Metal-free, regioselective, visible light activation of 4CzIPN for the arylation of 2H-indazole derivatives

Catalyst-free photoarylation of 2-aryl-2H-indazoles by carbon-iodine bond activation

A photocatalyst-free visible-light induced arylation of 2-aryl-2H-indazoles with aryl iodides has been developed for the first time to produce 3,2-diaryl-2H-indazoles in good to moderate yields. In this transformation, potassium tert-butoxide acts as an activator of the C-I bond and also as a scavenger of in situ generated HI in the reaction. This method exhibits high functional group tolerance with a wide substrate scope and it has been successfully applied to the synthesis of liver X receptor agonists and also for fluorescent probes. This is the first report on the photoarylation of 2-arylindazoles at the C3-position with aryl iodides under catalyst-free conditions.

Visible-light promoted oxidative annulation of 2-naphthols with phenylglyoxal monohydrates toward hydroxy-naphthofuranone and its derivatives

A highly efficient and innovative method involving base-mediated oxidative annulation between 2-naphthols and phenylglyoxal monohydrate under visible light irradiation has been successfully developed. This method leads to the formation of oxygen-containing heterocyclic compounds, particularly hydroxy-naphthofuranone derivatives, encompassing a unique quaternary carbon center. An X-ray diffraction study has unambiguously confirmed the structure of one such derivative. In particular, water molecules in this reaction serve various functions as a solvent, reagent, and additive, with the conversion of the process found to be influenced by the volume of water present. This atom-economical approach demonstrates tolerance for different substituents in both phenylglyoxal monohydrate and 2-naphthol, enabling the synthesis of a variety of naphthofuranones in satisfactory to good yields. The formation of a naphthofuranium cationic intermediate under acidic circumstances enables the formation of C-C or C-O bonds with a wide range of aromatic or alcoholic nucleophilic partners. Furthermore, the identification and generation of pinacol-type starting precursors from these naphthofuranone derivatives enable the synthesis of highly regioselective naphthofuran derivatives.

Diindolocarbazole-Based Rigid Donor-Acceptor TADF Molecules for Energy and Electron Transfer Photocatalysis

The design and synthesis of four twisted donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) molecules CBZ-IQ, CBZ-2FIQ, DI-IQ and DI-2FIQ is reported in this work based on diindolocarbazole (DI) and phenyl carbazole as donor and indoloquinoxalines as acceptor. These compounds serve as photocatalysts for organic transformations. Theoretical calculations and experimental data showed reasonable singlet and triplet energy gaps of 0.17-0.26 eV for all compounds. All molecules showed increase in fluorescence quantum yields after degassing the solution and the transient photoluminescence decay showed two components: shorter prompt components (11.4 ns to 31 ns) and longer delayed components (36.4 ns to 1.5 μs) which further indicate the occurrence of TADF process. Cyclic voltammetry studies indicated well-suited excited state redox potentials of all compounds to catalyze organic transformations such as heteroarene arylation. Accordingly, photocatalytic C-H arylation of heteroarenes were performed using these compounds with excellent isolated yields of upto 80 %. Due to their suitable efficient triplet energy levels, all the emitters were also employed as energy transfer photocatalysts in E to Z isomerization of stilbene with the excellent conversion of ~90 %.

Research status and prospects of organic photocatalysts in algal inhibition and sterilization: a review

An increasing amount of sewage has been discharged into water bodies in the progression of industrialization and urbanization, causing serious water pollution. Meanwhile, the increase of nutrients in the water induces water eutrophication and rapid growth of algae. Photocatalysis is a common technique for algal inhibition and sterilization. To improve the utilization of visible light and the conversion efficiency of solar energy, more organic photocatalytic materials have been gradually developed. In addition to ultraviolet light, partial infrared light and visible light could also be used by organic photocatalysts compared with inorganic photocatalysts. Simultaneously, organic photocatalysts also exhibit favorable stability. Most organic photocatalysts can maintain a high degradation rate for algae and bacteria after several cycles. There are various organic semiconductors, mainly including small organic molecules, such as perylene diimide (PDI), porphyrin (TCPP), and new carbon materials (fullerene (C60), graphene (GO), and carbon nanotubes (CNT)), and large organic polymers, such as graphite phase carbon nitride (g-C3N4), polypyrrole (PPy), polythiophene (PTH), polyaniline (PANI), and polyimide (PI). In this review, the classification and synthesis methods of organic photocatalytic materials were elucidated. It was demonstrated that the full visible spectral response (400-750 nm) could be stimulated by modifying organic photocatalysts. Moreover, some problems were summarized based on the research status related to algae and bacteria, and corresponding suggestions were also provided for the development of organic photocatalytic materials.

