 L scale to validate the synthetic potential of CYP3A4 for the preparative-scale production of functionalized PAH metabolites. Hydroxylated products were purified and characterized using HPLC and NMR analysis. In total, 237 mg of fluorenol and 48 mg of fluorenone were produced from 498 mg of fluorene, with peak productivities of 27.7 μmol/L/h for fluorenol and 5.9 μmol/L/h for fluorenone; the latter confirmed that CYP3A4 is an excellent whole-cell biocatalyst for producing authentic human metabolites.

Domino Dehydrative π-Extension: A Facile Path to Extended Perylenes and Terrylenes

Herein, we report a new method for synthesis of extended perylenes and terrylenes. The technique is based on the cascade dehydrative π-extensions (DPEX) of aryl aldehydes, in which stepwise annulations activate previously "dormant" substituents. Two- and fourfold cyclizations of 3-aryl-biphenyl-2,2'-dicarbaldehydes offer a rapid path to unsymmetrical perylenes and elusive terrylene derivatives, respectively. DPEX of 3,3''-(phenanthrene-1,8-diyl)bis (([1,1'-biphenyl]-2,2'-dicarbaldehyde)) leads to the biradical structure, which proceeds in situ into oxidative electrocyclization at room temperature. The described domino process complements and expands DPEX approach to a large family of fused acenes and related PAHs.

Late-Stage Functionalisation of Polycyclic (N-Hetero-) Aromatic Hydrocarbons by Detoxifying CYP5035S7 Monooxygenase of the White-Rot Fungus Polyporus arcularius

Functionalisation of polycyclic aromatic hydrocarbons (PAHs) and their N-heteroarene analogues (NPAHs) is a tedious synthetic endeavour that requires diverse bottom-up approaches. Cytochrome P450 enzymes of white-rot fungi were shown to participate in the fungal detoxification of xenobiotics and environmental hazards via hydroxylation of PAH compounds. In this paper, the recently discovered activity of the monooxygenase CYP5035S7 towards (N)PAHs was investigated in detail, and products formed from the substrates azulene, acenaphthene, fluorene, anthracene, and phenanthrene by whole-cell biocatalysis were isolated and characterised. The observed regioselectivity of CYP5035S7 could be explained by a combination of the substrate's electron density and steric factors influencing the substrate orientation giving insight into the active-site geometry of the enzyme.

Ortho C-H Functionalization of 2-Arylimidazo[1,2-a]pyridines

C-H activation and functionalization is quite promising in recent days as the strategy offers a go-to general method for different bond formations and hence grants synthetic versatility. At the same time, imidazopyridine, a fused bicycle of imidazole moiety with pyridine ring, has a profound impact due to its ubiquitous and prodigious application in medicinal as well as material chemistry. The presence of N-1 atom in 2-arylImidazo[1,2-a]pyridine facilitates the coordination with metal catalysts leading to the formation of ortho-substituted products. This review summarizes all the articles on ortho C-H functionalization of 2-arylImidazo[1,2-a]pyridines published till August 2021.

Cyclometallated complexes as catalysts for C-H activation and functionalization

The development of novel catalysts for C-H activation reactions with increased reactivity and improved selectivities has been attracting significant interest over the last two decades. More recently, promising results have been developed using tridentate pincer ligands, which form a stable C-M bond. Furthermore, based on mechanistic studies, the unique catalytic role of some metallacyclic intermediate species has been revealed. These experimental observations have subsequently translated into the rational design of advanced C-H activation catalysts in both Ru- and Ir-based systems. Recent breakthroughs in the field of C-H activation catalysed by metallacyclic intermediates are thus discussed.

Construction of Heptagon-Containing Molecular Nanocarbons

Molecular nanocarbons containing heptagonal rings have attracted increasing interest due to their dynamic behavior, electronic properties, aromaticity, and solid-state packing. Heptagon incorporation can not only induce negative curvature within nanocarbon scaffolds, but also confer significantly altered properties through interaction with adjacent non-hexagonal rings. Despite the disclosure of several beautiful examples in recent years, synthetic strategies toward heptagon-embedded molecular nanocarbons remain relatively limited due to the intrinsic challenges of heptagon formation and incorporation into polyarene frameworks. In this Review, recent advances in solution-mediated and surface-assisted synthesis of heptagon-containing molecular nanocarbons, as well as the intriguing properties of these frameworks, will be discussed.

Recent advances in rhodium-catalyzed C(sp2)-H (hetero)arylation

Arylation is a common behaviour in organic synthesis for the construction of complex structures, especially the biaryls. Among those reported arylation procedures, transition-metal-catalyzed direct C(sp²)-H arylation has been rapidly developed in recent decades and has become a reliable alternative to traditional cross-coupling procedures using organometallic reagents. Great achievements in rhodium-catalyzed C(sp²)-H arylation have been witnessed during the last decade. Aryl halides, simple arenes, aryl boronic acids, arylsilanes, aryl aldehyde, aryl carboxylic acid, diazides, etc. were successfully utilized as arylating reagents under rhodium-catalyzed conditions. In this review, recent achievements in rhodium-catalyzed arylations through C(sp²)-H bond activation were summarized together with the mechanism discussions.

Broadening of horizons in the synthesis of CD3-labeled molecules

In the light of the recent potentials of deuterated molecules as pharmaceuticals or even in mechanistic understanding, efficient methods for their synthesis are continually desired. CD₃-containing molecules are prominent amongst these motifs due to the parallel of the "magic methyl effect": introducing a methyl group into pharmaceuticals could positively affect biological activities. The trideuteromethyl group is bound to molecules either by C, N, O, or S atom. For a long time, the preparation methods of such labeled compounds were underestimated and involved multi-step syntheses. More recently, specific approaches dealing with the direct incorporation of the CD₃ group have been developed. This Review gives an overview of the methods for the preparation of CD₃-labeled molecules from conventional functional group interconversion techniques to catalytic approaches and include radical strategy. Detailed reaction mechanisms are also discussed.