Dehydrogenative Transformations of Imines Using a Heterogeneous Photocatalyst

Isocyanide-Based Multicomponent Reactions Promoted by Visible Light Photoredox Catalysis

Isocyanide-based multicomponent reactions claim a one century-old history of flourishing developments. On the other hand, the enormous impact of recent progresses in visible light photocatalysis has boosted the identification of new straightforward and green approaches to both new and known chemical entities. In this context, the application of visible light photocatalytic conditions to multicomponent processes has been promoting key stimulating advancements. Spanning from radical-polar crossover pathways, to photoinduced and self-catalyzed transformations, to reactions involving the generation of imidoyl radical species, the present literature analysis would provide a general and critical overview about the potentialities and challenges of exploiting isocyanides in visible light photocatalytic multicomponent reactions.

Local anesthetics via multicomponent reactions

Local anesthetics occupy a prime position in clinical medicine as they temporarily relieve the pain by blocking the voltage-gated sodium channels. However, limited structural diversity, problems with the efficiency of syntheses and increasing toxicity, mean that alternative scaffolds with improved chemical syntheses are urgently needed. Here, we demonstrate an MCR-based approach both towards the synthesis of commercial local anesthetics and towards novel derivatives as potential anesthesia candidates via scaffold hopping. The reactions are efficient and scalable and several single-crystal structures have been obtained. In addition, our methodology has been applied to the synthesis of the antianginal drug ranolazine, via an Ugi three-component reaction. Representative derivatives from our libraries were evaluated as neuronal activity inhibitors using local field potential recordings (LFPs) in mouse hippocampal brain slices and showed very promising results. This study highlights new opportunities in drug discovery targeting local anesthetics.

Synthetic Approaches for C-N Bonds by TiO2 Photocatalysis

Nitrogen-containing organic compounds possess the most important status in drug molecules and agricultural chemicals. More than 80% currently used drugs have at least a C-N bond. The green and mild methodology to prepare diverse C-N bonds to replace traditional harsh preparation protocols is always a hotspot in modern synthetic chemistry. TiO₂-based nanomaterials, considered as environmentally benign, stable, and powerful photocatalysts, have recently been applied in some certain challenging organic synthesis including construction of useful C-N compounds under mild conditions that are impossible to complete by conventional catalysis. This mini review would present state-of-the-art paragon examples of TiO₂ photocatalyzed C-N bond formations. The discussion would be divided into two main sections: (1) N-alkylation of amines and (2) C-N formation in heterocycle synthesis. Especially, the mechanism of TiO₂ photocatalytic C-N bond formation through activating alcohol into C=O by photo-induced hole followed by C=NH-R formation and finally hydrogenating C=NH-R into C-N bonds by combination of photo-induced electron/H⁺ assisted with loaded-Pt would be covered in detail. We believe that the mini-review will bring new insights into TiO₂ photocatalysis applied to construct challenging organic compounds through enabling photo-induced hole and electron in a concerted way on coupling two substrate molecules together with respect to their conventionally independent catalysis behavior.

α-Amino Acids as Synthons in the Ugi-5-Centers-4-Components Reaction: Chemistry and Applications

Since the first reports, the Ugi four-component reaction (U-4CR) has been recognized as a keystone transformation enabling the synthesis of peptide mimetics in a single step and with high atom economy. In recent decades, the U-4CR has been a source of inspiration for many chemists fascinated by the possibility of identifying new efficient organic reactions by simply changing one of the components or by coupling in tandem the multicomponent process with a huge variety of organic transformations. Herein we review the synthetic potentialities, the boundaries, and the applications of the U-4CR involving α-amino acids, where the presence of two functional groups—the amino and the carboxylic acids—allowed a 5-center 4-component Ugi-like reaction, a powerful tool to gain access to drug-like multi-functionalized scaffolds.

Recent advances in modified TiO2 for photo-induced organic synthesis

The recent advancements of modified TiO₂ materials as photocatalysts for organic synthesis are summarized.

TiO2 Photocatalyzed C–H Bond Transformation for C–C Coupling Reactions

Fulfilling the direct inert C–H bond functionalization of raw materials that are earth-abundant and commercially available for the synthesis of diverse targeted organic compounds is very desirable and its implementation would mean a great reduction of the synthetic steps required for substrate prefunctionalization such as halogenation, borylation, and metalation. Successful C–H bond functionalization mainly resorts to homogeneous transition-metal catalysis, albeit sometimes suffering from poor catalyst reusability, nontrivial separation, and severe biotoxicity. TiO2 photocatalysis displays multifaceted advantages, such as strong oxidizing ability, high chemical stability and photostability, excellent reusability, and low biotoxicity. The chemical reactions started and delivered by TiO2 photocatalysts are well known to be widely used in photocatalytic water-splitting, organic pollutant degradation, and dye-sensitized solar cells. Recently, TiO2 photocatalysis has been demonstrated to possess the unanticipated ability to trigger the transformation of inert C–H bonds for C–C, C–N, C–O, and C–X bond formation under ultraviolet light, sunlight, and even visible-light irradiation at room temperature. A few important organic products, traditionally synthesized in harsh reaction conditions and with specially functionalized group substrates, are continuously reported to be realized by TiO2 photocatalysis with simple starting materials under very mild conditions. This prominent advantage—the capability of utilizing cheap and readily available compounds for highly selective synthesis without prefunctionalized reactants such as organic halides, boronates, silanes, etc.—is attributed to the overwhelmingly powerful photo-induced hole reactivity of TiO2 photocatalysis, which does not require an elevated reaction temperature as in conventional transition-metal catalysis. Such a reaction mechanism, under typically mild conditions, is apparently different from traditional transition-metal catalysis and beyond our insights into the driving forces that transform the C–H bond for C–C bond coupling reactions. This review gives a summary of the recent progress of TiO2 photocatalytic C–H bond activation for C–C coupling reactions and discusses some model examples, especially under visible-light irradiation.

CuWO4 as a photocatalyst for room temperature aerobic benzylamine oxidation

We report the first example of a controlled photo-oxidation reaction on CuWO₄, the aerobic oxidative coupling of benzylamine.