Electrochemical Oxidative Csp3—H/S—H Cross‐Coupling with Hydrogen Evolution for Synthesis of Tetrasubstituted Olefins

Tetrasubstituted olefins are significant scaffolds as they are prevalent in many biologically active compounds and versatile building blocks for organic synthesis. Herein, we report an electrochemical oxidative Csp³—H/S—H cross‐coupling reaction, in which various tetrasubstituted olefins were prepared under base‐free, transition metal‐free, and oxidants‐free reaction conditions.     

Asymmetric Pd(II)-Catalyzed C−O,C−N,C−C Bond Formation Using Alkenes as Substrates: Insight into Recent Enantioselective Developments

This Review summarizes the advances in the catalytic enantioselective mono- and difunctionalization of alkenes, highlighting the fundamental role of ligands. Several types of asymmetric reactions have been developed involving different bonds formation, C−O, C−N and C−C, highlighting the urgency to go ahead in the search for new ligands and synthetic methodologies in order to improve the control over the reaction selectivity and activity and thus, to increase the applications in the synthesis of heterocyclic scaffolds and biologically active compounds. The Review is organized into paragraphs, which discuss the type of bond formed during the nucleopalladation, C−O, C−N, C−C bonds, and the type of reaction involved.     

Recent Advances in Chemistry of Condensed 4‐Thiazolidinones

The syntheses of condensed 4‐thiazolidinone and its various derivatives are reviewed for the first time. Condensed 4‐thiazolidinones are important scaffolds and versatile substrates in heterocyclic chemistry, as they can be used for the synthesis of a large variety of biologically active compounds such as thiazolotriazines and as raw material for the drug synthesis. The high reactivity of active methylene group next to the carbonyl of the thiazolidin ring represents useful targets for many organic reactions.     

Copper-catalyzed annulation of 2-bromobenzoic esters with terminal alkynes towards 3-substituted isocoumarins

An efficient method for the synthesis of 3-substituted isocoumarins that are an important class of biologically active scaffolds via annulation of 2-bromobenzoic esters with terminal alkynes by copper catalyzed is described. The advantages of this method include mild reaction conditions, high yield and regioselectivity, and wide tolerance toward functional groups.     

Synthesis of Heterocycles from 2-Acylbenzoic Acids

Heterocyclics are the crucial scaffolds present in pharmaceuticals, natural products, biologically active compounds and agrochemicals. Consequently, the development of simple and practical methods for constructing heterocyclics has always been a fascinating field in organic synthesis. Recently, 2-acylbenzoic acids, highly reactive and versatile synthons, have been broadly applied in the construction of heterocycles due to their multiple reaction sites. In this review, we summarized recent progress in the application of 2-acylbenzoic acids for the synthesis of heterocycles including phthalides, isochromanones, isoindolines, phthalazinones, and quinolones. The substrate scopes, proposed mechanisms, and product application of different types of reactions are discussed.     

An efficient protocol for the synthesis of benzoheterocyclic compounds via solid-state melt reaction (SSMR)

An efficient protocol for the synthesis of biologically active benzoheterocyclic compounds such as benzothiazoles, benzimidazoles, benzospirothiazoles, and quinoxaline scaffolds have been accomplished via solid state melt reaction (SSMR) with excellent yields. The new protocol does not require any catalyst, solvent, and workup. Two anti-tumor agents have been prepared to demonstrate the application of this new method.     

Direct C-H cross-coupling approach to heteroaryl coumarins

A Pd-catalyzed direct cross-coupling of 3-bromocoumarins with heteroarenes provided an efficient route to synthesizing 3-heteroarylcoumarins. The reaction scope for the transformation was fairly broad, affording modest to good yields of various 3-heteroarylcoumarin scaffolds, which are privileged structures and prevalent motifs in many biologically active compounds and fluorophores.     

Substituted Pyrazoles and Their Heteroannulated Analogs—Recent Syntheses and Biological Activities

Pyrazoles are considered privileged scaffolds in medicinal chemistry. Previous reviews have discussed the importance of pyrazoles and their biological activities; however, few have dealt with the chemistry and the biology of heteroannulated derivatives. Therefore, we focused our attention on recent topics, up until 2020, for the synthesis of pyrazoles, their heteroannulated derivatives, and their applications as biologically active moieties. Moreover, we focused on traditional procedures used in the synthesis of pyrazoles.     

