Intramolecular Dehydrogenative Photocyclization of N-Phenyl-1-naphthamides.

Here, we explore a dehydrogenative 6π photocyclization method for N-substituted naphthalene carboxamides, which can be conducted in air. This method employs DMSO as both the reaction solvent and oxidant while also stabilizing the excited state of the substrate. Furthermore, the addition of photosensitizer enables the reaction to proceed under a 440-445 nm LED source via energy transfer. The proposed mechanism is initially validated through DFT calculations.

Deconstructive Carboxylation of Activated Alkenes with Carbon Dioxide.

Carboxylation with carbon dioxide (CO2 ) represents one notable methodology to produce carboxylic acids. In contrast to carbon-heteroatom bonds, carbon-carbon bond cleavage for carboxylation with CO2 is far more challenging due to their inherent and less favorable orbital directionality for interacting with transition metals. Here we report a photocatalytic protocol for the deconstructive carboxylation of alkenes with CO2 to generate carboxylic acids in the absence of transition metals. It is emphasized that our protocol provides carboxylic acids with obviously unchanged carbon numbers when terminal alkenes were used. To show the power of this strategy, a variety of pharmaceutically relevant applications including the modular synthesis of propionate nonsteroidal anti-inflammatory drugs and the late-stage carboxylation of bioactive molecule derivatives are demonstrated.

Aroyl Fluorides as Bifunctional Reagents for Dearomatizing Fluoroaroylation of Benzofurans.

The 2,3-dihydrobenzofuran scaffold is widely found in natural products and biologically active compounds. Herein, dearomatizing 2,3-fluoroaroylation of benzofurans with aroyl fluorides as bifunctional reagents to access 2,3-difunctionalized dihydrobenzofurans is reported. The reaction that occurs by cooperative NHC/photoredox catalysis provides 3-aroyl-2-fluoro-2,3-dihydrobenzofurans with moderate to good yield and high diastereoselectivity. Cascades proceed via radical/radical cross-coupling of a benzofuran radical cation generated in the photoredox catalysis cycle with a neutral ketyl radical formed through the NHC catalysis cycle. The redox-neutral transformation exhibits broad substrate scope and high functional group compatibility. With anhydrides as bifunctional reagents, dearomatizing aroyloxyacylation of benzofurans is achieved and the strategy can also be applied to N-acylated indoles to afford 3-aroyl-2-fluoro-dihydroindoles.

[Essence of SUN Shen-tian's clinical features on acupuncture and moxibustion].

To summarize SUN Shen-tian's treatment ideas and clinical features. SUN applies meridian syndrome differentiation to the diagnosis and treatment of diseases; advocates that prevention and treatment of diseases should be regulated mind firstly; applies transcranial repetitive acupuncture combined modern cerebral cortex function positioning; emphasizes the application of multiple acupuncture methods and manipulation, and includes the meridian penetrating needling method, the flat needling and penetrating needling method, and the stagnant needle lifting method, pays attention to the importance of achieving qi and manipulation for the effect.

Benzylic C-H acylation by cooperative NHC and photoredox catalysis.

Methods that enable site selective acylation of sp3 C-H bonds in complex organic molecules are not well explored, particularly if compared with analogous transformations of aromatic and vinylic sp2 C-H bonds. We report herein a direct acylation of benzylic C-H bonds by merging N-heterocyclic carbene (NHC) and photoredox catalysis. The method allows the preparation of a diverse range of benzylic ketones with good functional group tolerance under mild conditions. The reaction can be used to install acyl groups on highly functionalized natural product derived compounds and the C-H functionalization works with excellent site selectivity. The combination of NHC and photoredox catalysis offers options in preparing benzyl aryl ketones.

Cooperative NHC and Photoredox Catalysis for the Synthesis of ß-Trifluoromethylated Alkyl Aryl Ketones.

