Current Organic Chemistry - Volume 26, Issue 13, 2022

Over the last few decades, ionic liquids have been raised as a great appliance to pursue many organic transformations. In the present research, the synthetic application of ILs has emerged largely as solvents, additives, or catalysts. With the developing commercial methods, task-specific ionic liquids have been constructed by appointing guanidine, amidine and other superbasic cations. By the nature of the cation or the anion, the properties of the ionic liquids can be adjusted. In this regard, superbasic ionic liquids have been derived from both acyclic and cyclic guanidine or amidine derivatives. In particular, some common super bases such as 1,1,3,3-tetramethylguanidine (TMG), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), are used to design these special type of ionic liquids. These superbasic ionic liquids have shown a potential activity to accelerate many organic transformations including alcoholysis, esterification, multi-component reaction, Knoevenagel reaction, Michael addition, cyclization, etc. Additionally, because of their novel properties including high liquid range, nonvolatility, high thermal and chemical stability, these classic ionic liquids have a potential environmental impact and they are often found to play a promising role in the field of catalysis, electrochemistry, spectroscopy, and materials science. Not only that, the application of superionic liquids has been widely spread in the industrial and research area, especially, for the chemical transformation of CO2. This review aims to portray an outlook on the organic syntheses that have been promoted by superionic liquids in the last five years.

The Michael addition is an important, highly efficient, and atom-economical method for the diastereoselective and enantioselective C-C bond formation. MA used in the synthesis of natural products and drugs is referred to as tandem sequenced reaction. An important tandem sequence of Michael and Aldol additions is the Robinson annulation. MA is a versatile reaction employed for efficient bond formation between electron-poor olefins as Michael acceptors and varied nucleophiles as Michael donors. Apart from being involved in C-C bond formation, MA is also employed in the formation of C-X bond (X=O, N, S, P, etc.), giving rise to oxa-, aza-, thia-, and phospha-Michael addition products. In recent years many articles have been published on MA. The mechanism of MA gives an insight into the reaction initiated by the base. The present review provides comprehensive information on recent advancements in base-assisted Michael addition reactions, including varied organic and inorganic bases, such as 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU), 1,4-Diazabicyclo[2.2.2]octane (DABCO), 4-dimethylaminopyridine (DMAP), triethylamine (Et3N), tributylamine (Bu3N), N,N-diisopropylethylamine (DIEPA), diethylamine (NHEt2), guanidine derivatives, and bifunctional thiourea. A variety of inorganic bases, including metal alkoxides, metal acetates, metal hydroxides, metal hydrides, metal carbonates, metal halides, and triphenylphosphine (TPP), can also be successfully used in Michael reactions.

Chitosan (CS) is a crustacean-derived bio-macromolecular base. Physico-chemical properties of CS resemble cellulose, and the chemical structure constitutes β-(1-4)-linked Dglucosamine and N-acetyl-D-glucosamine units. It has tunable characteristics such as molecular weight, degree of acetylation, and acetyl distribution. It is proven to be a good support in making catalysts and functional materials. This article comprises the recently published articles using CS-based composites as heterogeneous catalysts in numerous chemical transformations of industrial relevance. In this connection, the CS-based composite materials have been successfully used as heterogeneous catalysts in a wide range of organic transformations, including cycloaddition, trimethylsilylation, cyanation, Suzuki-Miyaura, Heck, Beckmann rearrangement, O-carboxymethylation, nitroarenes reduction, nucleophilic acylation (phenyl acetates from acid chlorides), Knoevenagel condensation, biomass valorization, P–O bond formation, imination, dipolar addition, and multicomponent reactions. The CS has also been used to prepare magnetic nanocompositebased catalysts that showed easy separation and high reusability. This article is highly helpful in designing further chemical transformations where the role of the bio-polymeric base, CS may be critical.

Rearrangement reactions of organic substrates is a versatile and sustainable tool in the construction of complex and bioactive organics by virtue of their atom-economic, stepeconomic and waste-, time- as well as energy-minimizing attributes. The X → C (or Y) aryl rearrangement reaction through an intramolecular nucleophilic aromatic substitution is referred to as Smiles rearrangement. The Smiles rearrangement enables access to complex natural products and is a useful tool to obtain various types of compounds with diversified applications, which have undergone a potent revival in recent years. In this review, we summarize the recent reports on Smiles rearrangement and most of them require a base. A few examples of the reported base-free Smiles rearrangements were also reviewed to provide comprehensive information on the selected topic. The literature review covers the published work on Smiles rearrangement reaction since 2017. The published work in these articles include simple Smiles, Truce-Smiles, radical Smiles, Ugi-Smiles, light-assisted Smiles, Dohmori-Smiles, electrochemical Smiles and phospha-Smiles rearrangement reactions for the construction of a variety of organic compounds including acyclic, heterocyclic, carbocyclic and polycyclic compounds. The formation of organic compounds with unusual ring sizes has also been discussed in the published work. Several domono/sequential reactions were also observed in these reports involving Smiles rearrangement as a crucial step. The selected examples demonstrate the synthetic power of this approach and hence this review may be highly useful to the synthetic chemists aimed to use Smiles rearrangement in their plan.

The-C -C-bond-formation-via-the-cross-coupling-and-homocoupling-reactions-of organic-partners-are-central-to-the-synthesis-of-many-chemical-probes-and-have-valuable-applications in-the-medicinal-and-pharmaceutical-industries.-Polyaniline-(PANI)-is-the-most-useful performing-polymer-due-to-its-non-toxicity,-high-stability,-easy-synthetic-accessibility,-and simplicity-of-doping/dedoping-by-treatment-with-aqueous-acid-and-base.-PANI-plays-a-pivotal role-as-a-polymer-base-for-palladium-(Pd)-species-and-in-most-cases,-the-catalysts-showed-high yield,-reaction-transformation,-and-reusability.-In-this-review,-we-discuss-the-application-of-the Pdcommat;PANI-catalyst-for-cross-coupling/homocoupling-reactions,-analysis,-characterization,-and reusability.-We-covered-all-literature-about-Pdcommat;PANI-catalyst-functions-in-Suzuki-Miyaura, Heck,-Sonogashira,-and-Ullmann-coupling-reactions.