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The Chemistry of Imines

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Organic Chemistry".

Deadline for manuscript submissions: closed (31 January 2023) | Viewed by 38906

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Dr. Isabella Rimoldi

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Department of Pharmaceutical Science, University of Milan, Via Golgi 19, 20133 Milan, Italy
Interests: organometallic chemistry; asymmetric catalysis; hybrid catalysts; transition metal-based anticancer drugs
Special Issues, Collections and Topics in MDPI journals

Dr. Giorgio Facchetti

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Department of Pharmaceutical Science, University of Milan, Via Golgi 19, 20133 Milan, Italy
Interests: organometallic chemistry; catalysis; transition metal complexes; biological active molecules; asymmetric synthesis
Special Issues, Collections and Topics in MDPI journals

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Dear Colleagues,

Substituted imines are an important moiety present in a wide variety of natural molecules and synthetic analogues, displaying high biological activities as potent agents. Some of them are also used as ligands in coordinative organometallic complexes, playing a pivotal role in inducing activity at the metal center both for biological and catalytic applications. In the recent years, imine-ligand-containing metal complexes have attracted attention due to their ability to confer a luminescent behavior to the corresponding materials. Moreover, prochiral imines are often used as substrates for the synthesis of chiral amines that have pharmaceutical and industrial interest.

Considering the wide range of applications of imines, the aim of this Special Issue is to collect an overview of the chemistry of those used for different purposes both as ligands and precursors for the preparation of active molecules.

We are pleased to invite you to submit original research articles and reviews to contribute to this Special Issue.

We look forward to receiving your contributions.

Dr. Isabella Rimoldi
Dr. Giorgio Facchetti
Guest Editors

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Keywords

Schiff bases
amines
metal complexes
asymmetric reactions
alkaloids
luminescent materials

Published Papers (14 papers)

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12 pages, 2415 KiB

Open AccessArticle

An Innovative Structural Rearrangement in Imine Palladacycle Metaloligand Chemistry: From Single-Nuclear to Double-Nuclear Pseudo-Pentacoordinated Complexes

by Basma al Janabi, Francisco Reigosa, Gemma Alberdi, Juan M. Ortigueira and José M. Vila

Molecules 2023, 28(5), 2328; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28052328 - 02 Mar 2023

Cited by 1 | Viewed by 1255

Abstract

Treatment of the double nuclear complex 1a, di-μ-cloro-bis[N-(4-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph₂PCH₂CH₂)₂PPh (triphos) and NH₄PF₆ gave the single nuclear species 2a, 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate). Reaction of 2a with Ph₂PCH₂CH₂NH₂ in refluxing chloroform via a condensation reaction of the amine and formyl groups to produce the C=N double bond, gave 3a, 1-N-(cyclohexylamine)-4- N-(diphenylphosphinoethylamine)palladium(triphos)(hexafluorophasphate); a potentially bidentate [N,P] metaloligand. However, attempts to coordinate a second metal by treatment of 3a with [PdCl₂(PhCN)₂] were to no avail. Notwithstanding, complexes 2a and 3a left to stand in solution spontaneously self-transformed to give in either case the double nuclear complex 10, 1,4-N,N-terephthalylidene(cyclohexilamine)-3,6-[bispalladium(triphos)]di(hexafluorophosphate), after undergoing further metalation of the phenyl ring, then bearing two mutually trans [Pd(Ph₂PCH₂CH₂)₂PPh)-P,P,P] moieties: an unprecedented and serendipitous result indeed. On the other hand, reaction of the double nuclear complex 1b, di-μ-cloro-bis[N-(3-formylbenzylidene)cyclohexylaminato-C6, N]dipalladium, with Ph₂PCH₂CH₂)₂PPh (triphos) and NH₄PF₆ gave the single nuclear species 2b, 1-N-(cyclohexylamine)-4-N-(formyl)palladium(triphos)(hexafluorophasphate), Treatment of 2b with H₂O/glacial MeCOOH gave cleavage of the C=N double bond and of the Pd···N interaction, yielding 5b, isophthalaldehyde-6-palladium(triphos)hexafluorophosphate, which then reacted with Ph₂P(CH₂)₃NH₂ to yield complex 6b, N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)di(hexafluorophosphate), with two pairs of non-coordinated nitrogen and phosphorus donor atoms. Treatment of 6b with [PdCl₂(PhCN)₂], [PtCl₂(PhCN)₂], or [PtMe₂(COD)] gave the new double nuclear complexes 7b, 8b and 9b, palladiumdichloro-, platinumdichloro- and platinumdimethyl[N,N-(isophthalylidene(diphenylphosphinopropylamine)-6-(palladiumtriphos)(hexafluorophosphate)-P,P], respectively, showing the behavior of 6b as a palladated bidentate [P,P] metaloligand. The complexes were fully characterized by microanalysis, IR, ¹H, and ³¹P NMR spectroscopies, as appropriate. The X-ray single-crystal analyses for compounds 10 and 5b have been previously described as the perchlorate salts by JM Vila et al. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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13 pages, 968 KiB

