Synthesis Of Nitrogen Heterocycles Research Articles

Sodium Copper Chlorophyllin: A Sustainable Bioinspired Catalyst for the Aerobic Oxidative Synthesis of Nitrogen Heterocycles and the Oxidative Cyanation of Tertiary Amines

AbstractA remarkably simple and straightforward protocol has been reported showcasing sodium copper chlorophyllin (SCC) as an eco‐friendly, bioinspired catalyst for the aerobic oxidative synthesis of pharmaceutically prevalent nitrogen‐containing heterocycles, such as benzimidazoles and quinoxalines. This reaction was performed in green solvent water, using the green oxidant, molecular oxygen. SCC displayed exceptional efficiency, congruent with the prevailing metal/non‐metal‐based catalyst regime without requiring additives. The SCC catalyst exhibited excellent recyclability upto three cycles for the benzimidazole synthesis reaction. This benign strategy was successfully applied in synthesizing a bioactive quinoxaline i. e., Tyrphostin AG1296, a promising candidate for melanoma treatment. The catalytic activity of SCC was explored for the synthesis of another privileged moiety i. e., α‐aminonitriles, via the α‐cyanation of tertiary amines under oxidative conditions. This reaction progressed with a mild, easy‐to‐use, convenient cyanide source, such as ethyl cyanoformate, and a green and attractive solvent, such as methanol, precluding acidic media. SCC catalyst was efficiently recycled upto three cycles for the α‐aminonitriles synthesis. Overall, the utility of a biodegradable, robust catalyst such as SCC, eco‐friendly solvents such as water and methanol, green oxidants such as O2, and mild reaction conditions, devoid of acidic additives, renders the present work viable for academic and industrial research.

Electrochemical Generation of Nitrogen‐centered Radicals and its Application for the Green Synthesis of Heterocycles

AbstractElectrochemistry became a unique and powerful tool for the preparation of a plethora of valuable chemical species including functional materials, drug candidates and clinically approved pharmaceuticals. Organic electrosynthesis well satisfies main goals of green chemistry development and is considered as one of the useful approaches toward the creation of sustainable future. Since nitrogen heterocyclic scaffolds still retain their importance for the construction of novel materials and medications, one of the emerging trends in organic electrochemistry is the discovery of novel green and sustainable synthetic methods toward the assembly of heterocyclic subunits. In this regard, organic electrochemistry provides an efficient platform for environmentally benign generation of various nitrogen‐centered radicals which are prominent intermediates in the synthesis of nitrogen heterocycles. In this Review, recent developments in the creation of green synthetic methods for the construction of nitrogen heterocycles via electrochemical generation of nitrogen‐centered radicals are summarized. The special emphasis is devoted to the influence of solvent, electrodes and electrolytes on the electrochemical step, since these crucial parameters regulate the process efficiency.

Chemoenzymatic Synthesis of 2‐Aryl Thiazolines from 4‐Hydroxybenzaldehydes Using Vanillyl Alcohol Oxidases

AbstractNitrogen heterocycles are commonly found in bioactive natural products and drugs. However, the biocatalytic tools for nitrogen heterocycle synthesis are limited. Herein, we report the discovery of vanillyl alcohol oxidases (VAOs) as efficient biocatalysts for the one‐pot synthesis of 2‐aryl thiazolines from various 4‐hydroxybenzaldehydes and aminothiols. The wild‐type biocatalyst features a broad scope of 4‐hydroxybenzaldehydes. Though the scope of aminothiols is limited, it could be improved via semi‐rational protein engineering, generating a variant to produce previously inaccessible cysteine‐derived bioactive 2‐aryl thiazolines using the wild‐type VAO. Benefiting from the derivatizable functional groups in the enzymatic products, we further chemically modified these products to expand the chemical space, offering a new chemoenzymatic strategy for the green and efficient synthesis of structurally diverse 2‐aryl‐thiazoline derivatives to prompt their use in drug discovery and catalysis.

Chemoenzymatic Synthesis of 2-Aryl Thiazolines from 4-Hydroxybenzaldehydes Using Vanillyl Alcohol Oxidases.

