Photocatalytic C-H Azolation of Arenes Using Heterogeneous Carbon Nitride in Batch and Flow

Graphitic Carbon Nitride as a Photocatalyst for Decarboxylative C(sp2)-C(sp3) Couplings via Nickel Catalysis

The development of robust and reliable methods for the construction of C(sp2)-C(sp3) bonds is vital for accessing an increased array of structurally diverse scaffolds in drug discovery and development campaigns. While significant advances towards this goal have been achieved using metallaphotoredox chemistry, many of these methods utilise photocatalysts based on precious-metals due to their efficient redox processes and tuneable properties. However, due to the cost, scarcity, and toxicity of these metals, the search for suitable replacements should be a priority. Here, we show the use of commercially available heterogeneous semiconductor graphitic carbon nitride (gCN) as a photocatalyst, combined with nickel catalysis, for the cross-coupling between aryl halide and carboxylic acid coupling partners. gCN has been shown to engage in single-electron-transfer (SET) and energy-transfer (EnT) processes for the formation of C-X bonds, and in this manuscript we overcome previous limitations to furnish C-C over C-O bonds using carboxylic acids. A broad scope of both aryl halides and carboxylic acids is presented, and recycling of the photocatalyst demonstrated. The mechanism of the reaction is also investigated.

Heterogeneous Organocatalysts for Light-Driven Reactions in Continuous Flow

Within the realm of organic synthesis, photocatalysis has blossomed since the beginning of the last decade. A plethora of classical reactivities, such as selective oxidation of alcohol and amines, redox radical formation of reactive species in situ, and indirect activation of an organic substrate for cycloaddition by EnT, have been revised in a milder and more sustainable fashion via photocatalysis. However, even though the spark of creativity leads scientists to explore new reactions and reactivities, the urgency of replacing the toxic and critical metals that are involved as catalysts has encouraged chemists to find alternatives in the branch of science called organocatalysis. Unfortunately, replacing metal catalysts with organic analogues can be too expensive sometimes; however, this drawback can be solved by the reutilization of the catalyst if it is heterogeneous. The aim of this review is to present the recent works in the field of heterogeneous photocatalysis, applied to organic synthesis, enabled by continuous flow. In detail, among the heterogeneous catalysts, g-CN, polymeric photoactive materials, and supported molecular catalysts have been discussed within their specific sections, rather than focusing on the types of reactions.

Green synthesis of solketal from glycerol using metal-modified ZSM-5 zeolite catalysts: process optimization

This study investigates the production of solketal (2,2-dimethyl-1,3-dioxolane-4-methanol) from glycerol via ketalization reaction using M-ZSM-5 catalysts (M = Fe, Co, Ni, Cu, and Zn). The wet impregnation method ensured precise metal loading and versatility in catalyst preparation. We present a novel approach by employing a suite of characterization techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), Thermogravimetric analysis (TGA), and Field-emission scanning electron microscopy (FE-SEM), to elucidate the catalyst's structure, bonding, surface area, thermal stability, and morphology, ultimately linking these properties to their performance. Solketal synthesis was optimized in a reactor, with parameters like temperature, glycerol:acetone molar ratio, catalyst amount, reaction time, and stirring speed. Optimal conditions were identified as 60 °C, 1:4, 0.2 g, 60 min, and 1200 rpm, respectively. Gas chromatography-mass spectrometry (GC-MS) analysis confirmed successful solketal formation. Among M-ZSM-5 catalysts tested, Cu-ZSM-5 emerged the most efficient, achieving an impressive 99% glycerol conversion and 96% solketal selectivity. Notably, Cu-ZSM-5 catalyst displayed exceptional reusability, regaining its initial activity through calcination, thus minimizing waste generation. This research unveils Cu-ZSM-5 as a highly efficient catalyst and promotes sustainability by utilizing a renewable glycerol feedstock to produce valuable solketal with applications in fuel additives, solvents, and pharmaceuticals. This work paves the way for developing environmentally friendly processes for waste valorization and producing valuable bio-based chemicals.

A fruitful century for the scalable synthesis and reactions of biphenyl derivatives: applications and biological aspects

This review provides recent developments in the current status and latest synthetic methodologies of biphenyl derivatives. Furthermore, this review investigates detailed discussions of several metalated chemical reactions related to biphenyl scaffolds such as Wurtz-Fittig, Ullmann, Bennett-Turner, Negishi, Kumada, Stille, Suzuki-Miyaura, Friedel-Crafts, cyanation, amination, and various electrophilic substitution reactions supported by their mechanistic pathways. Furthermore, the preconditions required for the existence of axial chirality in biaryl compounds are discussed. Furthermore, atropisomerism as a type of axial chirality in biphenyl molecules is discussed. Additionally, this review covers a wide range of biological and medicinal applications of the synthesized compounds involving patented approaches in the last decade corresponding to investigating the crucial role of the biphenyl structures in APIs.

Nanostructured Carbon Nitride for Continuous-Flow Trifluoromethylation of (Hetero)arenes

Efficient catalytic methods for the trifluoromethylation of (hetero)arenes are of particular importance in organic and pharmaceutical manufacturing. However, many existing protocols rely on toxic reagents and expensive or sterically hindered homogeneous catalysts. One promising alternative to conduct this transformation involves the use of carbon nitride, a non-toxic photocatalyst prepared from inexpensive precursors. Nonetheless, there is still little understanding regarding the interplay between physicochemical features of this photocatalyst and the corresponding effects on the reaction rate. In this work, we elucidate the role of carbon nitride nanostructuring on the catalytic performance, understanding the effect of surface area and band gap tuning via metal insertion. Our findings provide new insights into the structure-function relationships of the catalyst, which we exploit to design a continuous-flow process that maximizes catalyst-light interaction, facilitates catalyst reusability, and enables intensified reaction scale-up. This is particularly significant given that photocatalyzed batch protocols often face challenges during industrial exploitation. Finally, we extrapolate the rapid and simplified continuous-flow method to the synthesis of a variety of functionalized heteroaromatics, which have numerous applications in the pharmaceutical and fine chemical industries.

Heterogeneous metallaphotoredox catalysis in a continuous-flow packed-bed reactor

Metallaphotoredox catalysis is a powerful and versatile synthetic platform that enables cross-couplings under mild conditions without the need for noble metals. Its growing adoption in drug discovery has translated into an increased interest in sustainable and scalable reaction conditions. Here, we report a continuous-flow approach to metallaphotoredox catalysis using a heterogeneous catalyst that combines the function of a photo- and a nickel catalyst in a single material. The catalyst is embedded in a packed-bed reactor to combine reaction and (catalyst) separation in one step. The use of a packed bed simplifies the translation of optimized batch reaction conditions to continuous flow, as the only components present in the reaction mixture are the substrate and a base. The metallaphotoredox cross-coupling of sulfinates with aryl halides was used as a model system. The catalyst was shown to be stable, with a very low decrease of the yield (≈1% per day) during a continuous experiment over seven days, and to be effective for C–O arylations when carboxylic acids are used as nucleophile instead of sulfinates.

Recent advances in visible-light mediated functionalization of olefins and alkynes using copper catalysts

Over the past decade, visible-light photoredox catalysis has blossomed as a powerful strategy and offers a discrete activation mode complementary to thermal controlled reactions. Visible-light-mediated photoredox catalysis also offers exciting...