Aromatic Imines Research Articles

Electrocatalytic Hydrogenation and Deuteration of Unsaturated C-N Bonds to Amines with Vacancy-rich Cu3P Nanowires as Catalysts in Aqueous Solution.

Renewable energy driven electrochemically hydrogenation of unsaturated C-N bonds with water as a hydrogen source provides an eco-friendly route for amine production. However, the potential commercial applications of this strategy were limited by the lack of relevant extended research. Here we demonstrate an efficient electrochemical hydrogenation system for the formation of amines from nitriles by a vacancy-rich copper phosphide catalyst. The catalytic system achieves a yield of 99% and a Faraday efficiency of 99% for the hydrogenation of benzonitrile. Mechanism study shows that benzonitrile is spontaneously adsorbed on the electrode surface and the electrogenerated active adsorbed hydrogen is the key reactive intermediate for hydrogenation. Theoretical calculation results show that vacancy-induced active sites chemisorb the N atom, thus accelerating C≡N bond activation for hydrogenation. Encouragingly, good yields of amines (≥99%) are obtained when benzonitrile is replaced by a series of aromatic nitriles, heterocyclic nitriles, aliphatic nitriles, and imines. These results show the general applicability of this method for the synthesis of various amines.

Copper(II) triflate-mediated addition reaction of 2-tributylstannyl-1,3-dithiane with imines

Abstract The addition of 2-tributylstannyl-1,3-dithiane to imines was achieved using copper(II) triflate in MeNO2 at room temperature. Furthermore, this reaction can be applied to various aromatic and heteroaromatic imines. Consequently, the corresponding α-amino-1,3-dithiane derivatives were efficiently and readily synthesized under mild conditions.

Air-Stable Iron(III) Salen Complexes for Selective Hydroboration of Ketones and Unactivated Imines without Base Activation.

Herein, we designed and synthesized a series of air-stable, cost-effective, and readily synthesizable iron(III) salen complexes (Fe-1 and Fe-2) for facilitating the selective hydroboration of ketones and unactivated imines with pinacolborane in the absence of any additive. These catalyst systems exhibited good yields, chemoselectivity, high atom economy, and a broad substrate scope under mild reaction conditions with a minimal catalyst loading of 0.2 mol %. The catalytic efficiency of Fe-1 has been demonstrated through the hydroboration of diverse aromatic, aliphatic, and heterocyclic ketones and imines with a turnover number of up to 1000, highlighting its broad substrate scope. Ketones are chemoselectively hydroborated over other functional groups such as imines, alkenes, esters, nitriles, acids, and alcohols. Besides, the synthetic utility of this strategy has also been showcased by the construction of a natural chiral monoterpenoid carveol. This protocol can be readily scaled up for gram-scale synthesis of alcohols, which underscores the potential industrial applicability of our catalyst system in the synthesis of secondary alcohols on a larger scale.

Novel Yellow Aromatic Imine Derivative Incorporating Oxazolone Moiety for Color Resist Applications

A novel aromatic imine derivative, 2′-(1,4-phenylene)bis[4-[(4-methoxyphenyl)methylene]-5(4H)-oxazolone] (PBMBO), was designed and synthesized as a yellow colorant additive for green color filters used in image sensors. The optical and thermal properties of the newly developed material were evaluated both in solution and within color filter film conditions. PBMBO demonstrated a molar extinction coefficient of 2.24 × 104 L/mol·cm in solution, surpassing that of the commercially employed yellow colorant MBIQO by a factor of 1.82. Color resist (CR) films incorporating PBMBO exhibited outstanding optical characteristics, displaying 0.03% transmittance at 435 nm, 99.3% transmittance at 530 nm, and a sharp slope within the 400 to 550 nm range. The decomposition temperature of PBMBO was 303 °C, indicating relatively superior thermal stability compared to MBIQO. Consequently, PBMBO emerges as a highly promising candidate for a yellow colorant additive in imaging sensor color filters, owing to its exceptional optical and thermal stability. Its potential applications are anticipated to extend across various fields of organic semiconductors.

Cyanomethylation of imines enabled by a mild deprotonation of acetonitrile using a combination of TMSCF3 and CsF

β-Amino acids are important structural units in chemistry and biology. Herein we reported a method to synthesize β-amino nitriles, the crucial synthetic precursor to β-amino acids. By using a nucleophilic base-complex, in situ generated from TMSCF3 and CsF, addition of acetonitrile to a series of aromatic imines offered the corresponding β-amino nitriles in excellent yields. Moreover, other electron withdrawing group bearing methyl group could be deprotonated to produce a good nucleophile under this mild conditions.