Nitrogen heterocycles are commonly found in bioactive natural products and drugs. However, the biocatalytic tools for nitrogen heterocycle synthesis are limited. Herein, we report the discovery of vanillyl alcohol oxidases (VAOs) as efficient biocatalysts for the one-pot synthesis of 2-aryl thiazolines from various 4-hydroxybenzaldehydes and aminothiols. The wild-type biocatalyst features a broad scope of 4-hydroxybenzaldehydes. Though the scope of aminothiols is limited, it could be improved via semi-rational protein engineering, generating a variant to produce previously inaccessible cysteine-derived bioactive 2-aryl thiazolines using the wild-type VAO. Benefiting from the derivatizable functional groups in the enzymatic products, we further chemically modified these products to expand the chemical space, offering a new chemoenzymatic strategy for the green and efficient synthesis of structurally diverse 2-aryl-thiazoline derivatives to prompt their use in drug discovery and catalysis.

Asymmetric electrophilic functionalization of amino-substituted heteroaromatic compounds: a convenient tool for the enantioselective synthesis of nitrogen heterocycles.

The catalytic asymmetric electrophilic functionalization of the less reactive N-heteroaromatic compounds has been reported using the approach of the introduction of an exocyclic amino substituent. This strategy has allowed enantioselective Friedel-Crafts alkylation in pyrazoles, isoxazoles and isothiazoles, as well as in aminoindoles, aminobenzofurans and aminobenzothiophenes. Several stereoselective methods have been used for the 1,4-addition or 1,2-addition of these heteroaromatic compounds to different electrophiles employing organocatalysts or chiral metal complexes. The activating exocyclic amino substituent has also been used as a nucleophile in tandem reactions, including formal cycloadditions ([3+2] and [3+3]), for the synthesis of highly functionalized chiral nitrogen heterocycles.

Synthesis of Deuterated Enaminones with High Isotopic Fidelity.

The unexpected oxidation of nitrogenous heterocycles by aldehyde oxidase (AO) may be addressed by the substitution of deuterium for hydrogen adjacent to the heterocycle nitrogen atom. Enaminones are versatile intermediates in the synthesis of nitrogenous heterocycles. We report that heretofore inaccessible monodeuterated enaminones of the general structure RC(=O)CH=CDNMe2 may be synthesized from methyl ketones and DCO2Me with high isotopic fidelity and efficient utilization of deuterium.

Nitrogen Heterocycle Synthesis through Hydride Abstraction of Acyclic Carbamates and Related Species: Scope, Mechanism, Stereoselectivity, and Product Conformation Studies.

Acyliminium ions and related species are potent electrophiles that can be quite valuable in the synthesis of nitrogen-containing molecules. This manuscript describes a protocol to form these intermediates through hydride abstractions of easily accessible allylic carbamates, amides, and sulfonamides that avoids the reversibility that is possible in classical condensation-based routes. These intermediates are used in the preparation of a range of nitrogen-containing heterocycles, and in many cases high levels of stereocontrol are observed. Specifically areas of investigation include the impact of chemical structure on oxidation efficiency, the geometry of the intermediate iminium ions, the impact of a substrate stereocenter on stereocontrol, and an examination of transition state geometry.

N-Aryl Amino Acids as Potential Antibacterial Agents

The resistance of bacteria to current antibiotic drugs and the re-occurrence of different ailments after several therapeutic protocols continue to be a cause for concern. Arylated amino acids are vital synthons to many compounds; they serve as essential building blocks in the synthesis of nitrogen heterocycles with various biological activities. This research reports on the synthesis of some N-aryl amino acids and evaluates their antibacterial activities. The N-aryl amino acids 3a–3j were obtained by reacting different 4-substituted fluorobenzene 1a–1d with different amino acids 2a–2g via a metal-free base-induced aryl amination reaction of aryl halides. The antibacterial activities of the synthesized compounds were evaluated against eight bacterial strains (Four Gram-positive, Bacillus subtilis (ATCC 6633), Streptococcus pneumonia (ATCC 33400), Staphylococcus aureus (ATCC 25923), and Staphylococcus epidermidis (ATCC 14990), and four Gram-negative, Enterobacter cloacae (ATCC 43560), Escherichia coli (ATCC 25922), Proteus mirabilis (ATCC 43071), and Klebsiella oxytoca (ATCC 13182) using the agar well diffusion method with streptomycin as a reference drug. The biological screening indicates that the synthesized compounds 3a, 3e, and 3j have promising broad-spectrum antibacterial potential, as the N-aryl amino acid displayed activity that was comparable to the standard drug against Streptococcus pneumonia, Escherichia coli, and Proteus mirabilis.