Despite the great potential of radical chemistry in organic synthesis, N-heterocyclic carbene (NHC)-catalyzed reactions involving radical intermediates are not well explored. This communication reports the three-component coupling of aroyl fluorides, styrenes and the Langlois reagent (CF3 SO2 Na) to give various ß-trifluoromethylated alkyl aryl ketones with good functional group tolerance in moderate to high yields by cooperative photoredox/NHC catalysis. The alkene acyltrifluoromethylation proceeds via radical/radical cross coupling of ketyl radicals with benzylic C-radicals. The ketyl radicals are generated via SET reduction of in situ formed acylazolium ions whereas the benzylic radicals derive from trifluoromethyl radical addition onto styrenes.

Boosting Electrochemical Reduction of CO2 at a Low Overpotential by Amorphous Ag-Bi-S-O Decorated Bi0 Nanocrystals.

Bimetal-S-O composites have been rarely researched in electrochemical reduction of CO2 . Now, an amorphous Ag-Bi-S-O decorated Bi0 catalyst derived from Ag0.95 BiS0.75 O3.1 nanorods by electrochemical pre-treatment was used for catalyzing eCO2 RR, which exhibited a formate FE of 94.3 % with a formate partial current density of 12.52 mA cm-2 at an overpotential of only 450 mV. This superior performance was attributed to the attached amorphous Ag-Bi-S-O substance. S could be retained in the amorphous region after electrochemical pre-treatment only in samples derived from metal-S-O composites, and it would greatly enhance the formate selectivity by accelerating the dissociation of H2 O. The existence of Ag would increase the current density, resulting in a higher local pH, which made the role of S in activating H2 O more significantly and suppressed H2 evolution more effectively, thus endowing the catalyst with a higher formate FE at low overpotentials.

Photocarboxylation of Benzylic C-H Bonds.

The carboxylation of sp3-hybridized C-H bonds with CO2 is a challenging transformation. Herein, we report a visible-light-mediated carboxylation of benzylic C-H bonds with CO2 into 2-arylpropionic acids under metal-free conditions. Photo-oxidized triisopropylsilanethiol was used as the hydrogen atom transfer catalyst to afford a benzylic radical that accepts an electron from the reduced form of 2,3,4,6-tetra(9H-carbazol-9-yl)-5-(1-phenylethyl)benzonitrile generated in situ. The resulting benzylic carbanion reacts with CO2 to generate the corresponding carboxylic acid after protonation. The reaction proceeded without the addition of any sacrificial electron donor, electron acceptor or stoichiometric additives. Moderate to good yields of the desired products were obtained in a broad substrate scope. Several drugs were successfully synthesized using the novel strategy.

Site-Selective, Remote sp3 C-H Carboxylation Enabled by the Merger of Photoredox and Nickel Catalysis.

A photoinduced carboxylation of alkyl halides with CO2 at remote sp3 C-H sites enabled by the merger of photoredox and Ni catalysis is described. This protocol features a predictable reactivity and site selectivity that can be modulated by the ligand backbone. Preliminary studies reinforce a rationale based on a dynamic displacement of the catalyst throughout the alkyl side chain.

Controllable Isomerization of Alkenes by Dual Visible-Light-Cobalt Catalysis.

We report herein that thermodynamic and kinetic isomerization of alkenes can be accomplished by the combination of visible light with Co catalysis. Utilizing Xantphos as the ligand, the most stable isomers are obtained, while isomerizing terminal alkenes over one position can be selectively controlled by using DPEphos as the ligand. The presence of the donor-acceptor dye 4CzIPN accelerates the reaction further. Transformation of exocyclic alkenes into the corresponding endocyclic products could be efficiently realized by using 4CzIPN and Co(acac)2 in the absence of any additional ligands. Spectroscopic and spectroelectrochemical investigations indicate CoI being involved in the generation of a Co hydride, which subsequently adds to alkenes initiating the isomerization.

Ligand-Controlled Regioselective Hydrocarboxylation of Styrenes with CO2 by Combining Visible Light and Nickel Catalysis.

