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The green synthesis of medicines with an indazole skeleton has gained significant attention in recent years. Sustainable and environmentally friendly approaches for the synthesis of this important class of heterocyclic compounds from azobenzenes are attractive but rare. In this work, a series of neat, fast, and efficient reactions are well developed as a notable methodology for the photo-organic synthesis of indazoles. Metal and hydrogen source-free direct deoxygenative cyclization of o-carbonyl azobenzene under visible light is achieved through a new mechanism with huge potential in reduction cyclization reactions. Most examples are shown to give the corresponding 2H-indazole products in excellent yields, demonstrating that the present reaction has a wide substrate scope and good functional group tolerance. [ABSTRACT FROM AUTHOR]

As fluorine atoms significantly strengthen the metabolic stability and bioavailability of organic molecules, benzyl fluoride is found as an essential skeleton in pharmaceuticals or biologically active molecules. Here, we employ sulfur hexafluoride (SF6) as an efficient fluorinating reagent, achieving nucleophilic fluorination of widely available benzyl alcohols under visible LED light irradiation with a low dosage of photocatalyst 4CzIPN. The reaction is compatible with several substrate backbones and is not air- or moisture-sensitive, realizing the degradation and utilization of SF6, a potent greenhouse gas resource. [ABSTRACT FROM AUTHOR]

Contemporary methods for synthesizing thioesters often necessitate expensive catalysts and harsh conditions, making their synthesis from chemical feedstocks challenging. Herein, we report a sustainable metal-, photocatalyst-, and oxidant-free electron donor–acceptor (EDA) mediated synthesis of thioesters via site-selective C–H functionalization using aryl sulfonium salts (acceptor) with potassium thioacid salts (donor) under visible light irradiation. Our approach enables rapid access to thioesters from a wide variety of arenes, including pharmaceutical and agrochemical compounds, as well as a diverse range of alkyl, aryl, and heteroaryl potassium thioacid salts with excellent efficiency and regioselectivity. Mechanistic studies supported the formation of an EDA-complex, and radical trapping experiments corroborated the involvement of a radical-based mechanism for the product formation. Moreover, our method demonstrates excellent atom economy and E-factor scores, which are considered excellent in terms of safety, economic and ecological yardsticks. [ABSTRACT FROM AUTHOR]

Herein, an operationally simple and mild protocol for defluorinative alkylation and arylation between thianthrenium salts and α-trifluoromethyl alkene with visible light to afford gem-difluoroolefins has been developed. The main feature of this method is avoiding the use of a metal photocatalyst, and an organic photocatalyst is unnecessary for the arylation reaction. In addition, thianthrene can also be recycled and transformed to thianthrenium salts without affecting the efficiency of these reactions. The protocol demonstrates excellent tolerance of functional groups and viable functionalization of late-stage natural products and pharmaceutically relevant molecules. [ABSTRACT FROM AUTHOR]

Selective oxidation of alcohols to aldehydes/ketones is an important reaction in the fine and bulk chemicals fields. However, the classical alcohol oxidation methods are often performed under unfriendly conditions or use stoichiometric oxidants. Herein, we report an ingenious system that enables high selectivity (up to 99%) and high conversion (up to 97%) with high reaction rates in the aerobic oxidation of alcohols to aldehydes/ketones for a broad range of alcohols, proceeding smoothly via mixing the solvent ethyl acetate and HBr under ambient conditions with visible light irradiation. Experimental characterization and theoretical calculations reveal that solvated dispersion intermediates are formed spontaneously in situ through noncovalent interactions among the molecules in the reaction system, which is proposed to be the origin of the high selectivity and high activity of this reaction. The dispersion system provides a feasible activation approach for aerobic oxidation of alcohols to aldehydes/ketones with high performance under visible light. [ABSTRACT FROM AUTHOR]

GreenChemistry Cutting- edge research for a greener sustainable future rsc. li/ greenchem Volume 26 Number 10 21 May 2024 Pages 5585- 6220 ISSN 1463- 9262 PAPER Indrajit Ghosh, Burkhard König et al. C( sp 2 )– S cross- coupling reactions with nickel, visible light, and mesoporous graphitic carbon nitride [Extracted from the article]