Cu-Catalyzed Regioselective C-H Amination of 2H-Indazoles for the Synthesis of Indazole-Containing Indazol-3(2H)-ones

A copper-catalyzed C3 amination of 2H-indazoles with 2H-indazoles and indazol-3(2H)-ones under mild conditions was developed. A series of indazole-containing indazol-3(2H)-one derivatives were produced in moderate to excellent yields. The mechanistic studies suggest that the reactions probably proceed through a radical pathway.

Visible-Light-Promoted Direct C3-H Cyanomethylation of 2H-Indazoles

The efficient visible-light-promoted cyanomethylation of 2H-indazoles in the presence of Ir(ppy)₃ as the photocatalyst and bromoacetonitrile as the cyanomethyl radical source was achieved under mild conditions, providing a series of C3-cyanomethylated derivatives in good yields.

Carbazole-based photocatalyst (4CzIPN) for novel donor-acceptor (D-A) fluorophore-catalyzed visible-light-induced photosynthesis of 3,4-dihydropyrimidin-2-(1H)-ones/thiones via a proton-coupled electron transfer (PCET) process

Based on the Biginelli reaction of β-ketoesters, arylaldehydes, and urea/thiourea, we created a green radical synthesis procedure for 3,4-dihydropyrimidin-2-(1H)-ones/thiones. A PCET (proton-coupled electron transfer) photocatalyst was used in an ethanol solution in an air environment and at room temperature and visible light to provide a renewable energy source. In this study, we seek to create a novel donor-acceptor (D-A) fluorophore that is affordable and widely available. The carbazole-based photocatalyst (4CzIPN), in addition to its time-saving capabilities and simplicity of use, exhibits excellent yields, is energy-efficient, and is ecologically friendly. This makes it possible to track the evolution of environmental and chemical factors throughout time. To determine the turnover number (TON) and turnover frequency (TOF) of 3,4-dihydropyrimidin-2-(1H)-ones/thiones, a study was done. Gram-scale cyclization demonstrates that it may be used in industry effectively.

Visible light-promoted transition metal-free direct C3-carbamoylation of 2H-Indazoles

We reported a general transition metal-free transformation to access C3-carbamoylated 2H-indazoles via visible light-induced oxidative decarboxylation coupling, in the presence of oxamic acids as the coupling sources, 4CzIPN as the photocatalyst, and Cs2CO3 as the base. The great application potential of this mild condition is highlighted by the late-stage modification of drugs, N-terminal modification of peptides, and the good antitumor activity of the novel desired product.

Visible light-induced functionalization of indazole and pyrazole: a recent update

Indazole and pyrazole are renowned as a prodigious class of heterocycles having versatile uses in medicinal as well as industrial chemistry. Considering sustainable approaches, recently, photocatalysis has become an indispensable tool in organic chemistry due to its application for the activation of small molecules and the use of a clean energy source. In this review, we have highlighted the use of metal-based photocatalysts, organic photoredox catalysts, energy transfer photocatalysts and electron-donor-acceptor complexes in the functionalization of indazole and pyrazole. This perspective is arranged based on the types of functionalization reactions on indazole and pyrazole. A detailed discussion regarding the reaction mechanism of each reaction is given to provide a comprehensive guide to the reader. Finally, a summary of existing challenges and the future outlook towards the development of efficient photocatalytic methods for functionalization of these heterocycles is also presented.

Visible-light-induced Direct 3-Ethoxycarbonylmethylation of 2-Aryl-2H-Indazoles in Water

A visible-light-driven Rhodamine B-catalyzed transition-metal-free 3-ethoxycarbonylmethylation of 2-aryl-2H-indazoles and imidazo[1,2-a]pyridines (40 examples) using commercially available α-bromoesters was realized in water. This protocol features sustainable, operational simplicity, mild reaction conditions, and...

Visible light-promoted, photocatalyst-free decarboxylative alkylations of 2H-indazoles via electron donor-acceptor-complex activation

A transition-metal-free and traditional dye-free visible light-driven directly alkylation of 2-aryl-2H-indazoles was developed in the catalytic of an electron donor-acceptor (EDA) complex among alkyl N-hydroxyphthalimide (NHPI) esters, triphenylphosphine (PPh3), and...