One-Pot Synthesis of Dihydrobenzo[a]fluorenes via Cascade C-H Annulation of Thiobenzamide with Alkynes.

We herein disclose a highly efficient one-pot synthetic strategy for dihydrobenzo[a]fluorenes via cascade rhodium(III)-catalyzed ortho-C-H activation/annulation of thiobenzamides with aryl ethynyl ketones and subsequently copper(II)-promoted intramolecular C-H/C-H cross-coupling reactions. Mechanistic investigations suggest that Cu(II) plays two crucial roles by serving as a sulfide scavenger to regenerate the Rh(III) catalyst and promoting the intramolecular C-H/C-H cross-coupling reaction. This protocol greatly streamlines accesses to a variety of appealing tetracyclic benzo[a]fluorene skeletons, which may have potential biological activity and medicinal properties.

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 .

Iridium(III)-Catalyzed Diarylation/Annulation of Benzoic Acids: Facile Access to Multi-Aryl Spirobifluorenes as Pure Hydrocarbon Hosts for High-Performance OLEDs.

Herein disclosed is the first example of diarylation/annulation of benzoic acids via an iridium catalyst system. This protocol provides a step-economic and highly efficient pathway to 1-aryl, 1,3-diaryl, 1,7-diaryl and 1,3,7-triaryl spirobifluorenes from readily available starting materials. The applications of multi-aryl spirobifluorenes as pure hydrocarbon (PHC) hosts for red, green, and blue (RGB) phosphorescent organic light-emitting diodes (PhOLEDs) were explored. Due to high triplet energies, 1,3-diaryl spirobifluorenes exhibit the potential as the host material of blue PhOLEDs. 1,7-Diaryl spirobifluorene can serve as the host of green PhOLEDs. 1,3,7-Triaryl spirobifluorene is a high-performance host for red PhOLEDs, which exhibits a high external quantum efficiency (EQE) up to 27.3 %. This work not only exemplifies the great potential of multi-aryl spirobifluorenes as PHC hosts, but also offers a new approach for the synthesis of these PHC hosts.

Dearomatizing [4+1] Spiroannulation of Naphthols: Discovery of Thermally Activated Delayed Fluorescent Materials.

Disclosed here is a palladium-catalyzed direct [4+1] spiroannulation of ortho-C-H bonds of naphthols with cyclic diaryliodonium salts to construct spirofluorenyl naphthalenones (SFNP) under mild reaction conditions. This spiroannulation directly transforms the hydroxy group into a carbonyl group, and also tolerates reactive functional groups such as the halo groups, which provide an opportunity to rapidly assemble structurally new thermally activated delayed fluorescent (TADF) materials that feature a carbonyl group with an adjacent spirofluorenyl unit as the acceptor. As an illustrated example, the OLED device utilizing the assembled DMAC-SFNP as the host material exhibits a low turn-on voltage of 2.5 V and an ultra-high external quantum efficiency of 32.2 %. This work provides inspiration for structurally new TADF materials, and also displays the potential of C-H activation as a synthetic strategy for the innovation of optoelectronic materials.

Molecular Design of Non-doped OLEDs Based on a Twisted Heptagonal Acceptor: A Delicate Balance between Rigidity and Rotatability.

The development of efficient non-doped organic light-emitting diodes (OLEDs) is highly desired but very challenging because of a severe aggregation-caused quenching effect. Herein, we present a heptagonal diimide acceptor (BPI), which can restrict excessive intramolecular rotation and inhibit close intermolecular π-π stacking due to well-balanced rigidity and rotatability of heptagonal structure. The BPI-based luminogen (DMAC-BPI) shows significant aggregation-induced delayed florescence with an extremely high photoluminescence quantum yield (95.8 %) of the neat film, and the corresponding non-doped OLEDs exhibit outstanding electroluminescence performance with maximum external quantum efficiency as high as 24.7 % and remarkably low efficiency roll-off as low as 1.0 % at 1000 cd m-2 , which represents the state-of-the-art performance for non-doped OLEDs. In addition, the synthetic route to DMAC-BPI is greatly streamlined and simplified through oxidative Ar-H/Ar-H homo-coupling reaction.

Construction of Cationic Azahelicenes: Regioselective Three-Component Annulation Using In Situ Activation Strategy.

Described herein is a strategy to construct cationic azahelicenes through the three-component annulation reaction of isoquinoline, indole, and 1,2-dichloroethane (DCE), in which DCE serves as an in situ activating agent for C1-H activation of isoquinoline, a vinyl equivalent, and a solvent. This in situ activation annulation reaction features a facile one-step synthesis and complete regioselectivity. The complete regioselectivity of C1 over C3 for the isoquinoline ring paves a path to the helical structure in a highly ordered sequence. One of the synthesized ionic [5]azahelicenium fluorophores exhibits the potential to serve as a mitochondria-targeted biomarker with good photostability and low cytotoxicity.

