Role of non-conventional hydrogen bonding in controlling regioselectivity for nucleophilic aromatic substitution of 4,6-dinitroisoindoline-1,3-dione with 1,2,3-triazole isomers: a computational studies

Structural Chemistry - The nucleophilic aromatic substitution reactions of 4,6-dinitroisoindoline-1,3-dione with 1,2,3-triazole isomers, i.e., 1H-1,2,3-triazole and 2H-1,2,3-triazole, have been...     

Ultrasound‐Assisted Facile Synthesis and Antimicrobial Studies of Alkanediyl‐bis‐thiazolidin‐4‐ones and Alkanediyl‐bis‐thiazinan‐4‐ones

Alkanediyl‐bis‐2‐aryl‐thiazolidin‐4‐one and alkanediyl‐bis‐2‐aryl‐1,3‐thiazinan‐4‐one derivatives have been congregated in a single step reaction of diaminoalkanes, aryl aldehydes, and sulfanyl acids in the presence of coupling agent N,N′‐dicyclohexylcarbodiimide under ultrasonic conditions. This method of constructing 4‐keto derivatives of thiazolidine and thiazinane is quick and clean besides yielding the products in quantitative yields. The spectral techniques corroborated the structures of the isolated products. Biological assay of the synthesized products has also been reported.     

A study on the BF3 directed lithiation of 3-chloro- and 3-bromopyridine

The BF₃-directed lithiation of 3-chloro- and 3-bromopyridine (1a and 1b, respectively) has been investigated. The reactions of 3-chloro- or 3-bromopyridine–BF₃ adduct with LDA (1.3/1.1 equiv) followed by quenching with benzaldehyde or iodine exclusively gave the C-2 substituted products. However, when 2.2 equiv of LDA and dimethyl disulfide was used, a C-6 substituted product was obtained. Dilithiation of 1a and 1b has been studied with and without the involvement of BF₃ complexation. The role of Li?F(BF₃) interactions has been investigated by experimental and DFT calculations.     

A Study on the Antioxidant Activity of Pyridylselenium Compounds and their Slow Release from Poly(acrylamide) Hydrogels

Abstract

The antioxidant activity of pyridylselenium compounds has been evaluated by 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and nitric oxide (NO) scavenging methods. Pyridylselenium compounds have shown far superior (100–1000 times) antioxidant property than ebselen. The control release of bis(2-pyridyl) diselenide from poly(acrylamide) hydrogels has been studied in order to evaluate its release mechanism and diffusion coefficient. The later study also demonstrates that the pyridylselenium loading into the polymer matrix increases the magnitude and the rate of the radical scavenging activity of the poly(acrylamide) hydrogels.     

Synthesis and characterization of 3,5-lutidinyl chalcogen and -dichalcogen compounds: X-ray crystal structure of bis(3,5-dimethyl-2-pyridyl) diselenide and 2,6-bis(selenomethyl)-3,5-lutidine

The synthesis of 3,5-lutidinyl chalcogen and -dichalcogen compounds has been described by a method involving selective mono- and dilithiation of 3,5-lutidine (1) ring. The selective mono- and dilithiation of 1 has been achieved by reacting BF₃-complexed 3,5-lutidine (2) with 1 and 2 equiv of LTMP/LDA respectively. The subsequent insertion of elemental selenium followed by aerial oxidation or quenching with iodomethane leads to the formation of bis(3,5-dimethyl-2-pyridyl) diselenide (5) and 2,6-bis(selenomethyl)-3,5-lutidine (7) respectively. In addition, sequential incorporation of sulfur and selenium atom in the same lutidine ring has been reported for the first time. Single-crystal X-ray studies of (5), having a rare C-Se-Se-C torsion angle of 180°(4), and (7) have also been reported.     

Synthesis and characterization of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide: X-ray structure of 4-methoxy-3-(sulfanylmethyl)- and 4-chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-carboxamide

Synthesis of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide (1a and 1b respectively) has been reported. 1a and 1b were lithiated with 2 equiv. of n-BuLi or LDA at ?78 °C. Addition of elemental sulfur or selenium to the carbanion led to the formation of corresponding thiolate or selenolate anions respectively. The selenolate anions were aerial oxidized to afford the corresponding diselenides. The thiolate/selenolate anions were quenched with a variety of electrophiles to give unsymmetrical thio/selenoalkanes in moderate to good yields. Reductive cleavage of Se–Se bond has also been studied. The synthesized compounds were characterized by elemental analysis, NMR (¹H, ¹³C and ⁷⁷Se), FT-IR and mass spectral techniques. Crystal structures of two compounds, 6b and 7a, were determined by single crystal X-ray crystallography. Their crystal structure exhibits 1,4-type S?OCH₃ and Se?Cl intramolecular secondary interactions respectively. The relative thermal stability of 3a, 3b and 4a has also been established by thermogravimetric analysis.     

Theoretical study of DABCO-based ionic liquid: synthesis and reaction mechanism

Quaternary ammonium salt obtained from the Menshutkin reaction between DABCO and benzyl chloride has been used in the synthesis of a novel Bronsted acidic ionic liquid (IL), namely 1-benzyl-4-(sulfobutyl)-diaza-bicyclo-octane hydrogen sulfate. The reaction of DABCO with benzyl chloride is a crucial step in the synthesis of this IL. Density functional theory calculations at B3LYP/6-31G(d,p) level have been employed to investigate the mechanism of Menshutkin reaction by calculating the energy barriers through possible transition states i.e., five-membered ring transition state and S_N2 transition state in gas phase and in diethyl ether as a solvent. It was found that while DABCO reacts with benzyl chloride through the well-known S_N2 transition state mechanism, the corresponding reaction with chlorodiphenylmethane can proceed through both S_N2 and five-membered ring transition state mechanism. However, S_N2 transition state mechanism is still the strongly preferred one out of the two possible mechanisms. The electronic structure analysis shows that solvent effects and enhanced resonance stabilization may play a decisive role in guiding the reaction pathway.