Letters in Organic Chemistry - Volume 22, Issue 8, 2025

In this study, the synthesis of (2S,6R,10R) and (2R,6R,10R) diastereomers of pristanic acid is described. The key step in this synthesis is the dehomologation of (3RS,7R,11R)-dihydrophytol to one-carbon shorter (2RS,6R,10R)-pristanic acid using o-iodoxybenzoic acid. The diastereomeric mixture of pristanic acid is easily separated by silica gel column chromatography after conversion to the corresponding amides, which can be converted back to (2R,6R,10R)- and (2S,6R,10R)-pristanic acids in good yields.

Over the past decades, 2,2’-bipyridines and their derivatives have significantly contributed to the field of advanced materials, synthesis, and catalysis. In particular, the structural ability of bipyridines to accommodate numerous types of functional groups with varying electronic and steric properties resulted in their diverse applications. In this regard, developing novel and cost-effective preparative methodologies for 2,2’-bipyridines having various substituents has always been a popular area of research. Starting from pyridine derivatives, the simplest route to these molecules includes homo-, hetero-, and cross-coupling reactions. This review concentrated on transition metal-mediated one-step procedures for 2,2’-bipyridines from inexpensive and abundant starting materials, specifically, pyridines and 2-halopyridines. Although this report focuses on self-coupling techniques, convenient hetero-coupling methods are included. Special attention is given to the substrate scope details of the existing methodologies.

The Mannich reaction, named after Carl Mannich, is a flexible technique for generating β-amino carbonyl compounds and is a cornerstone of organic synthesis. It produces carbon-carbon and carbon-nitrogen bonds in one step and is crucial for synthetic chemistry due to its substrate versatility. Currently, efforts are focused on green chemical modifications for sustainability. Drug design and development use this Mannich process to synthesize physiologically active chemicals, identify medications, and derivatize natural products. The Mannich reaction's role in current synthetic methodologies and its compliance with sustainable chemical practices will be highlighted in this study. The review article attempted to discuss the mechanism of the Mannich reaction, significant pharmaceutical applications and analysis in the light of the green chemistry principle. This encompasses a comprehensive review of the step-by-step process for the course of the reaction and leading pharmaceutical synthesis, together with practices that make the reaction more sustainable, underlying its overall versatility and importance in modern-day organic synthesis.

3-(N-morpholino)propanesulfonic acid (MOPS), used as an organocatalyst supported on acidic alumina (Al2O3), has been effectively employed for the synthesis of substituted quinolines through the Friedlander reaction under microwave irradiation. The process involves the cyclocondensation of 2-aminoaryl ketones with carbonyl-functionalized active methylene groups. The catalytic efficacy of the MOPS/Al2O3 system proves compatible with this cyclocondensation reaction, offering several advantages including rapid activation of reactants, maintenance of a near-neutral pH, cost-effectiveness, and high yield.

The present study's exploration of innovative techniques for the production of heterocyclic scaffolds was prompted by the significance of [1]benzopyran motifs in bioactive chemicals. Given the appealing aspects of creating innovative methodological techniques while working with heterogeneous nanocatalysts, we desired to use this method to synthesize a number of dihydro[1]benzopyrano[h][1]benzopyrans. This work set out to demonstrate the prepared Fe3O4@TiO2 nanocomposite's catalytic efficacy as a magnetically separable catalyst in the production of dihydro[1]benzopyrano[h][1]benzopyrans. 3,9-diamino-1,7-diaryl-1,7-dihydro[1]benzopyrano[8,7-h][1]benzopyran-2,8-dicarbonitriles were obtained in an easy-to-manage manner by utilizing a Fe3O4@TiO2 nanocomposite as an effective catalyst in an aqueous medium at 70°C. The in vitro antimicrobial activities of some synthesized compounds were tested by the disk diffusion method. A number of target molecules, dihydro[1]benzopyrano[h][1]benzopyrans, were successfully synthesized in high yields. The results of the antimicrobial experiment showed encouraging antibacterial effects. This study offered significant advantages of high yield and practical methodology for the synthesis of dihydro[1]benzopyrano[h][1]benzopyrans. The utilization of aqueous ethanol as an environmentally friendly medium and the Fe3O4@TiO2 nanocomposite as a magnetically separable catalyst are examples of how this work adhered to the principles of green chemistry. The biological effectiveness of some of the produced compounds was tested against both Gram-negative and Gram-positive bacteria.