Oxidative Control of Photoinduced Cascade Electrocyclizations in Aromatic Azido Imines to Access Complex Fused Imidazoles or Pyrazoles.

Photoinduced cascade of two 6π-electron six- and five-center electrocyclizations in aromatic azido imines is oxidatively controlled to yield complex fused benzimidazoles or indazoles. Formation of benzimidazoles occurs via an unprecedented carbon-to-nitrogen o-iminoaryl 1,2-shift.

Synthesis and Crystal Structure Analysis of Some Aromatic Imines of Syringaldehyde

A series of syringaldehyde imines with para-substituted anilines have been synthesized in a good yield, and their crystal structures have been analyzed. The orientation of the syringaldehyde hydroxyl group plays in important role in the intermolecular hydrogen-bonding pattern of the molecules. The O–H…N hydrogen bonding interactions primarily determine the three-dimensional packing of the molecules, even though they make up a relatively small percentage of intermolecular interactions in the molecules. The three structures with the p-hydroxy group cis to the imine group give hydrogen-bonded zigzag chains in the monoclinic crystals, while the structure with a trans hydroxy group crystallize in a hexagonal space group (R3¯) and form hydrogen-bonded hexamers. The hexagonal structure also displays Br…Br interactions, forming additional hexameric clusters. The analysis of published p-hydroxyphenyl imine crystal structures from the Cambridge Crystallographic Database revealed patterns in the length of the hydrogen bonding interactions based on steric congestion around the hydroxyl group.

Asymmetric aza-Henry reaction of BOC-protected imines with zinc-FAM catalyst

Derivatives of ferrocenyl-substituted aziridinyl methanol (FAM) ligands were used with zinc metal for asymmetric aza-Henry (nitro-aldol) reaction of N-Boc protected imines with nitroalkanes. At optimized reaction conditions Zn-PFAM1 catalyst system with a variety of aromatic imines provided products in up to 77% ee and 88% yield. In addition, the reaction of N-Boc substituted imines with nitroethane also proceeded smoothly with moderate enantioselectivities and diastereoselectivities.

Enantioselective dearomative formal (3+3) cycloadditions of bicyclobutanes with aromatic azomethine imines: access to fused 2,3-diazabicyclo[3.1.1]heptanes.

Although cycloadditions of bicyclobutanes (BCBs) have emerged as a reliable approach for producing bicyclo[n.1.1]alkanes such as azabicyclo[3.1.1]heptanes (aza-BCHeps), serving as saturated bioisosteres of arenes, the catalytic asymmetric variant remains underdeveloped and presents challenges. Herein, we developed several Lewis acid-catalyzed systems for the challenging dearomative (3+3) cycloaddition of BCBs and aromatic azomethine imines. This resulted in fused 2,3-diazabicyclo[3.1.1]heptanes, introducing a novel chemical space for the caged hydrocarbons. Moreover, an asymmetric Lewis acid catalysis strategy was devised for the (3+3) cycloadditions of BCBs and N-iminoisoquinolinium ylides, forming chiral diaza-BCHeps with up to 99% yield and 97% ee. This study showcases a unique instance of asymmetric (3+3) cycloaddition facilitated by the creation of a chiral environment via the activation of BCBs.

Molecular Docking, Synthesis and Antimicrobial Evaluation of 4-[(3 hydroxybenzalidene)amino]antipyrine and its Copper Complex

