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The asymmetric carbenoid C-H insertion of 3-diazooxindoles into 1,4-cyclohexadiene has been accomplished in the presence of chiral bis-(imidazoline) NCN pincer iridium(III) complexes as the catalysts. With a catalyst loading of 0.5 mol%, the reactions proceeded smoothly at 0 °C to afford a variety of chiral 3-substituted oxindoles in good yields with moderate to excellent enantioselectivities (up to 99% ee). The protocol exhibits good functional group tolerance with respect to 3-diazooxindoles and is readily scaled up to 2 mmol scale without any loss in activity and enantioselectivity. Density functional theory (DFT) calculations have been performed to better understand the reaction mechanism and to explain the stereochemical outcome of the reactions.

A facile and sustainable approach for the amination of benzothiazoles with KSeCN using iodine as the catalyst in water has been disclosed under transition-metal free conditions. The reaction proceeded smoothly to afford various primary 2-amino benzothiazoles in up to 96% yield. A series of control experiments were performed, suggesting a ring-opening mechanism was involved via a radical process. This protocol provides efficient synthesis of primary 2-aminobenzothiazoles

A regioselective arylation of aliphatic N-fluorosulfonamides with imidazopyridines enabled by breaking of N-F and α C(sp3)-H bond to form C-N and C-C bonds was described. With CuCl as the catalyst, a radical mechanism was proposed to produce N-arylated aliphatic sulfonamides via a N radical intermediate. Importantly, under acidic conditions, an in situ generated imine was the possible intermediate, which was trapped by imidazopyridines to form α C(sp3)-H arylated aliphatic sulfonamides. The current protocol featured a broad substrate scope, tunable reaction conditions, operational convenience, and good regioselectivity.

An iron-mediated highly selective C-H sulfonylmethylation of aniline derivatives with p-toluenesulfonylmethyl isocyanide in a mixture solvent of H2O and PEG400 under an Ar atmosphere has been realized. This transformation proceeds with operational convenience, use of earth-abundant metal catalyst and nontoxic media, broad substrate scope, and good functional group tolerance. The current methodology could be applied to the regioselective C-H sulfonylmethylation of indolines, tetrahydroquinolines, and tertiary anilines.

Herein, we disclose an efficient cobalt-catalyzed three-component coupling of benzamides, diazo compounds, and tert-butyl hydroperoxide, which provides an efficient approach to construct C(sp2)-C(sp3) and C-O bonds in one-pot accompanied with C-H activation. This protocol features low catalyst loading (4 mol %), the avoidance of additives, and excellent functional group compatibility, providing three-component coupling adducts with high yields under mild conditions (up to 88%). Mechanism studies show that the reaction may involve a radical process.

A metal-organic photoinduced electron transfer (PET) supramolecular nanoarchitecture comprised of Ru(II) bis(terpyridine)-modified pillar[5]arene (electron acceptor) and triazole triphenylamine amyl cyanide (electron donor) has been designed and constructed. Through the comparison of diverse solvents and acceptors, the two conditions, i.e., modification of pillar[5]arene to donor and weak polar solvent are benefit for the occurrence of “efficient PET” because of shorter D-A distance in the presence of pillar[5]arene. Crucially, the fluorescence and PET process of the supramolecular assembly could be further modulated by solvent conversion and another competitive guest. The study provides a supramolecular method to design and construct tunable PET systems and PET-based smart materials.

A new method for the direct and stereoselective synthesis of 3-substituted isoindolinones via Rh(III)-catalyzed chiral N-sulfinyl amide directed asymmetric [4 + 1] annulation of benzamides with acrylic esters has been developed. The reaction proceeded through an oxidative C–H olefination and a subsequent cyclization by intramolecular aza-Michael addition, producing a series of diastereoisomeric chiral isoindolinones (20 examples) in generally good yields with a dr value up to 5.5 : 1. The absolute configurations of the newly formed C-stereocenters in the major and minor diastereomers of the catalysis product have been determined by X-ray crystal diffraction analysis to be S and R, respectively. The separation of the major diastereoisomers from the catalysis products and subsequent removal of the N-sulfinyl chiral auxiliary afforded enantiomerically pure (S)-isoindolinones. The application of the obtained (S)-isoindolinones in the synthesis of several biologically active isoindolinones such as (S)-PD172938, (S)-pazinaclone and (S)-pagoclone is presented.