The ligand-controlled Markovnikov and anti-Markovnikov hydrocarboxylation of styrenes with atmospheric pressure of CO2 at room temperature using dual visible-light-nickel catalysis has been developed. In the presence of neocuproine as ligand, the Markovnikov product is obtained exclusively, while employing 1,4-bis(diphenylphosphino)butane (dppb) as the ligand favors the formation of the anti-Markovnikov product. A range of functional groups and electron-poor, -neutral, as well as electron-rich styrene derivatives are tolerated by the reaction, providing the desired products in moderate to good yields. Preliminary mechanistic investigations indicate the generation of a nickel hydride (H-NiII) intermediate, which subsequently adds irreversibly to styrenes.

General and Efficient Intermolecular [2+2] Photodimerization of Chalcones and Cinnamic Acid Derivatives in Solution through Visible-Light Catalysis.

[2+2] Photocycloaddition, for example, the dimerization of chalcones and cinnamic acid derivatives, is a unique strategy to construct cyclobutanes, which are building blocks for a variety of biologically active molecules and natural products. However, most attempts at the above [2+2] addition have focused on solid-state, molten-state, or host-guest systems under ultraviolet-light irradiation in order to overcome the competition of facile geometric isomerization of nonrigid olefins. We report a general and simple method to realize the intermolecular [2+2] dimerization reaction of these acyclic olefins to construct cyclobutanes in a highly regio- and diastereoselective manner in solution under visible light, which provides an efficient solution to a long-standing problem.

Identifying key intermediates generated in situ from Cu(II) salt-catalyzed C-H functionalization of aromatic amines under illumination.

Copper compounds involved in photocatalysis have recently spurred considerable interest for their novel transformations. However, mechanistic investigations are still in infancy. We find a new type of reaction, that is, Cu(II) salt-catalyzed C-H functionalization of aromatic amines triggered by visible light irradiation. An array of mechanistic observations, including high-resolution mass spectrometry, ultraviolet-visible absorption spectrum, electron spin resonance, x-ray absorption near-edge structure, and density functional theory calculation, have identified the key intermediates generated in situ in the transformation. Integration of single-electron transfer, singlet oxygen (1O2), and new absorption species, intermediate I and intermediate II formed in situ from Cu(II) salts and substrate amines or imines, respectively, is responsible for the N-H and C-H bond activation of secondary amines to couple with nucleophiles in air, thereby leading to the formation of quinoline, indolo[3,2-c]quinoline, ß-amino acid, and 1,4-dihydropyridine derivatives in moderate to good yields under visible light irradiation at room temperature.

Carboxylation of Aromatic and Aliphatic Bromides and Triflates with CO2 by Dual Visible-Light-Nickel Catalysis.

We report the efficient carboxylation of bromides and triflates with K2 CO3 as the source of CO2 in the presence of an organic photocatalyst in combination with a nickel complex under visible light irradiation at room temperature. The reaction is compatible with a variety of functional groups and has been successfully applied to the synthesis and derivatization of biologically active molecules. In particular, the carboxylation of unactivated cyclic alkyl bromides proceeded well with our protocol, thus extending the scope of this transformation. Spectroscopic and spectroelectrochemical investigations indicated the generation of a Ni0 species as a catalytic reactive intermediate.

A sustainable synthesis of 2-aryl-3-carboxylate indolines from N-aryl enamines under visible light irradiation.

With visible light irradiation of a catalytic amount of Ir(ppy)3 at room temperature, a number of N-aryl enamines were transformed into their corresponding indoline products in good to excellent yields without requiring any extra additives. This is the first example of the synthesis of indolines via the intramolecular cyclization of enamines under visible light irradiation.

Benzene C-H Etherification via Photocatalytic Hydrogen-Evolution Cross-Coupling Reaction.

Aryl ethers can be constructed from the direct coupling between the benzene C-H bond and the alcohol O-H bond with the evolution of hydrogen via the synergistic merger of photocatalysis and cobalt catalysis. Utilizing the dual catalyst system consisting of 3-cyano-1-methylquinolinum photocatalyst and cobaloxime, intermolecular etherification of arenes with various alcohols and intramolecular alkoxylation of 3-phenylpropanols with formation of chromanes are accomplished. These reactions proceed at remarkably mild conditions, and the sole byproduct is equivalent hydrogen gas.

