Gold-catalyzed stereoselective synthesis of azacyclic compounds through a redox/[2 + 2 + 1] cycloaddition cascade of nitroalkyne substrates

We report a new redox/cycloaddition cascade on readily available 1-alkynyl-2-nitrobenzenes that produces complex azacyclic compounds stereoselectively. The core structures of the resulting products are constructed through a formal [2 + 2 + 1] cycloaddition among α-carbonyl carbenoids, nitroso species, and external alkenes.     

α/γ(4)-Hybrid peptide helices: synthesis, crystal conformations and analogy with the α-helix

Synthesis, crystal conformations of α/γ(4)-hybrid peptide helices containing proteinogenic amino acid side-chains, and the analogy with the α-helix are reported. Results suggest that α/γ(4)-hybrid peptides adopted helical conformations with 12-membered H-bond pseudocycles in single crystals.     

Synthesis,spectroscopic characterization and thermal studies of some rare earth metal complexes of unsymmetrical tetradentate Schiff base ligand

The solid complexes of La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) with 4-hydroxy-3-(1-{2-(2-hydroxy-benzylidene)-aminophenylimino}-thyl)-6-methy-pyran-2-one (H₂L) derived from o-phenylenediamine, 3-acetyl-6-methyl-(2H)pyran,2,4(3H)-dione (dehydroacetic acid or DHA) and salicylic aldehyde have been synthesized and characterized by elemental analysis, conductometry, magnetic susceptibility, UV–visible, FTIR, ¹H NMR spectra, X-ray diffraction, and thermal analysis and screened for antimicrobial activity. The FTIR spectral data suggest that the ligand behaves as a dibasic tetradentate ligand with ONNO donar atoms sequence towards central metal ion. From the microanalytical data, the stoichiometry of the complexes has been found to be 1:1 (metal:ligand). The physico-chemical data suggest distorted octahedral geometry for La(III), Ce(III), Pr(III), Nd(III), Sm(III) and Gd(III) complexes. The X-ray diffraction data suggest monoclinic crystal system for La(III) and Ce(III) and orthorhombic crystal system for Pr(III) and Nd(III) complexes. Thermal behaviour (TGA/DTA) of the complexes was studied and kinetic parameters were determined by Horowitz–Metzger and Coats–Redfern methods. The ligand and their metal complexes were screened for antibacterial activity against Staphylococcus aureus, Escherichia coli and Bacillus sp. Fungicidal activity against Aspergillus niger, Trichoderma and Fusarium oxysporum.     

Synthesis of fluorescent carboxylic acid ligands for construction of monolayers on nanostructures

Two new long-chain carboxylic acids (1, 2) bearing strong fluorescent group pyrene as ligands for Self-Assembled Monolayers (SAMs) have been synthesized. The multistep targeted synthesis is accomplished by use of Pyren-1-yl methylamine hydrochloride and employing simplified synthetic protocols. Compound 2 contains a chiral center purposely introduced along the atom chain in order to make it suitable for chiro-optical studies of the resulting SAMs.      

Oligoethylene glycols as highly efficient mutifunctional promoters for nucleophilic-substitution reactions

Herein, we report the promising use of n-oligoethylene glycols (oligoEGs) as mutifunctional promoters for nucleophilic-substitution reactions employing alkali metal salts. Among the various oligoEGs tested, pentaethylene glycol (pentaEG) had the most efficient catalytic activity. In particular, when compared with other nucleophiles examined, a fluorine nucleophile generated from CsF was significantly activated by the pentaEG promoter. We also performed various facile nucleophilic-displacement reactions, such as the halogenation, acetoxylation, thioacetoxylation, nitrilation, and azidation of various substrates with potassium halides, acetate, thioacetate, cyanide, and sodium azide, respectively, in the presence of the pentaEG promoter. All of these reactions provided their desired products in excellent yields. Furthermore, the combination of pentaEG and a tert-alcohol medium showed tremendous efficiency in the nucleophilic-displacement reactions (fluorination and methoxylation) of base-sensitive substrates with basic nucleophiles (cesium fluoride and potassium methoxide, respectively). The catalytic role of oligoEGs was examined by quantum-chemical methods. The oxygen atoms in oligoEGs were found to act as Lewis bases on the metal cations to produce the "flexible" nucleophile, whereas the two terminal hydroxy (OH) groups acted as "anchors" to orientate the nucleophile and the substrate into an ideal configuration for the reaction.     

New 2-aminoethylimidazole-based dicarboxylic acid receptor derived from cholestane

A new facial amphiphile cholestane-based receptor 1 containing a 2-imidazolylethylamino moiety at the 3α and 7α positions of cholestane was synthesized. Recognition selectivity of the new receptor 1 with various dicarboxylic acids was assessed by ¹H NMR titration. Maleic acid showed the highest binding constant among all the tested acids (K_a = 9.36 × 10⁴ M⁻¹).     

Selective recognition of H2PO4- by a cholestane-imidazole-zinc ensemble

A new facile amphiphile cholestane-based zinc complex 4 containing a 3-aminopropylimidazole moiety at the 3α and 7α positions of cholestane was designed and synthesized. Recognition selectivity of the new receptor 4 with various anions was assessed by ¹H NMR titration. Dihydrogen phosphate showed the highest binding affinity among all the tested anions (K_a = 4.4 × 10⁵ M^?1).     

Preparation of silicon containing polymers—III: Synthesis and characterization of organosilicon azopolyamides

New silicon containing azopolyamides have been prepared from 4,4′-diaminoazobenzene and four structurally related organosilicon acid dichlorides. Polymerization was carried out by the technique of low temperature interfacial polycondensation using methylene chloride-water system. The polymers were yellow to brown in colour. They were characterized by visible and i.r. spectroscopy, X-ray diffraction, solubility and by solution viscosity. Thermal behaviour of these polyamides was studied by dynamic thermogravimetry.