Current Organic Chemistry - Volume 22, Issue 6, 2018

Knoevenagel condensation was discovered in the 20th century, and since then it has been present in a wide range of reactions in organic chemistry due to its potential for forming carbon-carbon bonds. This reaction is usually carried out between aldehydes or ketones and active methylene compounds in the presence of Lewis acids or basic catalysts. The great advantage of this reaction is that can be carried out in mild conditions, with easy handling and using solvents with low toxicity. In the last 15 years, this type of organic synthesis has been used for the formation of α,β- unsaturated carbonyl compounds according to the principles of Green Chemistry. The use of microwave radiation to perform Knoevenagel condensation reactions is today a reality due to their ability to reduce the reaction time from hours to minutes, absence of unwanted products and free-solvent reactions. In this article we will review and discuss a collection of these reactions under microwave radiation dividing it into two strands. The first presents the condensation of Knoevenagel between malononitrile and aldehydes and the second one, addresses the alternatives to use malononitrile-derivatives such as cyanoacetamides and cyanoacetates. The Knoevenagel adducts formed from aldehydes present excellent results in terms of reaction yield (above 90 %) in short reaction times (<10 min). The authors left their contributions in order to corroborate with this complete analysis on the new trends of this subject with great potential on Green Chemistry.

In the last two decades, considerable attention was devoted to the use of ionic liquids (ILs) in organic syntheses. Initially, they were applied as solvents, often playing the role of the catalyst as well. Nowadays, there is a growing trend to apply the ILs as cosolvents, additives, or catalysts in organic reactions. The spread of ILs justified several reviews on reactions carried out in the presence of different ILs. However, there is no sharp line between the cases, when the IL is used as a solvent, or only as a catalyst. This review aims at summarizing the examples of organic syntheses promoted by a catalytic amount of an IL, and highlighting the typical IL-catalyzed reactions.

Catalytic asymmetric hydrosilylation based on the use of inexpensive and handleable hydridic silanes is a very useful reaction in organic chemistry which has become the subject of special interest because of the intrinsic peculiarity of economic efficiency and environmental friendliness. Recently, a lot of structurally diverse organocatalysts have been designed and applied to this chemistry. Enantiopure organocatalysts such as formamide derivatives, picolinamide derivatives, S-chiral sulfinamide derivatives and chiral frustrated Lewis pairs (FLPs) have been proved as privileged catalysts for the enantioselective hydrosilylations. This manuscript provides an overview on the most relevant advances in this field and presents an extensive summary of the catalysis performance of the above mentioned catalysts.

Background: Ammonium bifluoride is a reagent widely used in organic synthesis; however, the systematic collection and classification have not been covered until now. Methodology: In this review, we aim to systematically summarize the application of ammonium bifluoride in organic synthesis. Conclusion: It can be used for deprotection of hydroxyl protected groups (esp. Silyl protection). It is also used for introducing F & N atoms into organic molecules; promoting cyclization reactions acting as a multifunctional reagent.

Background: Dendritic self-host phosphorescent Iridium materials, which generally consist of an Iridium light-emitting core, dendrons(branches) and surface groups, are a kind of novel and effective triplet emission materials for non-doped solutionprocessed organic light-emitting diodes (OLEDs). Methodology: Iridium light-emitting cores can harvest singlet and triplet excitons to obtain a theoretical internal quantum efficiency of 100% and can be chosen to determine key photoelectric properties, such as color of light emission. Peripheral dendrons can act as a host of an emissive core. The shielding effect can also reduce or eliminate the interactions between the emitting phosphors and prevent luminance quenching. Conclusion: Surface groups can provide suitable solubility for dendrimers in organic solvents. Therefore, phosphorescent dendrimers are applicable to highly efficient self-host solution-processed OLEDs.

Dendrimers are a kind of macromolecule materials composed of central nuclei, repeating units and terminal groups. The dendritic topology leads to unique threedimensional architecture with mono-distribution at the nano-scale. Considerable attention has been focused on the high-efficient synthesis and potential applications of dendrimer in various fields such as biomedicine, catalysts, membrane materials and biosensors. Due to the precise structure and the abundant surface functional groups, dendrimers are useful biomedical materials. This review summarizes the present condition and development of the versatile dendrimers as biomaterials. We discuss synthetic methods, including divergence and convergence method, click reaction method, one pot method and supramolecular self-assembly method as well as the biomedical application such as tissue engineering, drug and gene delivery, biomedical imaging and sensing of dendrimers.

An efficient protocol for the intermolecular amidoselenation of alkenes with diphenyl diselenides and acetonitrile has been developed that affords a series of β-amidoselenides in high yields under mild conditions. The preliminary experimental results support the involvement of active benzyl radical species, and a radical pathway was therefore proposed for the reaction.