Open AccessArticle

Chiral 8-Amino-5,6,7,8-tetrahydroquinoline Derivatives in Metal Catalysts for the Asymmetric Transfer Hydrogenation of 1-Aryl Substituted-3,4-dihydroisoquinolines as Alkaloids Precursors

by Giorgio Facchetti, Francesca Neva, Giulia Coffetti and Isabella Rimoldi

Molecules 2023, 28(4), 1907; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28041907 - 16 Feb 2023

Viewed by 1073

Abstract

Chiral diamines based on an 8-amino-5,6,7,8-tetrahydroquinoline backbone, known as CAMPY (L1), or the 2-methyl substituted analogue Me-CAMPY (L2) were employed as novel ligands in Cp* metal complexes for the ATH of a series of substituted dihydroisoquinolines (DHIQs), known for being key intermediates in the synthesis of biologically active alkaloids. Different metal-based complexes were evaluated in this kind of reaction, rhodium catalysts, C3 and C4, proving most effective both in terms of reactivity and enantioselectivity. Although modest enantiomeric excess values were obtained (up to 69% ee in the case of substrate I), a satisfactory quantitative conversion was successfully fulfilled even in the case of the most demanding hindered substrates when La(OTf)₃ was used as beneficial additive, opening up the possibility for a rational design of novel chiral catalysts alternatives to the Noyori-Ikariya (arene)Ru(II)/TsDPEN catalyst. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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17 pages, 1613 KiB

Open AccessArticle

2-Methyl-6-(4-aminophenyl)-4,5-dihydro-3(2H)-pyridazinone Synthon for Some New Annelated 1,2,3-Selena/Thiadiazoles and 2H-Diazaphospholes with Anticipated Biological Activity and Quantum Chemical Calculations

by I. E. El-Shamy, E. Hleli, M. A. El-Hashash, I. Kelnar and A. M. Abdel-Mohsen

Molecules 2023, 28(3), 1280; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28031280 - 28 Jan 2023

Cited by 1 | Viewed by 1561

Abstract

A convenient and efficient synthetic protocol for the new selenadiazole. Thiadiazole and diazaphosphole derivatives incorporating a pyridazine moiety originating from 4-(4-aminophenyl)-4-oxobutanoic acid (1) were described. All newly synthesized compounds were evaluated for their antimicrobial activity using the disk diffusion method, and their cytotoxicity was evaluated against brine shrimp lethality bioassay. Using density functional theory (DFT), the frontier molecular orbital (FMO) and molecular electrostatic potential (MEPS) were studied to estimate the chemical reactivity and kinetic stability of each structure. Therefore, global descriptor parameters like electronegativity (χ), chemical hardness (η), and global softness (σ) were calculated. Consequently, the attained results were compared with the experimental data of the biological activity of the studied structures. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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19 pages, 3222 KiB

Open AccessArticle

Aluminum Salen Complexes Modified with Unsaturated Alcohol: Synthesis, Characterization, and Their Activity towards Ring-Opening Polymerization of ε-Caprolactone and D,L-Lactide

by Kirill V. Zaitsev, Andrey D. Trubachev, Yuri F. Oprunenko, Yuliya A. Piskun, Irina V. Vasilenko, Andrei V. Churakov and Sergei V. Kostjuk

Molecules 2023, 28(3), 1262; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28031262 - 27 Jan 2023

