Current Catalysis - Volume 12, Issue 1, 2023

In recent years, photocatalytic multi-component reactions have emerged as a cuttingedge innovation in the field of organic synthesis. These reactions allow the simultaneous transformation of multiple reactants, which not only saves time and resources but also provides access to a diverse range of complex molecules. The use of photocatalysts in these reactions provides several advantages, including mild reaction conditions, high selectivity, and high functional group tolerance. Moreover, the integration of renewable energy sources such as visible light as a driving force for these reactions further adds to their sustainability. This innovation has opened up new avenues for the synthesis of complex molecules and holds great promise for the development of sustainable and efficient chemical processes. This review gives a broad understanding of photocatalyzed multi- component reaction protocols developed with wide applications in synthetic organic chemistry. These green, efficient, and straightforward reactions utilize recyclable photocatalyst, solvent-free or catalyst-free conditions for the synthesis of compounds with biological significance in a costeffective fashion. They are easily purified due to the minimum or no by-product formation. The review is divided into sections based on the type of photocatalysts involved and covers literature up to 2022.

Background: Neuraminidase enzymes are a large family found in a range of organisms. The best-known neuraminidase is viral neuraminidase, a drug target for the prevention of the spread of influenza infection. The viral neuraminidases are frequently used as antigenic determinants found on the surface of the influenza virus. Objective: Thiazolidine derivatives have been synthesized and explored previously, and further compounds have been designed on the basis of leading compounds. This research aimed to validate those previously synthesized compounds and a new series of compounds. Methods: A series of 28 compounds of thiazolidine-4-carboxylic acid derivatives were studied and evaluated for their ability to inhibit the neuraminidase (NA) of the influenza A virus. Twenty-eight compounds were differentiated into a training set of 21 compounds and a test set of 07 compounds. Results: The validated compounds demonstrated moderate inhibitory activity against influenza A neuraminidase. The most potent compound was acetaminophen mercapturate (C13H16N2O5S) (MW: 312.34). S-(5-acetamido-2-hydroxyphenyl)-N-acetyl-L-cysteine is an S-substituted N-acetyl-Lcysteine in which the S-substituent is specified as 5-acetamido-2-hydroxyphenyl. It acts as a drug metabolite, a human urinary metabolite, and a rat metabolite. It is a member of acetamides, an organic sulphide, a member of phenols and an S-substituted N-acetyl-L-cysteine. It derives from “paracetamol”. Conclusion: Validation of inhibitory activity of thiazolidine-4-carboxylic acid derivatives as novel influenza NA shows drug discovery of a more potent and reliable drug for the influenza virus.

Background: Catalytic depolymerization and processing of cellulose can be used to produce value-added renewable feedstock chemicals. Objective: This study aimed to develop an acidic ionic liquid-metal ion chloride catalyst system-based single-reactor method for processing cellulose into value-added products. Methods: The effect of metal chlorides as co-catalysts on 1-(1-propylsulfonic)-3-methylimidazolium chloride acidic ionic liquid catalyzed degradation of cellulose in 40% (v/v) aq. ethanol was studied by measuring levulinic acid, ethyl levulinate, and 5-hydroxymethylfurfural yields. Results: In experiments with Mn(II) and Zn(II) chloride co-catalysts at 160 and 170°C for 12 h, the initial yields of ethyl levulinate and 5-hydroxymethylfurfural improved from ~ 7% to ~ 12-15% due to co-catalytic effects. The highest enhancements in ethyl levulinate yields were observed with CrCl3, where the yield increased from 6 to 27% with the addition of a 10 mol% co-catalyst. Conclusion: All three transition metal chlorides studied caused improvements in yields of secondary products, ethyl levulinate and 5-hydroxymethylfurfural, in acidic ionic liquid catalyzed degradation of cellulose in aqueous ethanol. The most significant enhancements in ethyl levulinate yields were observed with CrCl3 as a co-catalyst.

The ammonium-tethered pyrrolidine-based organocatalyst catalyzed asymmetric Michael addition/cyclization reaction of α,β-unsaturated aldehydes with 3-hydroxyoxindole in aqueous media was developed, giving the spirooxidole lactones in high yields with high enantioselectivities. Background: The asymmetric Michael addition/cyclization reaction of 3-hydroxyoxindoles with α,β- unsaturated aldehydes is an important method for the synthesis of chiral spirooxindole derivatives, which are found in a wide range of biologically active natural products and pharmaceutical agents. Objective: Organocatalyzed asymmetric Michael addition/cyclization reactions are one of the most powerful and effective approaches for the construction of complex molecules from relatively simple starting materials. However, a major problem associated with these organocatalytic system is that high catalyst loading and organic solvents are required. In the present work, our objective was to develop a water-compatible organocatalyst that aimed at lowering catalyst loading and being active in an aqueous system. Methods: In a typical experiment, To a solution of catalyst 2a (0.008 mmol) and PhCO2H (0.096 mmol) in 0.5 mL of a mixture solvent iPrOH/H2O (1:3) was added α,β-unsaturated aldehyde (0.4 mmol) and 3-hydroxyoxindole (0.8 mmol). The reaction mixture was proceeded at room temperature for 16 hours, and then was extracted with 10 mL dichloromethane to give the cyclized hemiacetal, which was subjected to the direct oxidation with pyridinium chlorochromate (PCC, 1.2 mmol) for 16 hours to give the desired spirooxindole lactones. Results: The reactions successfully gave spirooxindole lactones in high to excellent yields (81-95%) with moderate to excellent enantioselectivities (up to 99% ee). However, the diastereoselectivities were poor ranging from 1:1.1 to 1:2.3. Conclusion: The asymmetric Michael addition/cyclization reaction of α,β-unsaturated aldehydes with 3-hydroxyoxindole using ammonium-tethered pyrrolidine-based organocatalyst has been developed. The reaction was performed in aqueous media with low catalyst loading (2 mol%) and provided the spirooxidole lactones in high yields (81-95%) with high enantioselectivities (ee: up to 99%).

Background: An abatement of emission of particulate matter (mainly soot) is a challenge for the scientific community. An active and cheap catalytic system for soot combustion can help solve this problem. Objective: The aim of this study was to investigate the influence of the composition of a series of Mn3-xFexO4 (x = 0 - 3) oxides of spinel structure on their catalytic properties in soot combustion. Methods: Samples were synthesized by coprecipitation followed by a consecutive thermal treatment. Their structure was verified by X-ray diffraction and Raman spectroscopy. The obtained catalysts were tested in model soot oxidation (Printex U) in both tight and loose contact modes. Results: It was found that different mechanisms of soot combustion occurred dependently on a chosen contact mode. Conclusion: It was confirmed that in the case of tight contact (TC), a coexistence of divalent manganese and iron species was decisive for the catalytic activity, whereas a presence of trivalent manganese centers was crucial in the case of loose contact (LC). Mn1.2Fe1.8O4 was found to be the most active catalyst.