Functionalization of Pyridine and Quinoline Scaffolds by Using Organometallic Li-, Mg- and Zn-Reagents

This Review discusses the various methods for functionalizing pyridine and quinoline scaffolds, including direct selective metalation (DoM), halogen/metal exchange reactions, Li, Mg, and Zn insertion, and trans-metalation approaches, which are then followed by cross-coupling reactions of the Kumada or Negishi types. Selective deprotonation of aryl or pyridyl/quinolinyl derivatives can be performed using n-BuLi, LDA, and TMP-based different organolithium, -magnesium, and -zinc reagents. The functionalized pyridine and quinoline-based heterocyclic compounds were prepared by selectively deprotonating with presenting a directing functional group substituted pyridine/quinoline analogues in the presence of TMP-bases (TMP−Li, Mg, Zn reagents). Different aryl or alkyl Li, Mg, and Zn reagents with electron-donating and electron-withdrawing substituents undergo transition metal-catalyzed C(sp²)−C(sp²) and C(sp²)−C(sp³) types of cross-coupling reactions with pyridine/quinoline halides under mild conditions with the sustainable process producing complex N-heterocycles. Using moderate and sustainable reaction conditions, sensitive functional group tolerance, and inexpensive and low toxic chemicals, highly functionalization of pyridine and quinoline-based bioactive therapeutic scaffolds and natural products was accomplished. Therefore, in this article, we provide a succinct overview of the numerous synthetic strategies and practical methods used by various authors between 2010 and 2023 to functionalize pyridine and quinoline analogues using diverse Li, Mg, and Zn organometallic reagents.     

Acetic Acid-Mediated Synthesis of Kojic Acid Derivatives

Russian Journal of Organic Chemistry - A green acetic acid-mediated synthesis of kojic acid derivatives through a multicomponent reaction (MCR) has been developed. This new protocol is simple and...     

Alternative proton-conducting electrolytes and their electrochemical performances

This study was focused on the performances of membrane electrode assemblies (MEAs) consisting of the proton–conducting 90PVA/3PWA/4GPTMS/1P₂O₅/2Gl and 80PVA/10PWA/6GPTMS/2P₂O₅/2Gl hybrid membranes as electrolytes together with a Pt/C electrode for proton exchange membrane fuel cells. The MEAs were fabricated and tested as a function of temperature and humidity, and yielded a current density value of about 350?mA?cm^?2 at 60?°C and 100% relative humidity (RH) for the membrane electrolyte 80PVA/10PWA/6GPTMS/2P₂O₅/2Gl. These values were compared with Nafion? membranes, and the single-cell performances based on proton-conducting organic/inorganic hybrid electrolytes were discussed. The test conditions employed were equivalent for each MEA that had an active area of 5?cm². These hybrid membranes showed a high proton conductivity in the range of 10^?3–10^?2 S cm^?1 at low temperatures, i.e., 60, 80, and 90?°C, and 50%, 75%, and 100% RH.     

A new approach to construct a fused 2-ylidene chromene ring: highly regioselective synthesis of novel chromeno quinoxalines

Regioselective construction of a fused 2-ylidene chromene ring was achieved for the first time by using AlCl(3)-induced C-C bond formation followed by Pd/C-Cu mediate coupling-cyclization strategy. A number of chromeno[4,3-b]quinoxaline derivatives were prepared by using this strategy. Single crystal X-ray diffraction study of a representative compound e.g. 6-(2,2-dimethylpropylidene)-4-methyl-6H-chromeno[4,3-b]quinoxalin-3-ol confirmed the presence of an exocyclic C-C double bond with Z-geometry. The crystal structure analysis and hydrogen bonding patterns of the same compound along with its structure elaboration via propargylation followed by Sonogashira coupling of the resulting terminal alkyne is presented. A probable mechanism for the formation of 2-ylidene chromene ring is discussed. Some of the compounds synthesized showed anticancer properties when tested in vitro.     

Reagent‐Based DOS: Developing a Diastereoselective Methodology to Access Spirocyclic‐ and Fused Heterocyclic Ring Systems

Herein, we report a diversity‐oriented‐synthesis (DOS) approach for the synthesis of biologically relevant molecular scaffolds. Our methodology enables the facile synthesis of fused N‐heterocycles, spirooxoindolones, tetrahydroquinolines, and fused N‐heterocycles. The two‐step sequence starts with a chiral‐bicyclic‐lactam‐directed enolate‐addition/substitution step. This step is followed by a ring‐closure onto the built‐in scaffold electrophile, thereby leading to stereoselective carbocycle‐ and spirocycle‐formation. We used in silico tools to calibrate our compounds with respect to chemical diversity and selected drug‐like properties. We evaluated the biological significance of our scaffolds by screening them in two cancer cell‐lines. In summary, our DOS methodology affords new, diverse scaffolds, thereby resulting in compounds that may have significance in medicinal chemistry.     

A concise enantioselective synthesis of 1,4-dideoxy-1,4-imino-d-arabinitol using Co(III)(salen)-catalyzed hydrolytic kinetic resolution of a two-stereocentered anti-azido epoxide

A concise enantioselective synthesis of 1,4-dideoxy-1,4-imino-d-arabinitol, (+)-DAB-1, has been described in good overall yield (18.1%) and with high enantiomeric purity (up to 98% ee) starting from a simple raw material, cis-2-butene-1,4-diol. The Co-catalyzed hydrolytic kinetic resolution of a two-stereocentered racemic azido epoxide followed by asymmetric dihydroxylation of the alkene and ‘one pot’ reductive cyclisation of the azido diol are key reactions in the synthetic sequence.     

57Fe Mössbauer studies in a new cluster spin glass system RuxFeGa (0.5≦x≦1.5)

⁵⁷Fe Mössbauer and bulk magnetization studies have been carried out in a new magnetic system Ru_xFeGa for 0.5x1.5. The system is seen to freeze into a cluster spin glass phase at 70 K. The freezing temperature and the hyperfine field at Fe at the lowest measured temperature, 190 kOe, is essentially same for all values of x investigated.     

Simple and efficient method for aromatization of tetrahydro-β-carbolines by using K2S2O8 as a catalyst and its antimicrobial activity comparison with molecular docking studies

Russian Journal of General Chemistry - A novel and efficient aromatization of tetrahydro-β-carbolines under mild conditions using K2S2O8 as a catalyst was developed. The method is applicable...