The synthesis and characterization of Schiff base-containing transition metal complexes have gained increasing importance due to their catalytic roles in various reactions and their biological activities. These metal complexes have become crucial in drug design, leading to a growing interest in metal-based drugs. The study aimed to synthesize copper metal complex with a new Schiff base ligand 4-[(3-hydroxybenzalidene)amino]antipyrine derived from 4-aminoantipyrine and 3-hydroxybenzaldehyde, as well as evaluate their antimicrobial activity against gram positive and gram-negative bacterial strains. The ligand and its copper complex were assessed for antimicrobial activity against gram-positive and gram-negative strains utilizing disc diffusion and broth dilution methods. Spectroscopic techniques (UV-Vis, FT-IR, XRD, and EDXRF), solubility tests, and elemental analysis were employed to investigate the ligand and copper complex. The ligand displayed high insolubility in various solvents but had limited solubility in chloroform and methyl chloride. The FTIR spectrum of the Schiff base reveals the presence of aromatic hydrocarbons, imine (C=N), hydroxyl (-OH), secondary amine (C-N), carbonyl (C=O), and vibrations associated with C-O and C-C bonds, reflecting its molecular structure. In the EDXRF analysis, a prominent peak at 7.80 keV corresponding to copper was detected, indicating that copper is the most abundant element found in the ligand. XRD analysis demonstrated distinct crystal structures for both the ligand and its copper complex. The UV-Vis spectra of the ligand exhibited an absorption peak at a UV lambda max of 220 nm, indicating a π→π* transition. In contrast, the absorption peaks observed in the copper complex indicated different transitions compared to the Schiff base. The MIC results indicated the copper complex's stronger antimicrobial activity than the Schiff base against tested bacteria. Molecular docking studies showed that the interaction energies of the synthesized compounds, particularly the ligand and copper complex, surpassed that of the well-known anti-diabetic drug, metformin.

Camphor Sulfonimine Compounds: Bottom-up Design of MOFs from Organic Frameworks Based on X-rays and DFT-D3

DFT-D3 calculations based on structural X-ray diffraction data obtained for 3-oxo-camphorsulfonyl imine (1), camphorsulfonyl chloride (2) and seven camphor sulfonimines (O2SNC10H13NR, L1−L7), from which L2 (R=4-OHC6H4), L4 (R=4-ClC6H4) and L6 (R=3,5-(CH3)2C6H3) are synthesized and characterized in this work, provide information into the intra- and inter-molecular interactions with concomitant elucidation of the supramolecular arrangement of the compounds. The DFT‑D3 calculations performed in small clusters of two or three molecular units reproduce the interactions observed via X-ray analyses, showing that, as a general trend, the structural arrangement of the molecules is driven by electronic rather than by packing parameters. In all compounds, the self-assembly of 3D structures involves the sulfonyl imine group (‑NSO2) either to establish hydrogen bonds through oxygen atoms or non-classic oxygen–aliphatic hydrogen or non-bonding interactions (NBIs), which also involve sulfonyl oxygen atoms. Interestingly, the camphor sulfonimine compounds (L2, L3), having protic groups (R=C6H4X:X=OH, L2 or X=NH2, L3) at the aromatic imine substituents (=NR), present an extra π-π stacking, which is absent in the other compounds’ aromatic derivatives. The X-ray analysis shows that all the reported camphor sulfonimine compounds display the E configuration with respect to the imine substituent (R). The study of the redox behavior of the compounds by cyclic voltammetry enables insight into the solution properties of the compounds and the rationalization of the molecular interactions that stand in the solid and solution states. Camphor sulfonimine compounds (L) display appropriate binding atoms to coordinate transition metals. The results herein show that monodentate coordination through the nitrogen atom of the sulfonimine five-membered ring to the {Ag(NO3)} metal center is favored. When this imine nitrogen atom is not itself involved in the organic framework, DFT-D3 calculations show that the complexation does not affect the non-covalent interactions that are reproduced in the MOF structure.

Ultrahigh tough, self-healing copolymer elastomer crosslinked by reversible imine system

Improvement of toughness is still a challenge for self-healing materials. Most of self-healing materials difficultly balance the mechanical and self-healing property. Here, a molecular design strategy of copolymer is proposed based on three combinations of reversible imine bond, chain motion and thermosensitive hydrogen bond together. The approach initially forms a co-continuous microphase separation structure and then cross-linked by aromatic imine via esterification reaction and Schiff base reaction, which features efficient self-healing, ultrahigh strength and toughness. The resultant elastomer exhibits a high stress at break (≈3 MPa) and high fracture strain (≈600 %). Additionally, the elastomer can reach 95 % self-healing efficiency after healing at 100 °C for 12 h. Extra reversible imine crosslinking displays a doubly promotion for fracture stress, and unchanging strain as well as 1times increase for self-healing efficiency, compared with merely chain motion and hydrogen bonding. This elastomer can be successfully spun into stretchable, conductive, self-healing filaments with core-shell structure by wet spinning and coating methods. It shows excellent corrosion resistance against NaCl, and conductive and self-healing property after coating by PANI polymer. This new type of self-healing polymer is promising to expand the application in future tissue engineering, soft robotics, and biomedical devices.