Viewed by 1472

Abstract

A highly efficient one-step approach to the macromonomer synthesis using modified aluminum complexes as catalysts of ring-opening polymerization (ROP) of ε-caprolactone and D,L-lactide was developed. The syntheses, structures, and catalytic activities of a wide range of aluminum salen complexes, 3a-c, functionalized with unsaturated alcohol (HO(CH₂)₄OCH=CH₂) are reported. X-Ray diffraction studies revealed a tetragonal pyramidal structure for 3c. Among the complexes 3a-c, the highest activity in bulk ROP of ε-caprolactone and D,L-lactide was displayed by 3b, affording polyesters with controlled molecular weights at low monomer to initiator ratios (M_n up to 15,000 g mol⁻¹), relatively high polydispersities (Ð~1.8) and high number-average functionalities (F_n up to 85%). Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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12 pages, 4145 KiB

Open AccessArticle

Synthesis and Characterization of Novel Hydrazone Derivatives of Isonicotinic Hydrazide and Their Evaluation for Antibacterial and Cytotoxic Potential

by Muhammad Abdullah Shah, Ala Uddin, Muhammad Raza Shah, Imdad Ali, Riaz Ullah, Peer Abdul Hannan and Hidayat Hussain

Molecules 2022, 27(19), 6770; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27196770 - 10 Oct 2022

Cited by 12 | Viewed by 2426

Abstract

Hydrazones are active compounds having an azomethine –NHN=CH group and are widely studied owing to their ease of preparation and diverse pharmacological benefits. Novel isonicotinic hydrazone derivatives of vanillin aldehyde and salicyl aldehyde were synthesized that had azomethine linkages and were characterized by UV–Visible, FTIR, EI-MS, 1H-NMR and 13C-NMR spectroscopy. The compounds were screened for their antibacterial activity against Staphylococcus aureus, Bacillus subtilus, and Escherichia coli using disc diffusion and minimum inhibitory concentration (MIC) methods. For cytotoxicity, a brine shrimp lethality test was performed to calculate the lethal concentration (LC50). The results demonstrated appreciable antibacterial activities against the applied strains, amongst which the compounds coded NH3 and NH5 showed maximum inhibition and MIC responses. In terms of cytotoxic activity, the maximum effect was observed in compound NH5 and NH6 treatments with minimum survival percentages of 36.10 ± 3.45 and 32.44 ± 2.0, respectively. These hydrazones could be potential candidates in antitumorigenic therapy against various human cancer cells. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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17 pages, 2510 KiB

Open AccessArticle

Oxidation of Styrene to Benzaldehyde Catalyzed by Schiff Base Functionalized Triazolylidene Ni(II) Complexes

by Nasir S. Lawal, Halliru Ibrahim and Muhammad D. Bala

Molecules 2022, 27(15), 4941; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27154941 - 03 Aug 2022

Cited by 3 | Viewed by 1569

Abstract

Four new Schiff base functionalized 1,2,3-triazolylidene nickel complexes, [Ni-(L₁NHC)₂](PF₆)₂; 3, [Ni-(L₂NHC)₂](PF₆)₂; 4, [Ni-(L₃NHC)](PF₆)₂; 7 and [Ni-(L₄NHC)](PF₆)₂; 8, (where L₁NHC = (E)-3-methyl-1-propyl-4-(2-(((2-(pyridin-2-yl)ethyl)imino)methyl)phenyl)-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 1, L₂NHC = (E)-3-methyl-4-(2-((phenethylimino)methyl)phenyl)-1-propyl-1H-1,2,3-triazol-3-ium hexafluorophosphate(V), 2, L₃NHC = 4,4′-(((1E)-(ethane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 5, and L₄NHC = 4,4′-(((1E)-(butane-1,4-diylbis(azanylylidene))bis(methanylylidene))bis(2,1-phenylene))bis(3-methyl-1-propyl-1H-1,2,3-triazol-3-ium) hexafluorophosphate(V), 6), were synthesised and characterised by a variety of spectroscopic methods. Square planar geometry was proposed for all the nickel complexes. The catalytic potential of the complexes was explored in the oxidation of styrene to benzaldehyde, using hydrogen peroxide as a green oxidant in the presence of acetonitrile at 80 °C. All complexes showed good catalytic activity with high selectivity to benzaldehyde. Complex 3 gave a conversion of 88% and a selectivity of 70% to benzaldehyde in 6 h. However, complexes 4 and 7–8 gave lower conversions of 48–74% but with higher (up to 90%) selectivity to benzaldehyde. Results from kinetics studies determined the activation energy for the catalytic oxidation reaction as 65 ± 3 kJ/mol, first order in catalyst and fractional order in the oxidant. Results from UV-visible and CV studies of the catalytic activity of the Ni-triazolylidene complexes on styrene oxidation did not indicate any clear possibility of generation of a Ni(II) to Ni(III) catalytic cycle. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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15 pages, 5416 KiB