Photocatalysis with Quantum Dots and Visible Light: Selective and Efficient Oxidation of Alcohols to Carbonyl Compounds through a Radical Relay Process in Water.

Selective oxidation of alcohols to aldehydes/ketones has been achieved with the help of 3-mercaptopropionic acid (MPA)-capped CdSe quantum dot (MPA-CdSe QD) and visible light. Visible-light-prompted electron-transfer reaction initiates the oxidation. The thiyl radical generated from the thiolate anion adsorbed on a CdSe QD plays a key role by abstracting the hydrogen atom from the C-H bond of the alcohol (R1 CH(OH)R2 ). The reaction shows high efficiency, good functional group tolerance, and high site-selectivity in polyhydroxy compounds. The generality and selectivity reported here offer a new opportunity for further applications of QDs in organic transformations.

Influence of Surface Chemistry on Adhesion and Osteo/Odontogenic Differentiation of Dental Pulp Stem Cells.

The complex interaction between extracellular matrix and cells makes the design of materials for dental regeneration challenging. Chemical composition is an important characteristic of biomaterial surfaces, which plays an essential role in modulating the adhesion and function of cells. The effect of different chemical groups on directing the fate of human dental pulp stem cells (hDPSCs) was thus explored in our study. A range of self-assembled monolayers (SAMs) with amino (-NH2), hydroxyl (-OH), carboxyl (-COOH), and methyl (-CH3) modifications were prepared. Proliferation, morphology, adhesion, and differentiation of hDPSCs were then analyzed to demonstrate the effects of surface chemical groups. The results showed that hDPSCs attached to the -NH2 surface displayed a highly branched osteocyte-like morphology with improved cell adhesion and proliferation abilities. Moreover, hDPSCs cultured on the -NH2 surface also tended to obtain an increased osteo/odontogenesis differentiation potential. However, the hDPSCs on the -COOH, -OH, and -CH3 surfaces preferred to maintain the mesenchymal stem cell-like phenotype. In summary, this study indicated the influence of chemical groups on hDPSCs in vitro and demonstrated that -NH2 might be a promising surface modification strategy to achieve improved biocompatibility, osteoconductivity/osteoinductivity, and osseointegration of dental implants, potentially facilitating dental tissue regeneration.

Tracking Co(I) Intermediate in Operando in Photocatalytic Hydrogen Evolution by X-ray Transient Absorption Spectroscopy and DFT Calculation.

X-ray transient absorption spectroscopy (XTA) and optical transient spectroscopy (OTA) were used to probe the Co(I) intermediate generated in situ from an aqueous photocatalytic hydrogen evolution system, with [RuII(bpy)3]Cl2·6H2O as the photosensitizer, ascorbic acid/ascorbate as the electron donor, and the Co-polypyridyl complex ([CoII(DPA-Bpy)Cl]Cl) as the precatalyst. Upon exposure to light, the XTA measured at Co K-edge visualizes the grow and decay of the Co(I) intermediate, and reveals its Co-N bond contraction of 0.09 ± 0.03 Å. Density functional theory (DFT) calculations support the bond contraction and illustrate that the metal-to-ligand π back-bonding greatly stabilizes the penta-coordinated Co(I) intermediate, which provides easy photon access. To the best of our knowledge, this is the first example of capturing the penta-coordinated Co(I) intermediate in operando with bond contraction by XTA, thereby providing new insights for fundamental understanding of structure-function relationship of cobalt-based molecular catalysts.

Radical Addition of Hydrazones by α-Bromo Ketones To Prepare 1,3,5-Trisubstituted Pyrazoles via Visible Light Catalysis.

A novel efficient tandem reaction of hydrazones and α-bromo ketones is reported for the preparation of 1,3,5-trisubstituted pyrazoles by visible light catalysis. In this system, the monosubstituted hydrazones show wonderful reaction activity with alkyl radicals, generated from α-bromo ketones. A radical addition followed by intramolecular cyclization affords the important pyrazole skeleton in good to excellent yields. This efficient strategy under mild conditions with wide group tolerance provides a potential approach to the 1,3,5-trisubstituted pyrazoles.