Cross-coupling reactions play a vital role in modern organic synthesis, enabling the construction of necessary C–C or C–(het)atom bonds for synthetic transformations. Although C(sp2)–C and C(sp2)–N cross-coupling reactions have received significant attention, recent advancements have also highlighted the significance of C(sp2)–S cross-coupling reactions. These reactions lead to the synthesis of valuable compounds, including pharmaceuticals and materials. In a recent report, we introduced Adaptive Dynamic Homogeneous Catalysis (AD-HoC) as an efficient method for C(sp2)–S cross-coupling reactions. This method operates without the need for any ligands, base, or additional additives, relying solely on essential parameters. In this report, we discuss the use of mesoporous graphitic carbon nitride (mpg-CN) as an all-organic heterogeneous photocatalyst in such transformations. The versatility and robustness of the reaction are showcased with fifty synthetic examples, achieving up to a 98% yield. The use of mpg-CN as a catalyst additionally enables the easy recovery of the photocatalyst from the reaction mixture and facilitates the sequential execution of multiple cross-coupling reactions with consistent yields of the desired products using a simple setup. This approach is a significant advancement in the field, both in terms of operational simplicity and environmental impact, traits that we all envision for sustainability. [ABSTRACT FROM AUTHOR]

Herein, we report the intermolecular photocatalytic addition of amines and alkenes using metal-free conditions. Benzophenone was added as a photosensitizer to accelerate the single electron transfers, H-atom transfers and generation of α-aminoalkyl radicals. N-Alkyl anilines were alkylated with high selectivity and broad substrate scope. [ABSTRACT FROM AUTHOR]

The drawbacks commonly observed in synthetic methods for alcohol oxidation often stem from the utilization of complex, toxic, hazardous, or waste-producing oxidants. When sensitive or complex substrates bearing several functional groups are to be transformed, the selectivity of oxidation becomes another significant challenge. Herein, a chemoselective and operationally simple catalyst-free and additive-free method is presented for the aerial oxidation of 1-phenylpropargyl and 1-phenylallyl alcohols to their corresponding ketones, requiring only a solvent and visible light irradiation. The crucial role of dimethylsulfoxide (DMSO) as the solvent lies in achieving high chemoselectivity. Singlet oxygen, whose formation is photosensitized by the substrate and the product, is captured by DMSO, thereby preventing the undesired over-oxidation that occurs in other solvents. The application of DMSO to protect the substrate against singlet oxygen represents a novel approach that is potentially applicable to other aerobic photocatalytic processes. [ABSTRACT FROM AUTHOR]

We established an efficient photocatalyzed arylsilylation of alkenes, utilizing readily accessible silylboronates and (hetero)aryl nitriles in the presence of a base. This reaction proceeds through a photoredox-triggered cascade of single-electron transfers of base/silylboronate adducts and (hetero)aryl nitriles with the photocatalyst, leading to the formation of the silyl radicals and (hetero)aryl nitrile radical anions. This is followed by sequential coupling with alkenes, yielding valuable 1,1-diaryl derivatives with a silicon group at the β-position. This protocol features good functional group tolerance, mild reaction conditions, and broad substrate scopes, and thus can be applicable to the structural modification of bioactive molecules. [ABSTRACT FROM AUTHOR]

Chemical transformation triggered by an electron donor–acceptor (EDA) complex without the addition of an exogenous stoichiometric electron donor/acceptor is rare. Herein, we report such a process to access 2,3-difunctionalized pyridines from readily available N-aminopyridiniums (1) and activated alkenes (2) promoted by visible light. This procedure offered multi-substituted pyridines in satisfactory yields at room temperature with broad functional group tolerance. The reaction can be easily performed on a gram scale without the loss of yield. The modification of bioactive molecules including derivatives of clinical drugs and natural products was demonstrated. Mechanistic studies and DFT calculations indicated that the formal [3 + 2] cycloaddition and aza-Michael addition between 1 and 2 generated tetrahydropyrazolo[1,5-a]pyridine and a new pyridinium salt, respectively. These two intermediates formed an EDA complex, which under visible-light illumination, triggered the following single electron transfer (SET)/N–N bond cleavage/C–N bond formation cascade process with high atom economy. [ABSTRACT FROM AUTHOR]