Open AccessArticle

Imine Palladacycles: Synthesis, Structural Analysis and Application in Suzuki–Miyaura Cross Coupling in Semi-Aqueous Media

by Brais Bermúdez-Puente, Luis A. Adrio, Fátima Lucio-Martínez, Francisco Reigosa, Juan M. Ortigueira and José M. Vila

Molecules 2022, 27(10), 3146; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27103146 - 14 May 2022

Cited by 2 | Viewed by 1786

Abstract

Treatment of the imines a–c with palladium(II) acetate in acetic acid yielded the μ-acetate dinuclear complexes 1a–c, which readily reacted with sodium chloride or bromide to provide μ-halide analogues. The reaction of the latter with nitrogen, phosphorus and oxygen donor nucleophiles yielded new imine palladacycles following the cleavage of the Pd₂X₂ unit. The complexes were fully characterized by microanalysis, ¹H, ¹³C and ³¹P NMR spectroscopies, as appropriate. The compounds were applied as catalysts in the Suzuki–Miyaura coupling reaction in aqueous and semi-aqueous media. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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18 pages, 4287 KiB

Open AccessArticle

Dicationic Bis-Pyridinium Hydrazone-Based Amphiphiles Encompassing Fluorinated Counteranions: Synthesis, Characterization, TGA-DSC, and DFT Investigations

by Ateyatallah Aljuhani, Nadjet Rezki, Salsabeel Al-Sodies, Mouslim Messali, Gamal M. S. ElShafei, Mohamed Hagar and Mohamed R. Aouad

Molecules 2022, 27(8), 2492; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27082492 - 12 Apr 2022

Cited by 4 | Viewed by 1460

Abstract

Quaternization and metathesis approaches were used to successfully design and synthesize the targeted dicationic bis-dipyridinium hydrazones carrying long alkyl side chain extending from C8 to C18 as countercation, and attracted to halide (I^-) or fluorinated ion (PF₆^-, BF₄^-, CF₃COO^-) as counteranion. Spectroscopic characterization using NMR and mass spectroscopy was used to establish the structures of the formed compounds. In addition, their thermal properties were investigated utilizing thermogravimetric analyses (TGA), and differential scanning calorimetry (DSC). The thermal study illustrated that regardless of the alkyl group length (Cn) or the attracted anions, the thermograms of the tested derivatives are composed of three stages. The mode of thermal decomposition demonstrates the important roles of both anion and alkyl chain length. Longer chain length results in greater van der Waals forces; meanwhile, with anions of low nucleophilicity, it could also decrease the intramolecular electrostatic interaction, which leads to an overall interaction decrease and lower thermal stability. The DFT theoretical calculations have been carried out to investigate the thermal stability in terms of the T_onset. The results revealed that the type of the counteranion and chain length had a substantial impact on thermal stability, which was presumably related to the degree of intermolecular interactions. However, the DFT results illustrated that there is no dominant parameter affecting the thermal stability, but rather a cumulative effect of many factors of different extents. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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18 pages, 2132 KiB

Open AccessArticle

Design, Synthesis and Bioactivity Evaluation of Coumarin–BMT Hybrids as New Acetylcholinesterase Inhibitors

by Fanxin Zeng, Tao Lu, Jie Wang, Xuliang Nie, Wanming Xiong, Zhongping Yin and Dayong Peng

Molecules 2022, 27(7), 2142; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27072142 - 26 Mar 2022