Site‐Selective Decarboxylative Direct Formylation of Nitrogen Heterocycles (Azaindoles, Indoles, Pyrroles) and Anilines Utilizing Glyoxylic Acid

AbstractA new method for formylation of nitrogen heterocycles overcoming the limitations of classical approaches using a cheap feedstock formylating agent especially under mild and neutral conditions is the subject of this current investigation. This work describes direct formylation of nitrogen heterocycles (azaindoles, indoles, pyrroles) and anilines using glyoxylic acid as the formyl source and K2S2O8 as the exclusive reagent. The key features include a general method for both C‐ and N‐formylation under neutral and mild reaction conditions. The application of the method is further demonstrated in the tandem synthesis of nitrogen heterocycles, pharmaceuticals, and a natural product. Unlike aroylation with arylglyoxylic acids, a previously unknown pathway for the direct formylation with glyoxylic acid in the presence of K2S2O8 is now unveiled.magnified image

Recent Advances in the Synthesis of Nitrogen Heterocycles Using β-Nitrostyrenes as Substrates

Abstract:: The exploration of synthetic methodologies that allow rapid access to a wide variety of N-heterocycles is of critical importance to the medicinal chemist as it provides the ability to expand the available drug-like chemical space and drives more efficient drug discovery programs. β-Nitrostyrenes, as unique active intermediates, have been widely applied in synthetic organic chemistry because of their versatile utility as pharmaceutical agents and agrochemicals. In this review, we summarize the recent development and application of the elegant and efficient methods that enable the concise synthesis of N-heterocycles from β-nitrostyrenes and various partners in a step- and atom-economic manner, including cascade reactions, C-H activation, regio- and stereoselective syntheses, as well as other novel syntheses, which will potentially provide useful insights for further exploring and designing novel reactions.

Silver-catalyzed synthesis of nitrogen heterocycles: recent advancements.

Heterocyclic chemistry is an ever-expanding field without boundaries. Heterocycles play a significant role in medicinal and pharmaceutical chemistry, the agricultural industry and materials science. Among heterocycles, N-heterocycles constitute a large family. Their ubiquity in living and non-living systems makes them an endless topic for research. Being a part of the research community, we need to balance environmental concerns with scientific and economic development. So, research that is coherent with nature is a trending domain at all times. Silver catalysis possesses a greener face in organic synthesis. The simple, rich and extensive chemistry shown by silver makes it an attractive choice for catalysis. Inspired by its versatility and uniqueness we have compiled here recent developments in the silver-catalyzed synthesis of nitrogen-containing heterocycles since 2019. The high efficiency, regioselectivity, chemoselectivity, recyclability of the catalytic system, greater atom economy and simple reaction setup are the major highlights of this protocol. It is a hot research topic which is evident from the large number of works carried out for the fabrication of a range of N-heterocycles with varying complexities.

Synthesis of Stereoenriched Piperidines via Chemo-Enzymatic Dearomatization of Activated Pyridines.

The development of efficient and sustainable methods for the synthesis of nitrogen heterocycles is an important goal for the chemical industry. In particular, substituted chiral piperidines are prominent targets due to their prevalence in medicinally relevant compounds and their precursors. A potential biocatalytic approach to the synthesis of this privileged scaffold would be the asymmetric dearomatization of readily assembled activated pyridines. However, nature is yet to yield a suitable biocatalyst specifically for this reaction. Here, by combining chemical synthesis and biocatalysis, we present a general chemo-enzymatic approach for the asymmetric dearomatization of activated pyridines for the preparation of substituted piperidines with precise stereochemistry. The key step involves a stereoselective one-pot amine oxidase/ene imine reductase cascade to convert N-substituted tetrahydropyridines to stereo-defined 3- and 3,4-substituted piperidines. This chemo-enzymatic approach has proved useful for key transformations in the syntheses of antipsychotic drugs Preclamol and OSU-6162, as well as for the preparation of two important intermediates in synthetic routes of the ovarian cancer monotherapeutic Niraparib.

Synthesis of Nitrogen Heterocycles by a C–C Cross-Coupling/Cycloisomerization Strategy

AbstractThe present article presents a personalized Account on the synthesis of nitrogen heterocycles by combination of regioselective Pd-catalyzed cross-coupling reactions of polyhalogenated heterocycles, i.e., Suzuki–Miyaura and Sonogashira reactions, with acid-mediated cycloisomerization reactions. In many cases, the products constitute new heterocyclic core structures and show interesting optical and electronic properties.1 Introduction2 Acridines3 Phenathridines4 Azapyrenes5 Thienoquinolines6 Pyrrolonaphthyridines7 6-Aza-ullazines8 Conclusions

Synthesis of Nitrogen Heterocycles by Domino C–N Coupling/Hydroamination Reactions