The direct C(sp3)-H bond amination has become a hot topic due to its high efficiency in converting the C(sp3)-H bond to the C-N bond. Herein, we report an efficient intramolecular C(sp3)-H bond sulfonamidation under metal-free conditions, which provides a straightforward method for the synthesis of 5-membered cyclic sulfonamides (benzosultams). This protocol avoids the use of metal catalysts, oxidants, and any additives. Mechanistic experiments and the DFT calculations, revealed that the reaction proceeds through a proton transfer coupled with the SN2 (PTSN2) manner, which is different from the other pathways.

A NaOH-mediated sustainable synthesis of functionalized quinoxalines is disclosed via redox condensation of o-nitroamines with diols and α-hydroxy ketones. Under optimized conditions, various o-nitroamines and alcohols are well tolerated to generate the desired products in 44-99% yields without transition metals and external redox additives.

A Ru(II)-catalyzed bisallylation of imidazopyridines with vinylcyclopropanes or vinyl cyclic carbonate has been successfully realized. Notably, pharmacophore imidazopyridine was utilized as an intrinsic directing group, which gave access to value-added bisallylated products in high yields via double tandem C-H and C-C/C-O activation. The current methodology was featured with broad substrate scope, good functional group compatibility, and operational simplicity.

An efficient Cp*Rh(III)-catalyzed direct acylmethylation of 2H-indazoles with sulfoxonium ylides has been realized under air atmosphere via chelation-assisted strategy. This protocol enables a regioselective access to a variety of ortho-acylmethylated 2-phenylindazole derivatives in moderate to good yield, which has the advantages of broad substrate scope, good functional group tolerance, and operational convenience. The H/D exchange experiment reveals that a reversible cleavage of C-H bond might not be the rate-limiting step in this transformation.

This microreview is devoted to the arylindazole C–H functionalization methodologies. The latest selected examples covering 2016–2020 period on the synthesis of indazolo-[2,3-a]quinolines and other heterocycles by transition metal catalyzed C–H activation reactions are summarized. In particular, novel transition metal catalytic systems and differently functionalized synthons utilized for the synthesis of indazolo[2,3-a]quinolines are mainly discussed in this review.

A Rh(III)-catalyzed direct cyanation of 2H-indazoles with N-cyano-N-phenyl-p-toluenesulfonamide has been realized via a chelation-assisted strategy. The methodology enables regioselective access to...

Bis(3-indolyl)methanes are well-known natural products with a broad range of important biological functions including cancer cell growth inhibition and antimicrobial activity. Incorporation of a trifluoromethyl group is known to have a profound effect on the parent compound's biological activities. Here, an efficient method for the synthesis of chiral trifluoromethylated bis(3-indolyl)methanes via a catalytic asymmetric Friedel-Crafts (F-C) alkylation reaction has been established. Both enantiomers of the catalysis products can be obtained by tuning the chiral substituents of the catalyst. With 5 mol % of the Ni(II)/(imidazoline-oxazoline) complex as the catalyst, the F-C reaction of indoles with β-CF

A sustainable and transition metal-free approach for C3 chalcogenation and chalcogenocyanation of imidazopyridines with KXCN (X = S or Se) has been developed under mild conditions. Importantly, this reaction was performed in the presence of catalytic iodine in aqueous medium, which afforded either chalcogenated or chalcogenocyanated imidazopyridines under temperature control. The current protocol featured a broad substrate scope, transition metal-free and organic solvent-free conditions, operational convenience, and gram-scale production.

A series of chiral NCN pincer iridium(III) complexes 2a–h with bis(imidazolinyl)phenyl ligands were synthesized via the central aryl C2–H bond activation of the 1,3-bis(2′-imidazolinyl)benzene liga...

