Mini-Reviews in Organic Chemistry - Volume 15, Issue 4, 2018

N-Heterocyclic carbenes (NHCs) as one of the most powerful reagents, ligands and organocatalysts for various reactions have been widely used in modern synthetic applications. Especially, the chiral NHCs have attracted intense attention in stereoselective reactions from synthetic chemists based on their highly efficiency and unique catalytic properties with excellent diastereoselectivity and enantioselectivity. A great deal of exciting achievements in the synthesis and applications of chiral NHC catalysts have been attained over the past decades. This review will mainly summarize recent advances in the chiral NHC-catalysed stereoselective reactions according to the use of NHCs including the generation of equivalents acyl anions, homoenolates, azolium enolates/acyl azoliums and oxidative NHC catalysis.

Phosphorescent Organic Light-Emitting Diodes (PHOLEDs) have an advantage of stability for a lifetime in comparison with the conventional Organic Light-Emitting Diodes (OLEDs). Green and red OLEDs have already achieved success, but for the last decade, blue OLEDs have observed a surge in the attention towards them from academia as well as the industry. There are incessant efforts devoted towards the improvement of external quantum efficiency from 25-30%. The host materials (or host compounds), hole transporting and electron transporting are the preeminent factors for the enhancement of External Quantum Efficiency (EQE). This review aims at highlighting the role of pyridine as an efficient Electron Transporting Material (ETM) for blue PHOLEDs. Pyridine having electron withdrawing nature can serve as valuable host compounds for electron transport material in PHOLEDs of a blue color. The presence of nitrogen atom in pyridine facilitates in lowering HOMO/LUMO energy levels compared to benzene ring and this assists in adding phenyl rings at the periphery of pyridine ring.

As a sub-group of the cucurbituril family, hemicucurbiturils have become increasingly prominent as a new platform in host-guest chemistry. Their flexible structures, due to only one methylene chain bridging the urea moieties, endow them with different properties to those of cucurbiturils, such as solubility in common organic solvents, accommodation of anions in their cavities, and so on. In this review, we survey the synthesis of hemicucurbiturils and their derivatives involving cyclohexylhemicucurbiturils, bambusurils, and biotinurils, as well as their supramolecular properties of host-guest interactions, molecular recognitions, and supramolecular catalysis. The review aimed to achieve a comprehensive understanding of the new class of macrocylic compounds for both investigators already engaged in this research field and those interested in gaining insight into these macrocycles.

The coupling reaction of terminal alkynes and CO2 provides a promising way to synthesize propiolic acids. Among the existing catalytic systems, transition-metal copper and silver exhibit excellent catalytic efficiency under mild conditions probably being attributed to the activation of C-C triple bond of terminal alkynes. In this aspect, efficient strategies for activating both substrate and CO2 are often smart choices. This review summarizes the development trend of the Cu/Ag-catalyzed carboxylation reactions of terminal alkynes with CO2, and representative examples are also discussed in detail.

Triazole ring system has attracted a continuously growing interest of synthetic organic chemists and medicinal chemists due to its versatile potential to interact with biological systems. This review article presents an update of new methods, synthetic strategies explored for the synthesis of triazoles having antimicrobial and antitubercular activities.

2-Oxazolidones are an important class of nitrogen-containing heterocyclic compounds, which have been found to have a wide range of applications as chiral auxiliaries and chemical intermediates in organic synthesis. Moreover, some 2-oxazolidones such as linezolid, toloxatone, and tedizolidare are shown to have high potency as biologically active molecules and are widely used in the pharmaceutical industry. Therefore, many efforts have been dedicated to synthesize these useful cores. Among recent reported synthetic methods, the carboxylative cyclization reactions of inexpensive and easily available allylic and 2,3-allenic amines with CO2 are one of the most interesting and promising synthetic procedures from the viewpoint of developing CO2 as carbon source, since the chemical conversion of CO2 into the value-added chemicals is one of the most important topics in green and sustainable chemistry. In this mini review, we highlight the advances in the synthesis of 2-oxazolidone derivatives through chemical fixation of CO2 to allylic and 2,3-allenic amines from 1987 to 2017, with special emphasis on the mechanistic aspects of the reactions.

The kinetics of different reaction systems were reviewed for the phase-transfer catalysis under microwave (MW) irradiation conditions. The different factors on the reaction kinetics were reviewed. The advantages of chemical reaction / conversion under MW irradiation conditions were highlighted. Notably these reactions avoid longer reaction times, enhance the product yield and reduce the organic solvent. Developments of this methodology and selectivity of different reactions were presented.

Leishmaniasis is a neglected tropical disease caused by around 20 species of obligate intramacrophage protozoa of the genus Leishmania. This disease is an important cause of morbidity and mortality that primarily impacts the poorest populations living in tropical and sub-tropical regions of the world, but has become of concern in some developed countries. The resistance of leishmanial parasites to the drugs available and their undesirable side effects have prompted the discovery of new synthetic compounds with potent antileishmanial activity and fewer side effects that can serve as new therapeutic agents. In this article, we make a comprehensive review of the most recent advances of synthetic compounds with antileishmanial activity (from 2015 to the early 2017). Furthermore, we covered the structure- activity relationship studies that allow for optimization and selection of the most promising drugs, and the biochemical mechanisms that explain the antileishmanial activities observed.