(S)-4-(4-aminobenzyl)-2-oxazolidinone based 2-azetidinones for antimicrobial application and luminescent sensing of divalent metal cations

The impact of linezolid as an antibiotic against gram-positive bacteria has inspired synthetic chemists to use oxazolidinones as substrate molecule in the synthesis of newer scaffolds with important pharmacological implication. The oxazolidin-2-ones are key intermediates in the synthesis of many interesting biologically active compounds. Design and synthesis of a new series of (S)-4-(4-aminobenzyl)-2-oxazolidinone based multifunctional azetidinones were accomplished. Synthesis of the scaffolds was performed through a multi-step reaction process involving protection of amine functional group, conversion of protected (S)-4-(4-aminobenzyl)-2-oxazolidinone to its acetic acid derivative and then to acid chloride, and finally coupled with different substituted aromatic imines under mild reaction conditions in presence of an appropriate base. Structural characterization was carried out using conventional spectroscopic techniques. The compounds were screened for their antimicrobial activity against gram-positive and gram-negative bacteria and were found to possess better and promising antimicrobial property than some of the reported antimicrobial drugs like disulfonamide and tetracycline. Additionally, the scaffolds also exhibit prominent sensing property for divalent metal cations like Cu²⁺, Zn²⁺, and Ni²⁺, through fluorescence quenching effect.     

Copper Catalysis and Organocatalysis Showing the Way: Synthesis of Selenium‐Containing Highly Functionalized 1,2,3‐Triazoles

This article provides a comprehensive overview of reported methods ‐ particularly copper‐ and organocatalyzed reactions ‐ for the regioselective syntheses of selenium‐containing 1,2,3‐triazoles systems. These chemical entities are prevalent cores in biologically active compounds and functional materials. In view of their unique properties, substantial efforts have been paid for the design and development of practical approaches for the synthesis of these scaffolds.     

Application of magnetically recoverable nanocatalysts in synthesis of imidazole,thiazole, and oxazoles

Abstract

Imidazoles, thiazoles, and oxazoles have been identified as valuable molecules in pharmaceutical and agriculture chemistry. Molecules containing these scaffolds are excited in many natural products and biologically active molecules. During the last decade, magnetic nanomaterials have appeared as highly efficient catalysts in chemical science in general organic chemistry, because of their simple preparation, modification, and large surface area ratio. This article assists to review the application of magnetically reusable nanocatalysts in synthesis of biologically active imidazoles, thiazoles, and oxazoles.     

Samarium diiodide induced ketyl-(het)arene cyclisations towards novel N-heterocycles

In this tutorial review we discuss recent advances in the field of ketyl-(het)arene cyclisations promoted by samarium diiodide and related processes. Couplings of samarium ketyls with carbon-carbon multiple bonds are perhaps the most useful reactions to create carbocycles and heterocycles of various ring sizes. They have also successfully been exploited for the synthesis of biologically active compounds or natural products. In this article we intend to summarise our diversity orientated approaches towards nitrogen heterocycles and emphasize other approaches with SmI(2) as well as electrochemical cyclisation methods providing similar N-heterocycles. We also briefly discuss our recently published formal total synthesis of strychnine employing a new samarium diiodide induced cascade reaction as key step. All these examples demonstrate the high synthetic potential of samarium ketyl-(het)arene cyclisations for the preparation of various types of important heterocyclic compounds.     

Synthesis of diverse heterocyclic scaffolds via tandem additions to imine derivatives and ring-forming reactions

A novel strategy has been developed for the efficient syntheses of diverse arrays of heterocyclic compounds. The key elements of the approach comprise a Mannich-type, multicomponent coupling reaction in which functionalized amines, aromatic aldehydes, acylating agents, and π- and organometallic nucleophiles are combined to generate intermediates that are then further transformed into diverse heterocyclic scaffolds via a variety of cyclization manifolds. Significantly, many of these scaffolds bear functionality that may be exploited by further manipulation to create diverse collections of compounds having substructures found in biologically active natural products and clinically useful drugs. The practical utility of this strategy was exemplified by its application to the first, and extraordinarily concise synthesis of the isopavine alkaloid roelactamine.     

Investigation of innovative synthesis of biologically active compounds on the basis of newly developed reactions

Synthesis of biologically active compounds, including natural products and pharmaceutical agents, is an important and interesting research area since the large structural diversity and complexity of bioactive compounds make them an important source of leads and scaffolds in drug discovery and development. Many structurally and also biologically interesting compounds, including marine natural products, have been isolated from nature and have also been prepared on the basis of a computational design for the purpose of developing medicinal chemistry. In order to obtain a wide variety of derivatives of biologically active compounds from the viewpoint of medicinal chemistry, it is essential to establish efficient synthetic procedures for desired targets. Newly developed reactions should also be used for efficient synthesis of desired compounds. Thus, recent progress in the synthesis of biologically active compounds by focusing on the development of new reactions is summarized in this review article.     