The earth-abundant cobalt-catalyzed anti-Markovnikov hydroalkylation of unactivated alkenes with oxime esters was achieved by introducing an 8-aminoquinoline directing group on the alkenes. The catalytic system, consisting of commercially available Co(acac)3 and PhMeSiH2, enables the construction of unfunctionalized C(sp3)-C(sp3) bonds and features exclusive anti-Markovnikov selectivity, good functional group tolerance, and the avoidance of an extra ligand, oxidant, or base. Mechanistic insight into this new catalytic system indicates the involvement of both alkyl radical and cobalt hydride intermediates.

A palladium-catalyzed δ-selective reductive Heck reaction of 4-pentenoic acid derivatives bearing an 8-aminoquinoline directing group with aryl iodides and bromides has been developed. The reactions were carried out by using 5–10 mol% of Pd(OAc)2 as the catalyst without the addition of external ligand in the presence of K3PO4 base in EtOH at 100 °C under air. Under these conditions both terminal and internal unactivated alkenes reacted smoothly with various aryl iodides and bromides to give a wide variety of δ-aryl pentanoic acid derivatives as single regioisomeric products in moderate to good yields. Deuterium-labeling experiments suggest that the ethanol serves as the hydride source in the reaction.

The syntheses of 4'-substituted chiral 2,2':6',2″-terpyridine (tpy) ligands with predetermined configurations and directionalities are rather limited in the supramolecular chemistry field. In this study, a carbazole-linked ditopic chiral ligand

Two different types of new phosphinamide α -amino ester derivatives have been prepared in moderate to high yields via ruthenium(II) and rhodium(III)-catalyzed ortho -C-H functionalization under microwave irradiation. Specifically, the ortho -alkenylated phosphinamides were produced through coupling of phosphinamides containing an α -substituted or α , α -disubstituted α -amino ester with internal alkynes under ruthenium catalysis. In contrast, Ru and the more effective Rh-catalyzed coupling of the α -unsubstituted glycine ester phosphinamide with alkynes resulted in formation of oxidative annulation products, phosphaisoquinolin-1-ones. The developed methods feature the use of easily accessible starting materials, short reaction time, exclusive E -stereoselectivity (for ortho -alkenylation) and good functional group tolerance. The alkenylation reaction was readily scaled up to gram scale. Furthermore, the obtained alkenylated phosphinamide could be transformed into P-containing dipeptides through hydrolysis of the ester group in the catalysis product and subsequent condensation with an α -amino ester.

An iron-catalyzed C–H sulfonylmethylation of indoles in water–PEG400 has been developed using p-toluenesulfonylmethyl isocyanide. This protocol enables direct regioselective construction of Csp2–Csp3 bond at the C3 position of indoles with a broad range of substrate compatibility in moderate to good yields, which is cost-effective and environmentally friendly.

A series of unsymmetrical NNN′ ruthenium(II) complexes supported by a tridentate bipyridyl imidazoline ligand with variable steric hindrance (2a–c; R1 = tBu, iPr, or Bn) and electronic effect (2d–h; R2 = H, CH3, OCH3, Br, or NO2) were prepared. The molecular structures of ligands 1f and 1g, and Ru complex 2a were further determined by X-ray single-crystal diffraction. The catalytic activity of these eight complexes for α-alkylation of nitriles with alcohols was evaluated, which could be controlled by the substituents on the imidazoline moiety. Ru complex 2h bearing a strong electron-withdrawing group (R2 = NO2) demonstrated the highest catalytic activity, with alkylated nitriles achieved in up to 97% yield.

The first nickel(II)-catalyzed direct sulfuration/annulation of C(sp2)–H bonds with elemental sulfur has been achieved by using 2-amino alkylbenzimidazole (MBIP-amine) as a N,N-bidentate directing group. This strategy tolerates a wide range of functional groups, furnishing structurally diverse benzoisothiazolone derivatives with benzimidazole skeletons in moderate to excellent yields in a simple and efficient way.