Cited by 3 | Viewed by 2089

Abstract

Coumarin possesses the aromatic group and showed plentiful activities, such as antioxidant, preventing asthma and antisepsis. In addition, coumarin derivatives usually possess good solubility, low cytotoxicity and excellent cell permeability. In our study, we synthesized the compound bridge methylene tacrine (BMT), which has the classical pharmacophore structure of Tacrine (THA). Based on the principle of active substructure splicing, BMT was used as a lead compound and synthesized coumarin–BMT hybrids by introducing coumarin to BMT. In this work, 21 novel hybrids of BMT and coumarin were synthesized and evaluated for their inhibitory activity on AChE. All obtained compounds present preferable inhibition. Compound 8b was the most active compound, with the value of K_i as 49.2 nM, which was higher than Galantamine (GAL) and lower than THA. The result of molecular docking showed that the highest binding free energy was −40.43 kcal/mol for compound 8b, which was an identical trend with the calculated K_i. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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16 pages, 22884 KiB

Open AccessArticle

Potential COVID-19 Drug Candidates Based on Diazinyl-Thiazol-Imine Moieties: Synthesis and Greener Pastures Biological Study

by Sraa Abu-Melha, Mastoura Mohamed Edrees, Musa A. Said, Sayed M. Riyadh, Nadia S. Al-Kaff and Sobhi M. Gomha

Molecules 2022, 27(2), 488; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27020488 - 13 Jan 2022

Cited by 12 | Viewed by 2177

Abstract

A novel series of 1-aryl-N-[4-phenyl-5-(arylazo)thiazol-2-yl)methanimines has been synthesized via the condensation of 2-amino-4-phenyl-5-arylazothiazole with various aromatic aldehydes. The synthesized imines were characterized by spectroscopic techniques, namely ¹H and ¹³C-NMR, FTIR, MS, and Elemental Analysis. A molecular comparative docking study for 3a–f was calculated, with reference to two approved drugs, Molnupiravir and Remdesivir, using 7BQY (M^pro; PDB code 7BQY; resolution: 1.7 A°) under identical conditions. The binding scores against 7BQY were in the range of −7.7 to −8.7 kcal/mol for 3a–f. The high scores of the compounds indicated an enhanced binding affinity of the molecules to the receptor. This is due to the hydrophobic interactions and multi-hydrogen bonds between 3a–f ligands and the receptor’s active amino acid residues. The main aim of using in silco molecular docking was to rank 3a–f with respect to the approved drugs, Molnupiravir and Remdesivir, using free energy methods as greener pastures. A further interesting comparison presented the laydown of the ligands before and after molecular docking. These results and other supporting statistical analyses suggested that ligands 3a–f deserve further investigation in the context of potential therapeutic agents for COVID-19. Free-cost, PASS, SwissADME, and Way2drug were used in this research paper to determine the possible biological activities and cytotoxicity of 3a–f. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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25 pages, 35336 KiB

Open AccessArticle

Synthesis, Structural Characterization, and In Vitro and In Silico Antifungal Evaluation of Azo-Azomethine Pyrazoles (PhN₂(PhOH)CHN(C₃N₂(CH₃)₃)PhR, R = H or NO₂)

by Dorancelly Fernandez, Andrés Restrepo-Acevedo, Cristian Rocha-Roa, Ronan Le Lagadec, Rodrigo Abonia, Susana A. Zacchino, Jovanny A. Gómez Castaño and Fernando Cuenú-Cabezas

Molecules 2021, 26(24), 7435; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules26247435 - 08 Dec 2021

Cited by 6 | Viewed by 2751

Abstract

The azo-azomethine imines, R¹-N=N-R²-CH=N-R³, are a class of active pharmacological ligands that have been prominent antifungal, antibacterial, and antitumor agents. In this study, four new azo-azomethines, R¹ = Ph, R² = phenol, and R³ = pyrazol-Ph-R’ (R = H or NO₂), have been synthesized, structurally characterized using X-ray, IR, NMR and UV–Vis techniques, and their antifungal activity evaluated against certified strains of Candida albicans and Cryptococcus neoformans. The antifungal tests revealed a high to moderate inhibitory activity towards both strains, which is regulated as a function of both the presence and the location of the nitro group in the aromatic ring of the series. These biological assays were further complemented with molecular docking studies against three different molecular targets from each fungus strain. Molecular dynamics simulations and binding free energy calculations were performed on the two best molecular docking results for each fungus strain. Better affinity for active sites for nitro compounds at the “meta” and “para” positions was found, making them promising building blocks for the development of new Schiff bases with high antifungal activity. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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Review