Asymmetric Alkynylation/Lactamization Cascade: An Expeditious Entry to Enantiomerically Enriched Isoindolinones

An unprecedented Cu^I–pybox‐diPh‐catalyzed highly enantioselective (up to >99 % ee) alkynylation/lactamization cascade has been developed as a general catalytic system for the synthesis of diversely substituted isoindolinones of immense biological importance. The cascade effects one C? C and two C? N bond‐forming events in one reaction vessel under operationally simple, additive‐free reaction conditions in good to excellent yields. The methodology was further extended to the synthesis of tetrahydroisoquinoline scaffolds common to several biologically active natural products in a two‐step sequence with remarkable selectivity (up to 94 % ee).     

Streamlined Synthesis of Diaminopyridines by Pd-Catalyzed Ammonia Coupling with Deactivated Amino-Chloropyridines

An efficient and cost-effective two-step synthesis of diaminopyridines, fundamental building blocks of biologically active compounds, is reported. The advantages over previously reported routes include cost and wider availability of the bromo-chloropyridine starting materials and the straightforward accessibility to an extended array of diaminopyridine regioisomers. The key enabler of this synthetic strategy is the development of an unprecedented palladium-catalyzed coupling reaction of ammonia with chloropyridines deactivated by the presence of an alkylamino substituent. The coupling reaction was accomplished with very low catalyst loadings under remarkably mild reaction conditions, making the system particularly suitable for both academic and industrial applications. The utility of this methodology is exemplified by the application to the synthesis of highly relevant scaffolds, including the synthetic intermediates of the marketed drugs Ribociclib and Palbociclib.     

Recent synthetic methodologies for pyridopyrazines: An update

Abstract

Among heterocyclic compounds, pyridopyrazines are the scaffolds that have gained considerable attention on academic and industrial level due to their widespread applications as intermediates in the preparation of advanced and biologically potent pharmaceutical materials. Many pyridopyrazine derivatives are available in market to cure various pharmacological disorders. These candidates can be synthesized via a number of synthetic routes using various reagents like cyclocondensation of diaminopyridines with carbonyl compounds or their derivatives etc. In the present review, we have elaborated all these protocols along with different factors and reaction conditions such as use of metal catalyst, solvent-free and microwave irradiation, one-pot synthesis etc. that have resulted in high regioselectivity and yields. The review focuses on the synthetic methodologies developed in the last decade for different pyridopyrazine derivatives.     

A practical synthesis of differentially protected 2-(hydroxymethyl)piperazines

An efficient and scalable synthesis of three differentially protected 2-(hydroxymethyl)piperazines is presented, starting from optically active and commercially available (2S)-piperazine-2-carboxylic acid dihydrochloride. These synthetic building blocks are useful in the preparation of biologically active compounds and as chemical scaffolds for the construction of combinatorial libraries.     

Pd‐NHC catalysed Carbonylative Suzuki coupling reaction and its application towards the synthesis of biologically active 3‐aroylquinolin‐4 (1H)‐one and acridone scaffolds

We have unfolded a convenient and mild protocol for the synthesis of diaryl ketones via Pd‐ NHC catalysed carbonylative Suzuki coupling reaction. Notably, this method offers advantages like no use of toxic CO gas, shorter reaction time, high yield, and broad substrate scope. Several sensitive functional groups (like‐COMe, ‐COOMe, ‐F, ‐Cl, ‐Br, ‐NH₂, ‐CN) are well tolerated in this reaction. In addition, we have also demonstrated a new efficient route for the synthesis of biologically active and pharmaceutically important 2‐substituted 3‐Aroylquinolin‐4(1H)‐ones and acridone scaffolds.     

Palladium-catalyzed intramolecular CH acylation of indoles with thioester

A palladium-catalyzed intramolecular CH acylation of indole with thioester is described, providing a direct and effective approach for the synthesis of the biologically active indole-indolone scaffolds. The method obviates the need for the prefunctionalized starting materials including organometallic reagents, alkyl halides, and NHP esters in previous metal-catalyzed cross-coupling reaction with thioester. Substrates bearing sensitive halo groups are compatible in the reaction, leaving a functional handle for further structural elaborations.