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Aromatic Helicenes
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2020
Importantly, various synthetic methodologies were published to transform nonracemic biaryl precursors into nonracemic helicenes, thus demonstrating an excellent relay of stereochemical information when transforming axial chirality into helicity. An efficient synthetic route to highly enantioenriched 1-aza[6]helicenes 28 was developed by Fuchter et al. who succeeded in converting the separated atropisomers of the axially chiral biaryl (separated by semipreparative HPLC on a chiral column) through alkyne–arene cycloisomerization into azahelicene products (Weimar et al., 2013). Srebro-Hooper, Crassous, Guy et al. built an enantiopure backbone of the diazahelicene-like dibenzo[c]acridine derivative from the optically pure axially chiral bis-tetralone, which was obtained from racemate by preferential crystallization (it formed conglomerate) (Bensalah-Ledoux et al., 2016). Kamikawa et al. converted an enantiopure biaryl building block (obtained by resolution of the corresponding racemate by liquid chromatography on a chiral column) into enantiopure 6-aza[6]helicene in good yield by utilizing a palladium-catalyzed C-H annulation reaction (Kaneko et al., 2013). Nozaki et al. reported an efficient strategy for the synthesis of highly enantioenriched aza- and oxa[7]helicenes from the nonracemic biaryl precursor (4,4′-biphenanthryl-3,3′-diol) in good yields (Nakano et al., 2005).
Imidazolium Hydroxides and Catalysis
Published in Pedro Lozano, Sustainable Catalysis in Ionic Liquids, 2018
Base catalysis is important for a wide range of organic transformations. These include, but are certainly not limited to, aldol reactions and condensations; Michael additions; Henry reactions, Dieckmann, Knoevenagel and Claisen−Schmidt condensations; and the Robinson annulation. Given the synthetic importance of base-catalyzed reactions and the use of ionic liquids (ILs) as “designer solvents,” an approach to conducting base catalyzed processes has been to utilize ILs that possess a basic anion. This methodology has the advantage of simplifying the reaction medium and the subsequent purification, as the IL acts as both the solvent and as a catalyst for the reaction, reducing the need for other additives. Alternatively, this methodology can be used to enable the base to become miscible with various organic solvents and therefore provide inorganic type bases with organic solvent solubility. As one of the most studied classes of these ILs, the focus of this chapter will be on imidazolium hydroxides and their role in various catalytic transformations. The abbreviations used for the imidazolium salts will be based on the alphanumeric system used by Hallett and Welton, for example, the 1-butyl-2-methyl-3-ethylimidazolium cation would be [C4C2C12im].1
Synthesis of Ionic Liquid Mediated Nanoparticle Synthesis
Published in Nandakumar Kalarikkal, Sabu Thomas, Obey Koshy, Nanomaterials, 2018
Praveenkumar Upadhyay, Vivek Srivastava
ILs show great potential for chemical analysis as a solvent. In recent advancements, the ILs have shown various analytical applications in chromatography, extraction, electrochemistry, and sensor technology.34 There are various applications of ILs as a solvent, catalyst, and as support for several important organic reactions like hydrogenation, hydroformylation, alkoxycarbonylation, cross coupling like Heck, Suzuki, Negishi, Stille reactions, allylic substitution, Friedel-Crafts alkylation, Diels-Alder, Diol or carbonyl protection, Epoxidation/epoxide opening, cyanosilyation of aldehydes, esterification, ring closing metathesis, Knoevenagel condensation, Baylis-Hillman, Robinson annulation, alcohol oxidation Friedlander reaction, nitration of phenols, bromination of alkynes, biocatalysis, and chiral solvent for asymmetric synthesis (Table 4.2). ILs have also been utilized as storage medium for toxic gases, lubricant additives in pigments, and as propellants.
A combined experimental and TDDFT-DFT investigation of structural and optical properties of novel pyrazole-1, 2, 3-triazole hybrids as optoelectronic devices
Published in Phase Transitions, 2021
I. H. El Azab, A. Ibrahim, M. Abdel El-Moneim, M. Sh. Zoromba, M. H. Abdel-Aziz, M. Bassyouni, A. F. Al-Hossainy
During the last two decades, several efforts have been oriented for converting solar energy into electricity, using dye-sensitized solar cells (DSSCs) owing to their high conversion potency and their potential low cost [1]. To advance the act of DSSCs, a great effort of research is being achieved on semiconductor nanocrystalline titanium oxide (TiO2) electrodes, [2,3] molecular dyes [4], electrolytes [5], and counter electrodes [6,7]. Organic moieties play a crucial role in photovoltaic and light collecting systems due to their admirable optical and electrical properties [8]. Recently organic fragments in practically, 1,2,3-triazoles have been used as additives in the electrolytic solution of DSSC [9,10]. Click reaction refers to Cu(I)-catalyzed cycloaddition of azide to alkyne to furnish 1,2,3-triazole using slight reaction conditions in a good yield. The 1,2,3-Triazole skeleton has an extensive range of applications in industrial, biological, and therapeutic fields [11,12]. Moreover, 1,2,3-triazole moiety acts as a powerful E-acceptor component, usually utilized to modulate the HOMO or LUMO energy levels for low bandgap features in optoelectronic and photophysical devices [13–16]. Based on the above-mentioned applications of 1,2,3-triazole unit, and to continue our efforts at annulation a new N-containing heterocycle [17–27], we report herein an efficient synthetic tactic for the preparation of 1,2,3-triazole-based frames, using azide–alkyne Huisgen cycloaddition reaction, to study its optical properties.