Current Organic Chemistry - Volume 21, Issue 19, 2017

Objective: The short review summarizes old and more recent findings highlighting special features of polymerizations of heterocyclic monomers, which usually are not observed in processes leading to low molar mass products. These features include: Influence of the initial monomer concentration on its equilibrium concentration, role of monomer in determination of the relative reactivity of “free” ions and ion-pairs in propagation, formation of products composed of linear and cyclic macromolecules, and influence of stereospecificity of each propagation step on microstructure of the final polymer. Discussion: In polymerization of heterocyclic monomers elementary reactions responsible for synthesis of polymers are, in principle, the same as those in “classical” chemistry of heterocyclic small molecules. However, these two classes of processes are distinct, because in the majority of polymerization systems the same heteroorganic groups are present in substrates (monomers) and reaction products (linear polymers). Results: In result, the active polymerization centers react not only with monomers but also with polymers. Moreover, in polymerization processes the monomer always constitutes a significant part of the liquid medium and influences its physicochemical properties.

Background: 4-Hydroxyquinolin-2-ones and quinoline-2,4-diones, a subset of the quinolone scaffold, have attracted attention due to their biological properties. These structures are present in many classes of natural products and pharmaceutical agents and show promise in antiviral and antibacterial treatment. They possess anticonvulsive effects, selective affinity to cannabinoid receptors, and other interesting biological activity. Some of these compounds have the potential for protection and properties modification of natural as well as synthetic materials as antioxidants, antidegradants, antifungal agents, UV absorbers, optical brighteners, luminophores, etc. Objective: The importance of these compounds stimulated the development of innovative conventional and modern catalytic methods for their preparation. The present review highlights recent progress in the above subjects

Background: Organic pollutants are common and exist widely in ecosystems, particularly in aqueous solution, and they are a serious threat to humans. Many technologies have been applied to wastewater treatment, and adsorption is a good method for organic pollutant removal that has been universally applied. Cyclodextrins (CDs) are excellent adsorbents due to their unique cavity, which can form stable inclusion complexes with some pollutants, and they are low-cost, non-toxic and renewable. Because cyclodextrins are greatly soluble in water, the actual application of cyclodextrin-based adsorbents was designed by crosslinking or immobilizing the CDs. Objective & Methodology: This article details synthetic methods for various cyclodextrin-based adsorbents and summarizes the information about the broad applications of cyclodextrin-based adsorbents for the removal of different substances and studies of better fixed kinetic and isotherm models for the adsorption process. We also provide a possible mechanism of adsorption. In addition, the effects of various operational parameters are summarized, including the pH, initial pollutant concentration, adsorbent dosage and ionic strength. Finally, the advantages and disadvantages of the adsorption of organic pollutants on cyclodextrin-based adsorbents and some advice for future studies are proposed. Many papers have focused on cyclodextrin-based adsorbents and that proved they are excellent. However, few articles have reviewed the use of cyclodextrin for the adsorption of organic pollutants.

Background: 2-Substituted benzoxazoles and their various derivatives are very important structures of functional materials, such as natural products, drug candidates, and biologically relevant compounds. Furthermore, they are multifunctional intermediates and synthons in a large number of functional group transformations and total syntheses. In last several decades, chemists have put forth tremendous effort and progress in the development of synthetic procedures for 2-substituted benzoxazoles preparation and applications in synthetic and medicinal field. Methodology: Catalytic synthesis of 2-substituted benzoxazoles can be classified into metal- and nonmetalcatalyzed processes simply. In the study of metal catalysis, the reactions are mainly performed using copper, palladium, iron, ruthenium, iridium; whereas, other metals such as zinc, cobalt, silver, gold based catalysts have also been explored to some extent. On the other hand, nonmetal-catalyzed 2-substituted benzoxazoles syntheses are generally restricted to Brønsted acid catalysts in the presence of or without other promoters. Objective: In this review, we are going to highlight the recent important research endeavors which are related to catalytic 2-substituted benzoxazoles synthesis.

Background: Chiral peroxides, many of which are biologically active, are an attractive target in organic synthesis. Organocatalysts have been used for some time in the asymmetric epoxidation of α,β- unsaturated carbonyls. More recently, cinchona-derived organocatalysts have been adapted to effect the asymmetric peroxidation of unsaturated ketones. We successfully applied this catalyst system to the stereoselective peroxidation of more challenging α,β-unsaturated aldehydes with moderate enantioselectivity observed. Herein we describe our efforts to improve upon the overall stereoselectivity using prolinol-derived organocatalysts. Objective: To determine whether diarylprolinol silyl ethers are effective catalysts in the asymmetric peroxidation of α,β-unsaturated aldehydes. Methods: Using trans-2-butenal as the test substrate, peroxidation with tert-butyl hydroperoxide was attempted in a range of different solvents. The resulting β-peroxyaldehydes were oxidised in situ to afford stable β-peroxyesters. The reaction was further optimised by varying the co-catalyst and by changing the silyl ether group on the prolinol catalyst. A number of short-chain substrates were subjected to peroxidation under optimised conditions. Results: Diarylprolinol ethers were found to be effective catalysts for the enantioselective peroxidation of unsaturated aldehydes. The degree of enantioselectivity was influenced both by the choice of solvent and acid cocatalyst. Furthermore, a clear trend emerged where the level of enantioselectivity increased with increasing steric bulk of the silyl group. Conclusion: Diarylprolinol ethers are effective catalysts for the asymmetric peroxidation of α,&#β ;-unsaturated aldehydes. Under optimised conditions, short-chain substrates may be converted to the corresponding &#β ;- peroxyesters in good yields and excellent enantioselectivities.

Background: In the quest for sustainable energy materials, new donor and acceptor materials are being designed, synthesized and tested for photovoltaic (PV) applications. In this context, conjugated organic polymers have received significant interests in the last few decades. Objective: In the present work, we synthesized an organic poly-yne P and assessed its efficiency as donor with a rylene acceptor EP-PTC. Methods: The organic poly-yne P was synthesised via Sonogashira coupling and characterized by analytical and spectroscopic techniques. The PV performance of blends composed of different amounts of polymer P and acceptor EP-PTC was assessed. Computational studies were undertaken at DFT level to determine the geometry, dipole moment, Mulliken charge and energy level. Results: A soluble blue low band-gap (1.72 eV) π-conjugated co-polymer consisting of dioctyloxyphenylene unit linked via ethynylene to 2,3-diphenylthieno[3,4-b]pyrazine has been synthesized and characterized. Blends of P and a soluble organic dye EP-PTC showed good PV performance with broad photocurrent spectra. The copoly-yne/dye-based solar cell with high EP-PTC content shows significantly higher external quantum efficiency (EQE) compared to the single material-based devices. However, a decrease in EQE was observed upon thermal annealing. DFT calculations showed convergence of the experimental results. Conclusion: We have synthesized and characterized a thienopyrazine-based organic co-polyyne and showed that blends of co-polymer P and the perylene dye EP-PTC possess high EQE up to 5.5% for the 90:10 EPPTC: P blend at wavelengths between 350 nm and 710 nm.