A method for Cu-mediated direct ortho-C–H sulfonylation of benzoic acid derivatives was developed by employing a PyO-directing group. For the first time, TosMIC could act as a sulfonyl source instead of sulfonyl chlorides or sulfinate salts. This protocol featured cheap metal catalysis, broad functional group compatibility and easy handling nature. Moreover, the PyO-directing group could be efficiently removed in one step.

The first enantioselective Michael addition of 2-acetyl azaarenes to β-CF3-β-(3-indolyl)nitroalkenes has been successfully achieved in the presence of a Co(II)/(imidazoline-oxazoline) complex as the catalyst. The reaction affords a series of CF3- and 3-indole-containing adducts featuring a trifluoromethylated all-carbon quaternary stereocenter in good to excellent yields (up to 99%) and enantioselectivities (up to 96% ee). Furthermore, the functional groups in the adducts including C═O, NO2, and the azaarene provide a large variety of useful transformations, leading to the formation of valuable intermediates such as optically active secondary alcohol, pyrroline, ester, and pyrrolidinone which all contain a 3-substituted indole and a trifluoromethylated all-carbon quaternary stereocenter.

An efficient protocol has been accomplished for the synthesis of quaternary α-aminosuccinimides in toluene medium involving 2-phenylimidazo[1, 2-a]pyridine in a one-pot reaction promoted by Ferric Nitrate at 120 °C. The protocol presented herein, is for the first time, via a novel transformation where Ferric Nitrate promotes imidazo[1,2-a]pyridine structural metamorphosis to the title compound quaternary succinimides. High compatibility, easy work-up, and excellent yields are the advantages of this protocol. The quaternary α-aminosuccinimides are expected to have great potential in synthesizing quaternary α-amino acids and applications in medicinal chemistry.

Blue-light-mediated cyclopropanation of indoles with aryl(diazo)acetates has been developed. The salient features of this strategy are that it is metal-free, operationally simple and atom-efficient, and that it uses an environmentally friendly energy source. In this protocol, blue light was employed as the sole energy source for the transformation. A variety of cyclopropane-fused indoline compounds was obtained in moderate to excellent yields and high diastereoselectivities under mild conditions.

A new traceless directing group, 2-(hydroxymethyl)pyridine, has been reported for the Cp*-free cobalt-catalyzed C-H activation/annulation reaction to synthesize isoquinolinones. The reaction exhibits good functional group tolerance, affording products in good to excellent isolated yields under mild conditions. Notably, the directing group can be removed directly in situ along the catalytic process.

A cobalt-catalyzed C(sp2)–H alkoxylation of 1-naphthylamine derivatives has been disclosed, which represents an efficient approach to synthesize aryl ethers with broad functional group tolerance. It is noteworthy that secondary alcohols, such as hexafluoroisopropanol, isopropanol, isobutanol, and isopentanol, were well tolerated under the current catalytic system. Moreover, a series of biologically relevant fluorine-aryl ethers were easily obtained under mild reaction conditions after the removal of the directing group.

A strategy for the synthesis of isoxazolidine/1,2-oxazinane-fused isoquinolin-1(2H)-ones from alkyne-tethered N-alkoxyamides is described, in which cheap Mn(acac)2 is used as a catalyst to facilitate a radical cascade annulation. The method features mild conditions, additive-free reaction and broad substrate scope. It is the first example via manganese/air catalytic systems to construct isoquinolin-1(2H)-one heterocycles.

Selective monoarylation of naphthylpyrimidines with a variety of aryl chlorides through C–H bond activation in water was achieved by using a water-soluble [RuCl2-(η6-PhOCH2CH2OH)]2/phosphine catalytic system. The monoarylation occurred at the C-2 carbon of the naphthalene moiety, and selectively polysubstituted naphthylpyrimidines were obtained by a one-pot reaction involving a subsequent hetarylation with 2-pyridyl chlorides.