Internal hydrogen bonding of imines to control and enhance the dynamic mechanical properties of covalent adaptable networks

Covalent Adaptable Networks (CANs) have the potential to replace current thermoset materials, as the dynamic covalent bonds in CANs enable reprocessability and recycling of crosslinked polymer networks. A current limitation of CANs is, however, that they are generally susceptible towards creep, as the bond exchange reactions facilitate stress relaxation. In this work, we propose the use of internal hydrogen bonding in polyimine CANs as an efficient tool to enhance creep resistance (at operating temperature) and further control the dynamic mechanical properties, while still enabling malleability at elevated temperatures. We are able to show on a small-molecule level that ortho-substituted hydroxy groups on aromatic imines stabilise the dynamic covalent imine bonds as a result of the internal hydrogen bond that is formed between the hydroxy and imine group. Furthermore, we show that polyimine CANs with incorporated ortho hydroxy groups have significantly enhanced material properties, as can be seen in the glass transition temperature (Tg), elastic modulus (G’), creep resistance and solvent resistance. While we also consider additional steric and electronic effects that might have arisen due to installation of the hydroxy groups, we find that the stabilising effect of the internal hydrogen bond is primarily dictating the material performance.

Palladium‐Catalyzed Regioselective peri‐ and ortho‐Halogenation of 1‐Naphthaldehydes: Application to the Synthesis of Polycyclic Natural Product Skeletons

AbstractHerein, a regioselective bromination or chlorination reaction of 1‐naphthaldehydes is described. Without additive, the palladium‐catalyzed C−H halogenation showed a C8‐regioselectivity, whereas the formation of an aromatic imine intermediate allowed a switch to a C2‐reactivity. Mechanistic studies and DFT calculations were performed to explain the regioselectivity and the synthesized halogenated products were used as key building blocks to access polycyclic natural product skeletons.

Designed synthetic pathway of stereoselective novel monocyclic cis‐bis‐β‐lactams including a 1,3,4‐thiadiazole‐2,5‐dithiol constituent: Antimicrobial activity, molecular docking

AbstractA simple synthetic method has been developed for novel monocyclic bis‐β‐lactams including a 1,3,4‐thiadiazole‐2,5‐thiol constituent via [2 + 2] cycloaddition reactions, that is, Staudinger reaction (ketene‐imine) of acyl chloride and numerous aromatic imines. Easily available starting materials, an easy workup, a simple purification process, no column chromatography needed, and a great yield are specific features of this work. Spectroscopic methods revealed the confirmation of synthesized products. Products were easily purified through a simple crystallization technique. The stereochemistry of bis‐β‐lactam derivatives at C‐3 and C‐4 stereocenters was validated by 1H NMR spectra. All synthesized products exhibited good antimicrobial activities against three Gram‐positive bacteria Staphylococcus aureus, Bacillus anthracis, and Clostridium perfringens, and two Gram‐negative bacteria Escherichia coli, Brucella abortus. The molecular docking studies were carried out with the target receptor from E. coli, S. aureus, B. anthracis, B. abortus, and C. perfringens of PDB ID: 3T88, 4Q7G, 3Q2O, 4WJM, and 6PV4, respectively, to obtain a moderate binding interaction.

A novel aromatic imine-containing DOPO-based reactive flame retardant towards enhanced flame-retardant and mechanical properties of epoxy resin

For improving the flame-retardant performance of epoxy thermosets without sacrificing other properties, a novel aromatic imine-containing DOPO-based bisphenol, DOPO-AI, was synthesized. Diglycidyl ether bisphenol F epoxy resin (DGEBF) reacted with DOPO-AI first, followed by curing with 4, 4′-diaminodiphenylmethane (DDM). When the mass of DOPO-AI was 25% of DGEBF, the resulting epoxy thermoset EP/20DOPO-AI exhibited the V-0 rating with the limiting oxygen index of 35.4%. In the cone calorimetry test, the peak heat release rate and total heat release of EP/20DOPO-AI showed the reduction of 26% and 27%, respectively, compared to those of DGEBF/DDM (EP). The mechanism of DOPO-AI in reducing heat release and increasing char-form ability of EP/DOPO-AI was studied. Interestingly, the mechanical and thermal mechanical properties of EP/20DOPO-AI were improved, although the crosslinking density was much lower than that of EP. The tensile strength and storage modulus of EP/20DOPO-AI were increased by 13% and 5%, while the glass transition temperature and the elongation at break were kept, compared with those of EP. The high rigidity of DOPO and aromatic imine was the reason for the improvement of the mechanical properties of EP/20DOPO-AI. Furthermore, EP/20DOPO-AI showed a small reduction in thermal stability, compared with that of EP.