Copper-catalyzed remote C-H arylation of polycyclic aromatic hydrocarbons (PAHs).

The regioselective C-H arylation of substituted polycyclic aromatic hydrocarbons (PAHs) is a desired but challenging task. A copper-catalyzed C7-H arylation of 1-naphthamides has been developed by using aryliodonium salts as arylating reagents. This protocol does not need to use precious metal catalysts and tolerates wide variety of functional groups. Under standard conditions, the remote C-H arylation of other PAHs including phenanthrene-9-carboxamide, pyrene-1-carboxamide and fluoranthene-3-carboxamide has also accomplished, which provides an opportunity for the development of diverse organic optoelectronic materials.

Double ortho-C-H Activation/Annulation of Benzamides with Aryl Alkynes: A Route to Double-Helical Polycyclic Heteroaromatics.

It remains a challenge to achieve N,O-double annulations of primary benzamides with aryl alkynes due to competitive N,N-double annulations. Herein, we employed sterically hindered 1-methylcyclohexane-1-carboxylic acid to address this challenge, the double ortho-C-H activation of benzamides and subsequent N,O-double annulations with aryl alkynes have been accomplished for the first time. The resulting product can be further transformed into a double-helical extended π-conjugated polycyclic heteroarene via Scholl oxidation, which exhibits blue emission with high fluorescence quantum yields.

Oxidative C-H/C-H Coupling Reactions between Two (Hetero)arenes.

Transition metal-mediated C-H bond activation and functionalization represent one of the most straightforward and powerful tools in modern organic synthetic chemistry. Bi(hetero)aryls are privileged π-conjugated structural cores in biologically active molecules, organic functional materials, ligands, and organic synthetic intermediates. The oxidative C-H/C-H coupling reactions between two (hetero)arenes through 2-fold C-H activation offer a valuable opportunity for rapid assembly of diverse bi(hetero)aryls and further exploitation of their applications in pharmaceutical and material sciences. This review provides a comprehensive overview of the fundamentals and applications of transition metal-mediated/catalyzed oxidative C-H/C-H coupling reactions between two (hetero)arenes. The substrate scope, limitation, reaction mechanism, regioselectivity, and chemoselectivity, as well as related control strategies of these reactions are discussed. Additionally, the applications of these established methods in the synthesis of natural products and exploitation of new organic functional materials are exemplified. In the last section, a short introduction on oxidant- or Lewis acid-mediated oxidative Ar-H/Ar-H coupling reactions is presented, considering that it is a very powerful method for the construction of biaryl units and polycylic arenes.

DOTA Functionalized Cross-Linked Small-Molecule Micelles for Theranostics Combining Magnetic Resonance Imaging and Chemotherapy.

Herein, a new theranostic nanoplatform was built by introducing DOTA on the surface of the cross-linked small molecular micelles. This nanoplatform consisted of three parts: (1) Hydrophobic alkyl chain functioned with alkenes as cross-linkable part to ensure the robust stability in vivo; (2) Hydrophilic DOTA for not only gadolinium ions complexion as MR imaging contrast agents but also platinum ions complexion as drug carriers; (3) Cisplatin as antitumor drug and MR imaging amplifier simultaneously. The metal loading content of the resulting Pt/Gd@DOTA-CSMs was up to 12 and 14 wt % for Gd(III) and Pt(II), respectively. The longitudinal relaxation rate of Gd@DOTA-CSMs (8.46 mM-1 s-1) was 2.6 times than that of the clinical Gd-DTPA (3.23 mM-1 s-1). When cisplatin was involved, not only great antitumor efficiency was achieved, but higher longitudinal relaxation rate of Pt/Gd@DOTA-CSMs (11.17 mM-1 s-1) was carried out due to the extension of rotational correlation time. The experiments of Balb/c mice bearing 4T1 xenograft indicated that Pt/Gd@DOTA-CSMs had better antitumor activity, lower side effect than clinically used cisplatin, and greater MR imaging than Gd-DTPA. All the results proved that the nanoplatform of DOTA-CSMs held remarkable potential in the field of therapeutics.

Construction of 3,7-Dithienyl Phenothiazine-Based Organic Dyes via Multistep Direct C-H Arylation Reactions.