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27 pages, 4929 KiB

Open AccessReview

Asymmetric Reactions of N-Phosphonyl/Phosphoryl Imines

by Devalina Ray, Suman Majee, Ram Naresh Yadav and Bimal Krishna Banik

Molecules 2023, 28(8), 3524; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules28083524 - 17 Apr 2023

Cited by 3 | Viewed by 1357

Abstract

The asymmetric reactions of imines continued to attract the attention of the scientific community for decades. However, the stereoselective reactions of N-phosphonyl/phosphoryl imines remained less explored as compared to other N-substituted imines. The chiral auxiliary-based asymmetric-induction strategy with N-phosphonyl imines could effectively generate enantio- and diastereomeric amine, α,β-diamine, and other products through various reactions. On the other hand, the asymmetric approach for the generation of chirality through the utilization of optically active ligands, along with metal catalysts, could be successfully implemented on N-phosphonyl/phosphoryl imines to access numerous synthetically challenging chiral amine scaffolds. The current review critically summarizes and reveals the literature precedence of more than a decade to highlight the major achievements existing to date that can display a clear picture of advancement as well drawbacks in this area. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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51 pages, 15589 KiB

Open AccessReview

Diaza-1,3-butadienes as Useful Intermediate in Heterocycles Synthesis

by Jorge Heredia-Moya, Daniel A. Zurita, José Eduardo Cadena-Cruz and Christian D. Alcívar-León

Molecules 2022, 27(19), 6708; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27196708 - 09 Oct 2022

Cited by 3 | Viewed by 2907

Abstract

Many heterocyclic compounds can be synthetized using diaza-1,3-butadienes (DADs) as key structural precursors. Isolated and in situ diaza-1,3-butadienes, produced from their respective precursors (typically imines and hydrazones) under a variety of conditions, can both react with a wide range of substrates in many kinds of reactions. Most of these reactions discussed here include nucleophilic additions, Michael-type reactions, cycloadditions, Diels–Alder, inverse electron demand Diels–Alder, and aza-Diels–Alder reactions. This review focuses on the reports during the last 10 years employing 1,2-diaza-, 1,3-diaza-, 2,3-diaza-, and 1,4-diaza-1,3-butadienes as intermediates to synthesize heterocycles such as indole, pyrazole, 1,2,3-triazole, imidazoline, pyrimidinone, pyrazoline, -lactam, and imidazolidine, among others. Fused heterocycles, such as quinazoline, isoquinoline, and dihydroquinoxaline derivatives, are also included in the review. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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24 pages, 6868 KiB

Open AccessReview

Different Schiff Bases—Structure, Importance and Classification

by Edyta Raczuk, Barbara Dmochowska, Justyna Samaszko-Fiertek and Janusz Madaj

Molecules 2022, 27(3), 787; https://0-doi-org.brum.beds.ac.uk/10.3390/molecules27030787 - 25 Jan 2022

Cited by 91 | Viewed by 13183

Abstract

Schiff bases are a vast group of compounds characterized by the presence of a double bond linking carbon and nitrogen atoms, the versatility of which is generated in the many ways to combine a variety of alkyl or aryl substituents. Compounds of this type are both found in nature and synthesized in the laboratory. For years, Schiff bases have been greatly inspiring to many chemists and biochemists. In this article, we attempt to present a new take on this group of compounds, underlining of the importance of various types of Schiff bases. Among the different types of compounds that can be classified as Schiff bases, we chose hydrazides, dihydrazides, hydrazones and mixed derivatives such as hydrazide–hydrazones. For these compounds, we presented the elements of their structure that allow them to be classified as Schiff bases. While hydrazones are typical examples of Schiff bases, including hydrazides among them may be surprising for some. In their case, this is possible due to the amide-iminol tautomerism. The carbon–nitrogen double bond present in the iminol tautomer is a typical element found in Schiff bases. In addition to the characteristics of the structure of these selected derivatives, and sometimes their classification, we presented selected literature items which, in our opinion, represent their importance in various fields well. Full article

(This article belongs to the Special Issue The Chemistry of Imines)

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