Reductive photoredox transformations of carbonyl derivatives enabled by strongly reducing photosensitizers.

Visible-light photoredox catalysis is well-established as a powerful and versatile organic synthesis strategy. However, some substrate classes, despite being attractive precursors, are recalcitrant to single-electron redox chemistry and thus not very amenable to photoredox approaches. Among these are carbonyl derivatives, e.g. ketones, aldehydes, and imines, which in most cases require Lewis or Brønsted acidic additives to activate via photoinduced electron transfer. In this work, we unveil a range of photoredox transformations on ketones and imines, enabled by strongly reducing photosensitizers and operating under simple, general conditions with a single sacrificial reductant and no additives. Specific reactions described here are umpolung C-C bond forming reactions between aromatic ketones or imines and electron-poor alkenes, imino-pinacol homocoupling reactions of challenging alkyl-aryl imine substrates, and γ-lactonization reactions of aromatic ketones with methyl acrylate. The reactions are all initiated by photoinduced electron transfer to form a ketyl or iminyl that is subsequently trapped.

Effects of Through-Bond and Through-Space Conjugations on the Photoluminescence of Small Aromatic and Aliphatic Aldimines.

Through-bond conjugation (TBC) and/or through-space conjugation (TSC) determine the photophysical properties of organic luminescent compounds. No systematic studies have been carried out to understand the transition from aromatic TBC to non-aromatic TSC on the photoluminescence of organic luminescent compounds. In this work, a series of small aromatic and aliphatic aldimines were synthesized. For the aromatic imines, surprisingly, N,1-diphenylmethanimine with the highest TBC is non-emissive, while N-benzyl-1-phenylmethanimine and N-cyclohexyl-1-phenylmethanimine emit bright fluorescence in aggregate states. The aliphatic imines are all emissive, and their maximum emission wavelength decreases while the quantum yield increases with a decrease in steric hindrance. The imines show concentration-dependent and excitation-dependent emissions. Theoretical calculations show that the TBC extents in the aromatic imines are not strong enough to induce photoluminescence in a single molecule state, while the intermolecular TSC becomes dominant for the fluorescence emissions of both aromatic and aliphatic imines in aggregate states, and the configurations and spatial conformations of the molecules in aggregate states play a key role in the formation of effective TSC. This study provides an understanding of how chemical and spatial structures affect the formation of TBC and TSC and their functions on the photoluminescence of organic luminescent materials.

Interlocked Covalent Adaptable Networks and Composites Relying on Parallel Connection of Aromatic Disulfide and Aromatic Imine Cross-Links in Epoxy

Covalent adaptable networks (CANs) relying on dynamic cross-links have been developed to make the cross-linked polymeric materials and composites degradable. However, due to the reversibility of dynamic bonds, the CANs and composites suffer accidental degradation and failure upon a certain stimulus (moisture, acid/base, reductant/oxidant, etc.) in the application environment. Herein, inspired by parallel circuits, interlocked covalent adaptable networks (ICANs) were prepared by one-pot reactions from epoxy monomers and two curing agents that contained different dynamic bonds of aromatic disulfide and aromatic imine bonds, resulting in dual dynamic parallel cross-links in homogeneous epoxy networks. The ICANs exhibited outstanding mechanical properties and improved stability, relying on the topological interlocking structure. The ICANs could be unlocked and became degradable only when two stimuli were both applied to completely break the cross-links of disulfide bonds and imine bonds. When applying ICANs as a matrix to form carbon fiber-reinforced polymer (CFRP) composites, the resulted CFRP inherited the interlocking properties from the ICANs, exhibiting improved stability and nondestructive recyclability. Maintaining the degradable properties, the interlocking structure of networks provided a facile way to optimize the stability of CANs and their composites.

Synthesis and Flame-Retardant Performance of Epoxy Resins Containing Aromatic Imine from Different Bisphenols Based on the Duff Reaction

Synthesis and Flame-Retardant Performance of Epoxy Resins Containing Aromatic Imine from Different Bisphenols Based on the Duff Reaction