The ureido moiety stands as one of the most regarded scaffolds in medicinal and organic synthesis. In this study, we endeavored to synthesize a product containing tertiary amine moieties through the nucleophilic substitution reaction of the 2-chloroethyl urea derivative with a secondary amine, utilizing either inorganic bases, such as K2CO3 or organic bases like triethylamine as acid-binding agents in diverse reaction media. Unfortunately, the reaction failed to yield the desired nucleophilic substitution product in high yield, attributed to the reactivity of the 2-chloroethyl urea derivative. The structures of potential impurities were elucidated based on comprehensive spectroscopic data, including ¹H NMR, ¹³C NMR, HRMS, HMBC, and HSQC.

Cerium oxide nanoparticles have demonstrated their effectiveness as recyclable and efficient catalysts in synthesising 2,4,5 trisubstituted imidazole derivatives. Several approaches, such as IR, ¹H-NMR, ¹³C-NMR, and mass spectrometry techniques, characterize the structures of the obtained compounds. This synthetic method incorporates several merits, including easy operational conditions, moderate time requirements, cost-effectiveness, absence of by-products, and high yield. In this study, the optimal yield was achieved with a cerium oxide concentration of 10 mol% in an ethanol medium maintained at a temperature of 80 °C for 120 to 180 minutes. To describe the molecular geometry, global reactive descriptors, MEP, and computational analyses were carried out by the DFT method with a basis set of B3LYP/ 6–31 G (d, p). It was observed that compound 4c was found to possess a larger energy gap due to a low degree of electronic conjugation compared to the other synthesised compounds. Based on the results obtained from the study of NLO properties, it was evident that compound 4d manifested first-order hyperpolarizability 11 times more significant than the standard urea. NBO analysis confirmed that in all compounds, greater stability was achieved due to intramolecular charge transfer.

A novel class of eighteen 2-((9H-carbazol-9-yl)methyl)-5-(benzylthio)-1,3,4-oxadiazole derivatives were designed, synthesized and screened for their in vitro antibacterial activities against Pseudomonas syringae pv. Actinidiae (Psa), Xanthomonas oryzae pv. Oryzae (Xoo) and Xanthomonas axonopodis pv. Citri (Xac). Preliminary bioactivity test results indicated that some compounds showed moderate to good inhibitory effects against the tested bacteria at the concentrations of 100 μg/mL and 50 μg/mL. Among them, compounds 2-((9H-carbazol-9-yl)methyl)-5-((2,6-dichloro benzyl)thio)-1,3,4-oxadiazole (5e) and 2-((9H-carbazol-9-yl)methyl)-5-((4-(trifluoromethyl)benzyl)thio)-1,3,4-oxadiazole (5m) exhibited the best inhibitory effects against Psa, Xoo and Xac than other compounds, which displayed a wide range of antibacterial activities. Further bioactive applications of these molecules are in progress in our laboratories.

A palladium-catalyzed Heck cyclization/reductive aminocarbonylation was developed for alkene-tethered carbamoyl chlorides with nitroarenes using Mo(CO)6 as a convenient CO surrogate and reductant. This process constructed one C–N bond and two C–C bonds, yielding a variety of amidated oxindoles/γ-lactams with an all-carbon quaternary stereocenter under gas-free conditions. The transformation exhibited a wide range of substrate compatibility and exceptional functional group tolerance.