Herein, an effective and feasible approach to prepare 3,7-dithienyl phenothiazine-based organic dyes has been developed. In this synthetic procedure, the Pd-catalyzed multistep direct C-H arylation of thiophene derivatives with phenothiazine bromides was employed for the first time to construct the 3,7-dithienyl phenothiazine core scaffold, which greatly streamlines access to this class of organic dyes. 3-Thienyl phenothiazine-based dyes were also synthesized via the direct C-H arylation of thiophenes as references. Most of the 3,7-dithienyl phenothiazine-based dyes exhibit better photovoltaic performances than the 3-thienyl phenothiazine-based dyes. Among these organic dyes, the solar cell device based on 6d exhibits the highest conversion efficiency of 8.9%. Compared with 6d, organic dyes with longer π-conjugation, also including bithiophene as the π-spacer, show dramatically reduced conversion efficiencies of cell devices. The introduction of the more electron-rich 3,4-ethylenedioxythiophene to the C3- and/or C7-position of phenothiazine instead of thiophene does not significantly improve the photoelectric conversion performance. The highly efficient synthetic strategy herein developed and these primary results may be helpful to design and synthesize a variety of new 3,7-dithienyl phenothiazine-based organic dyes.

Pd-Catalyzed Direct C-H Functionalization/Annulation of BODIPYs with Alkynes to Access Unsymmetrical Benzo[ b]-Fused BODIPYs: Discovery of Lysosome-Targeted Turn-On Fluorescent Probes.

A highly efficient palladium-catalyzed direct C-H functionalization/annulation of BODIPYs with alkynes has been developed for the first time to construct a series of unsymmetrical benzo[ b]-fused BODIPYs from readily available starting materials. These unsymmetrical benzo[ b]-fused BODIPYs exhibit remarkably red-shifted emissions and larger Stokes shifts than classical BODIPY dyes. Cell imaging experiments and cytotoxicity assays demonstrate that BODIPYs 4c and 4d have specific lysosome-labeling capacities, turn-on fluorescence emissions in cells, and low cytotoxicity.

Iridium-Catalyzed Annulation Reactions of Thiophenes with Carboxylic Acids: Direct Evidence for a Heck-type Pathway.

The functionalization of thiophenes is a fundamental and important reaction. Herein, we disclose iridium-catalyzed one-pot annulation reactions of (benzo)thiophenes with (hetero)aromatic or α,ß-unsaturated carboxylic acids, which afford thiophene-fused coumarin-type frameworks. Dearomatization reactions of 2-substituted thiophenes with α,ß-unsaturated carboxylic acids deliver various thiophene-containing spirocyclic products. The occurrence of two interconnected reactions provides direct evidence for a Heck-type pathway. The mechanistic scenario described herein is distinctly different from the SE Ar and concerted metalation-protodemetalation (CMD) pathways encountered in the well-described oxidative C-H/C-H cross-coupling reactions of thiophenes with other heteroarenes.

Oxidative C-H/C-H Cross-Coupling Reactions between N-Acylanilines and Benzamides Enabled by a Cp*-Free RhCl3 /TFA Catalytic System.

By making use of a dual-chelation-assisted strategy, a completely regiocontrolled oxidative C-H/C-H cross-coupling reaction between an N-acylaniline and a benzamide has been accomplished for the first time. This process constitutes a step-economic and highly efficient pathway to 2-amino-2'-carboxybiaryl scaffolds from readily available substrates. A Cp*-free RhCl3 /TFA catalytic system was developed to replace the [Cp*RhCl2 ]2 /AgSbF6 system generally used in oxidative C-H/C-H cross-coupling reactions between two (hetero)arenes (Cp*=pentamethylcyclopentadienyl, TFA=trifluoroacetic acid). The RhCl3 /TFA system avoids the use of the expensive Cp* ligand and AgSbF6 . As an illustrative example, the procedure developed herein greatly streamlines the total synthesis of the naturally occurring benzo[c]phenanthridine alkaloid oxynitidine, which was accomplished in excellent overall yield.

Unparalleled Ease of Access to a Library of Biheteroaryl Fluorophores via Oxidative Cross-Coupling Reactions: Discovery of Photostable NIR Probe for Mitochondria.

The development of straightforward accesses to organic functional materials through C-H activation is a revolutionary trend in organic synthesis. In this article, we propose a concise strategy to construct a large library of donor-acceptor-type biheteroaryl fluorophores via the palladium-catalyzed oxidative C-H/C-H cross-coupling of electron-deficient 2H-indazoles with electron-rich heteroarenes. The directly coupled biheteroaryl fluorophores, named Indazo-Fluors, exhibit continuously tunable full-color emissions with quantum yields up to 93% and large Stokes shifts up to 8705 cm(-1) in CH2Cl2. By further fine-tuning of the substituent on the core skeleton, Indazo-Fluor 3l (FW = 274; λem = 725 nm) is obtained as the lowest molecular weight near-infrared (NIR) fluorophore with emission wavelength over 720 nm in the solid state. The NIR dye 5h specifically lights up mitochondria in living cells with bright red luminescence. Typically, commercially available mitochondria trackers suffer from poor photostability. Indazo-Fluor 5h exhibits superior photostability and very low cytotoxicity, which would be a prominent reagent for in vivo mitochondria imaging.