A series of palladium(II) and nickel(II) complexes based on unsymmetrical chiral (imidazolinyl)aryl NHC ligands are reported. The new ligand presursors 3a–g were prepared from commercially available 3-bromobenzoic acid, in which the carboxyl and bromo functionalities were converted to chiral imidazoline and NHC moieties, respectively, in three steps. Treatment of 3a–g with Pd(OAc)2 in dimethylacetamide in the presence of NaOAc, followed by addition of LiCl, gave the seven palladium(II) pincer complexes 4a–g via direct aryl C–H activation. Likewise, the six nickel(II) pincer complexes 5a–f were obtained by reacting 3a–f with anhydrous NiCl2. All of the ligand precursors and pincer complexes are bench-stable and were fully characterized. The absolute configurations of palladium complexes 4a,c and 5e were further determined by X-ray diffraction. Finally, Pd pincer complex catalyzed asymmetric Friedel–Crafts alkylation and aza-Morita–Baylis–Hillman reactions were briefly assessed.

The PCN pincer Pd(II) complexes 4a–c with (phosphinito)aryl benzimidazole ligands were conveniently synthesized by one-pot phosphorylation/palladation reaction of a (2-benzimidazolyl)-containing m-phenol derivative 3. The three complexes were well characterized by spectroscopic methods, elemental analysis and their molecular structures were further determined by X-ray single-crystal diffraction. The Pd(II) center in each complex adopts a typical distorted-square-planar geometry. With a catalyst loading of 0.25–0.5 mol%, complex 4a could effectively catalyze C H arylation of benzothiazole, benzoxazole and thiazole with various aryl iodides in the presence of CuI as a cocatalyst.

Novel iodine-induced sulfonylation and sulfenylation of imidazopyridines have been described using sodium sulfinates as the sulfur source. This strategy enables highly selective difunctionalization of imidazo[1,2-a]pyridine to access sulfones and sulfides in good yields. A wide range of substrates and functional groups were well-tolerated under optimized conditions. Moreover, control experiments have been conducted, indicating a radical pathway involved in the reaction mechanisms.

The zinc complex ZnE containing two 2-(2′-hydroxyphenyl)-1-ethyl-4-hydroxybenzimidazole (EtL) ligands has been designed and synthesized. The zinc ion acts as a spacer linking the two coordinated EtL, between which intramolecular hydrogen bonds form. Upon excitation, in addition to a weak emission at 399 nm, ZnE exhibits strong excited-state intramolecular proton-transfer (ESIPT) emission with a maximum at 479 nm with a large Stokes shift (8449 cm–1) in tetrahydrofuran solution. Importantly, the ESIPT in ZnE also takes place in the powder form, resulting in dual emission (407 and 490 nm) with total photoluminescence quantum yields (Φ) of 0.16. The results of quantum calculations suggest that the ESIPT fluorescence is based on a zwitterionic excited-state species resulting from a single proton transfer between the ligands.

A Pd(II)-catalyzed acetoxylation of 2H-indazoles with phenyliodine (III) diacetate (PIDA) has been successfully developed. Notably, pharmacophore 2H-indazole was utilized as an inherent directing group to access ortho-acetoxylated arylindazoles in moderate to high yields. The representative acetoxylated indazole could further undergo hydrolysis to afford the corresponding hydroxylated product.

Inorganic perovskite oxide photosensitizer have shown versatile practical applications, owing to fruitful chemistries of photoelectric materials. This work reports a straightforward and general protocol via the use of Co/Ba co-doped KNbO3 (KBCNO) photosensitizer coupled with TiO2 nanorods to boost photoelectricity property. In the representative system, KBCNO with different doping concentrations and TiO2 nanorods were used as photosensitizer and electron transfer layer, respectively. The synthetic process implicated that KBCNO with various concentration prepared by pulsed laser deposition technique and TiO2 nanorods were used as an active optical absorption layer and electrode, and the specific physicochemical, optical characterization and photoelectrochemical (PEC) performance were all discussed in detail in the detection of the obtained photoelectrodes. This work is also an effective extension of previous studies on the category of inorganic perovskite oxide photosensitizers, which has not been reported by other research group. Given that KNbO3-based compounds can be easily obtained in abundance and variety, this work enjoys great advantages in PEC performance of numerous other inorganic perovskite oxide photosensitizer.