AbstractThe present article presents a personalized Account on the synthesis of nitrogen heterocycles by domino C–N coupling/hydroamination reactions and related processes. The starting materials, 2-alkynyl-1-halohetarenes, are regioselectively available by Sonogashira reactions of various 1,2-dihalogenated heterocycles, such as thiophenes, benzothiophenes, furans and benzofurans, pyridines, quinolines, pyrimidines, and other ring systems. More complex products are formed by domino C–N coupling/hydroamination/C–H arylation reactions of 2-alkynyl-1-halohetarenes with 2-bromoanilines. In these reactions, not only two, but three bonds are formed in one step. In many cases, the products constitute new heterocyclic core structures and show interesting pharmacological or fluorescence properties.1 Introduction2 Domino C–N Coupling/Hydroamination Reactions3 Domino C–N Coupling/Hydroamination/C–H Arylation Reactions4 Conclusions

Copper-catalyzed [3+3] annulation of ketones with oxime acetates for the synthesis of pyridines.

A novel and efficient copper-catalyzed strategy for the synthesis of diverse pyridines through the [3+3] annulation of ketones with oxime acetates has been reported. It is very convenient to obtain various unsymmetrical 2,6-diarylpyridines by changing different substrates. The rare copper-catalyzed direct difunctionalization of saturated ketones for the synthesis of nitrogen heterocycles is developed. This protocol has excellent functional group tolerance, readily available raw materials, high chemoselectivity and broad substrate scope.

Progress in Synthesis of Nitrogen Heterocycles Catalyzed by Chiral Phosphine

Progress in Synthesis of Nitrogen Heterocycles Catalyzed by Chiral Phosphine

Recent advances in 3-aminoindazoles as versatile synthons for the synthesis of nitrogen heterocycles.

Nitrogen-based heterocycles are an important class of structural scaffolds distributed in biologically active natural products, medicinal chemistry, and agrochemicals. Hence, there is increasing interest in the development of novel synthetic strategies for the construction of these privileged structural motifs. Recently, 3-aminoindazoles have emerged as versatile synthons participating in a variety of condensation annulation, denitrogenative transannulation and rearrangement ring expansion reactions, which provide efficient synthetic routes for the formation of nitrogen heterocycles. This review systematically highlights for the first time the most recent advances in 3-aminoindazoles to provide a deep understanding of using 3-aminoindazoles as versatile synthons in organic transformations for synthetic and medicinal chemists.

Enhanced catalytic performance of ZnO/carbon materials in the green synthesis of poly-substituted quinolines

A highly efficient methodology for the selective synthesis of nitrogen heterocycles via Friedländer reaction using carbon materials supported ZnO catalysts under the green chemistry domain is presented. The influence of the physicochemical properties of different carbon supports, in particular an activated carbon (AC), multi-walled carbon nanotubes (MWCNT) and a carbon aerogel (CA), on the catalytic performance is discussed. The developed catalysts are easily prepared by simple incipient wetness impregnation and a subsequent thermal treatment. These ZnO/carbon catalysts showed a great performance in the Friedländer condensation of 2-amino-5-chlorobenzaldehyde and carbonylic compounds with enolizable hydrogens, under solvent-free and mild conditions, affording in all cases selectively a total conversion to the corresponding quinoline. Both the Zn loading in combination with the developed microporosity of the selected carbon supports seem to be the key factors determining the catalytic performance. Yields obtained with ZnO/carbon composites catalysts are superior to those obtained by others widely used in fine chemistry such as, Zn-catalysts supported on mesoporous silica (SBA-15) and Zn-metal-organic-frameworks (MOF).

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

Scandium(III)‐Triflate‐Catalyzed Multicomponent Reactions for the Synthesis of Nitrogen Heterocycles

AbstractThe need of understanding the interactions between small organic molecules and biological targets has stimulated the development of new methodologies for the synthesis of compounds with potential biological properties. In this scenario, multicomponent reactions have been considered as high atom‐efficient strategies which allow the generation of high levels of molecular diversity and complexity, using relatively simple and eco‐friendly experimental procedures. Among the plethora of catalysts used in multicomponent reactions, rare earth metal triflates, especially scandium(III) triflate [Sc(OTf)3], emerged as water‐resistant Lewis acids with remarkable catalytic activity in water‐containing environments. This review describes the recent progress on the use of scandium(III) triflate as Lewis acid catalyst for multicomponent reactions applied to the synthesis of nitrogen‐containing heterocycles, valuable privileged scaffolds in Organic and Medicinal Chemistry.