Molecular Engineering of Mechanochromic Materials by Programmed C-H Arylation: Making a Counterpoint in the Chromism Trend.

The development of facile methods for screening organic functional molecules through C-H bond activation is a revolutionary trend in materials research. The prediction of mechanochromism as well as mechanochromic trends of luminogens is an appealing yet challenging puzzle. Here, we present a strategy for the design of mechanochromic luminogens based on the dipole moment of donor-acceptor molecules. For this purpose, a highly efficient route to 2,7-diaryl-[1,2,4]triazolo[1,5-a]pyrimidines (2,7-diaryl-TAPs) has been established through programmed C-H arylation, which unlocks a great opportunity to rapidly assemble a library of fluorophores for the discovery of mechanochromic regularity. Molecular dipole moment can be employed to explain and further predict the mechanochromic trends. The 2,7-diaryl-TAPs with electron-donating groups on the 2-aryl and electron-withdrawing groups on the 7-aryl possess a relatively small dipole moment and exhibit a red-shifted mechanochromism. When the two aryls are interchanged, the resulting luminogens have a relatively large dipole moment and display a blue-shifted mechanochromism. Seven pairs of isomers with opposite mechanochromic trends are presented as illustrative examples. The aryl-interchanged congeners with a bidirectional emission shift are structurally similar, which provides an avenue for understanding in-depth the mechanochromic mechanism.

Gold-catalyzed cascade C-H/C-H cross-coupling/cyclization/alkynylation: an efficient access to 3-alkynylpyrroles.

An efficient approach to 3-alkynylpyrroles has been developed through the gold-catalyzed reaction of ß-enamino derivatives with terminal alkynes, which features complete regiocontrol, relatively wide substrate scope, and high functional group tolerance. Mechanistic studies show that the reaction proceeds through the gold-catalyzed cascade oxidative C-H/C-H cross-coupling, cyclization and alkynylation.

Cu-catalysed direct C-H (hetero)arylation of [1,2,4]triazolo[4,3-a]pyridine to construct deep-blue-emitting luminophores.

Cu-catalysed direct C-H (hetero)arylation of [1,2,4]triazolo[4,3-a]pyridine has been accomplished for the first time to streamline the synthesis of 3-aryl-[1,2,4]triazolo[4,3-a]pyridines for screening blue-emitting materials. On this basis, the photophysical properties of the resulting compounds were systematically investigated, most of which exhibited excellent deep-blue emission with moderate to high quantum yields, photostability, air stability and thermal stability.

Rhodium(III)-Catalyzed ortho-Heteroarylation of Phenols through Internal Oxidative C-H Activation: Rapid Screening of Single-Molecular White-Light-Emitting Materials.

Reported herein is the first example of a transition-metal-catalyzed internal oxidative C-H/C-H cross-coupling between two (hetero)arenes through a traceless oxidation directing strategy. Without the requirement of an external metal oxidant, a wide range of phenols, including phenol-containing natural products, can undergo the coupling with azoles to assemble a large library of highly functionalized 2-(2-hydroxyphenyl)azoles. The route provides an opportunity to rapidly screen white-light-emitting materials. As illustrative examples, two bis(triphenylamine)-bearing 2-(2-hydroxyphenyl)oxazoles, which are difficult to access otherwise, exhibit bright white-light emission, high quantum yield, and thermal stability. Also presented is the first example of the white-light emission, in a single excited-state intramolecular proton transfer system, of 2-(2-hydroxyphenyl)azoles, thus highlighting the charm of C-H activation in the discovery of new organic optoelectronic materials.

Rhodium(III)-Catalyzed Activation of C(sp3)-H Bonds and Subsequent Intermolecular Amidation at Room Temperature.

Disclosed herein is a Rh(III)-catalyzed chelation-assisted activation of unreactive C(sp3)-H bonds, thus enabling an intermolecular amidation to provide a practical and step-economic route to 2-(pyridin-2-yl)ethanamine derivatives. Substrates with other N-donor groups are also compatible with the amidation. This protocol proceeds at room temperature, has a relatively broad functional-group tolerance and high selectivity, and demonstrates the potential of rhodium(III) in the promotive functionalization of unreactive C(sp3)-H bonds. A rhodacycle having a SbF6(-) counterion was identified as a plausible intermediate.