In this study, a TiO2-P25 photocatalyst was chemically complexed with a triethanolamine (TEOA) molecule using visible light irradiation and its photocatalytic activity was evaluated in the photoreduction of a wide range of nitroaromatic compounds. The chemically adsorbed TiO2-TEOA complexes were characterized by Fourier-transform infrared spectroscopy, thermogravimetric analysis, UV–vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, N2 adsorption/desorption isotherm analysis and dynamic light scattering (DLS) analysis. The TEOA-functionalized TiO2-P25 surface complex shows enhanced photocatalytic activity under visible light irradiation (λ = 400 nm) when compared to pure TiO2-P25. This enhancement results from the charge transfer (CT) complex formation between TiO2 and TEOA, as well as electron transfer via a ligand-to-metal charge transfer (LMCT) mechanism. Interestingly, in the presence of a nitro compound (NC), the chemically absorbed TiO2-TEOA forms a TiO2-TEOA-NC triad complex system. The three components spontaneously self-assemble into a heterosupramolecular system that performs electron transfer as a single function. As a result, after absorbing visible light, the triad system demonstrates unique photocatalytic performance as compared to both TiO2-TEOA and TEOA-nitro complexes. The increased charge separation in the triad system was demonstrated by photocurrent and electrochemical impedance spectroscopy (EIS) under visible light irradiation. Electrochemical techniques, including photocurrent, impedance, light absorption and emission spectroscopies, demonstrated that increasing the current and charge separation within the triad system effectively inhibits the recombination of electron-hole pairs. The results of the study indicate that the conversion of nitroarenes to their corresponding amines can take place rapidly and on a large scale, yielding excellent results even under atmospheric pressure and air. It is noteworthy that this is the first study in this area, which highlights the potential of reducing nitroarenes into their corresponding amines with a high efficiency of up to 5 mmol using a photocatalytic procedure. The chemoselectivity of this system was excellent, even in the presence of other reducible groups in the nitro compound. Additionally, a one-pot reductive conversion of nitroarenes to amides was carried out with high efficiency using triethyl orthoformate, acetic anhydride, and benzoic anhydride. [ABSTRACT FROM AUTHOR]

Donor (D)–acceptor (A) structured conjugated polymers (CPs) have attracted increased attention owing to their application in efficient photocatalytic hydrogen production from water, benefiting from their unique advantages of high charge mobility, strong light-harvesting ability, and tunable band gaps. As a typical "A" building block to construct D–A type CPs, thieno[3,4-c]pyrrole-4,6-dione (TPD) may bind co-catalyst, similar to Pt though the σ–π anchor of its carbonyl group with Pt to enhance the performance of solar-driven hydrogen production. Herein, we developed three TPD-based D–A-type CPs, namely, TPD2T, TPDTT, and TPDBDT, using 2,2′-bithiophene (2T), cyclopenta[2,1-b:3,4-b]dithiophene (TT), and benzo[1,2-b:4,5-b]dithiophene (BDT) as "D" units, via direct C–H/C–H coupling polycondensation, offering an atom-economic and eco-friendly way to achieve new CP materials for highly effective hydrogen evolution. Among them, TPDBDT-based nanoparticles exhibited the highest photocatalytic activity with remarkable hydrogen evolution rates of 1819.4 μmol h−1 g−1 and 7420.0 μmol h−1 g−1 in the absence and presence of co-catalyst Pt, respectively. The mechanism of the hydrogen production of TPD-based polymers was discussed based on DFT calculations. This work not only demonstrates the first example of CPs synthesized via C–H/C–H cross-coupling polymerization for application in water splitting for hydrogen production but also helps to understand the relationship between polymer structure and photocatalytic hydrogen production performance. [ABSTRACT FROM AUTHOR]