Bearing Electron Withdrawing Groups Research Articles

Organic Donor-Acceptor Thermally Activated Delayed Fluorescence Photocatalysts in the Photoinduced Dehalogenation of Aryl Halides.

We report a family of donor-acceptor thermally activated delayed fluorescent (TADF) compounds based on derivatives of DMAC-TRZ, that are strongly photoreducing. Both Eox and thus E*ox could be tuned via substitution of the DMAC donor with a Hammett series of p-substituted phenyl moieties while Ered remained effectively constant. These compounds were assessed in the photoinduced dehalogenation of aryl halides, and analogues bearing electron withdrawing groups were found to produce the highest yields. Substrates of up to Ered=-2.72 V could be dehalogenated at low PC loading (1 mol %) and under air, conditions much milder than previously reported for this reaction. Spectroscopic and chemical studies demonstrate that all PCs, including literature reference PCs, photodegrade, and that it is these photodegradation products that are responsible for the reactivity.

Organic Donor–Acceptor Thermally Activated Delayed Fluorescence Photocatalysts in the Photoinduced Dehalogenation of Aryl Halides

AbstractWe report a family of donor‐acceptor thermally activated delayed fluorescent (TADF) compounds based on derivatives of DMAC‐TRZ, that are strongly photoreducing. Both Eox and thus E*ox could be tuned via substitution of the DMAC donor with a Hammett series of p‐substituted phenyl moieties while Ered remained effectively constant. These compounds were assessed in the photoinduced dehalogenation of aryl halides, and analogues bearing electron withdrawing groups were found to produce the highest yields. Substrates of up to Ered=−2.72 V could be dehalogenated at low PC loading (1 mol %) and under air, conditions much milder than previously reported for this reaction. Spectroscopic and chemical studies demonstrate that all PCs, including literature reference PCs, photodegrade, and that it is these photodegradation products that are responsible for the reactivity.

Synthesis, molecular docking and pharmacological evaluations of novel naphthalene-pyrazoline hybrids as new orally active anti-inflammatory agents

The pyrazoline nucleus is widely present in diverse compounds as it serves as a valuable template for the discovery of new class of bioactive compounds. Various substituted 2-pyrazolines exhibit a spectrum of pharmacological activities, including antimicrobial, anti-inflammatory, analgesic, and antitumor properties. In view of this, we have synthesized a novel class of naphthalene-pyrazoline hybrids (PY1-PY20). All the synthesized hybrids were thoroughly characterized by means of standard spectroscopic techniques and tested for their in-vivo anti-inflammatory activity. Most of the compounds exhibited significant anti-inflammatory activity and in particular the compounds bearing electron withdrawing groups had potential in vivo activity. Further, in-silico molecular docking studies were carried out using the ‘Molegro Virtual Docker’ as a docking tool against the target proteins such as COX-1 (PDB ID: 1EQH) and COX-2 (PDB ID: 1PXX). The results revealed that the majority of pyrazolines form hydrogen interactions with key residues (Ser 530, Tyr 385, Tyr 355, Arg 120, Ser 353, Arg 83) in the active binding sites of COX-1 (1EQH) and COX-2 (1PXX). Notably, interactions with residues Tyr 355, Arg 120, Ser 530 for COX-1, and Tyr 355, Arg 120, Gln 192, Leu 352, Ser 353, His 90, Tyr 38, Ser 530, and Tyr 385 for COX-2 are crucial for the reported anti-inflammatory activity of diverse compounds. Ligand-protein inverse molecular docking studies highlight specific hydrogen bond interactions, with PY-8, PY-11, PY-15, and PY-17 showing significant interactions. The study was able to identify potential anti-inflammatory naphthalene-pyrazoline derivatives.

In vitro and in silico correlation of benzoxazole-based thiazolidinone hybrids derivatives: A promising acetylcholinesterase and butyrylcholinesterase inhibitors

Benzoxazole-based thiazolidinone hybrids derivatives (1–19) were afforded and further subjected to in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibition studies for the first time. All these analogues were found to display good inhibition against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE)enzymes with IC50 values 4.20 ± 1.10 µM to 43.20 ± 4.50 µM (against AChE) and 3.80 ± 1.20 µM to 34.50 ± 3.30 µM (against BuChE) as compared to standard donepezil having IC50 values of 21.86 ± 0.40 µM (against AChE) and 32.47 ± 2.30 µM (against BuChE) respectively. Specifically, compound 16, characterized by a 3,4-dichloro substitution on ring B and 2–OH and 4-CF3 substitutions on ring C, along with compound 13, having 2,4-diCl on ring B and 2-OH and 4-CF3 on ring C, were identified as the most potent inhibitors of the targeted AChE and BuChE enzymes, even manifolds more potent than standard donepezil drug. The structures of all synthesized analogues were verified through the utilization of multiple spectroscopic techniques, including HREI-MS and NMR (1H NMR and 13C NMR). The structure-activity relationship (SAR) demonstrated that analogs bearing electron withdrawing groups such as –CF3, –Cl and -NO2 groups displayed superior AChE and BuChE activities. In the molecular docking analysis of the most potent analogs, a favorable protein-ligand interaction (PLI) profile was observed with the respective targets (AChE and BuChE). These interactions encompassed crucial bonding types such as hydrogen bonding, π-π interactions, π-π stacking, and hydrophobic interactions.

Theoretical Study of the Photophysical and Photochemical Properties of 1H‐Benzimidazole and 2‐Ethyl‐7‐nitro‐5‐Substituted 1H‐Benzimidazoles

AbstractTheoretical study of the photophysical/photochemical properties of 1H‐benzimidazole and its derivatives was carried out using APFD, B3LYP, CAM‐B3LYP and PBE0 density functionals with 6‐311+G(2d,p) basis set. The effects of ethanol, 1,4‐dioxane, acetonitrile and water was investigated by means of Integral Equation Formalism of the Polarizable Continuum Model (IEPCM) in the framework of Self‐Consistent Reaction Field (SCRF). The results obtained show that S2 state of the 1H‐benzimidazole molecule is more acidic than the S0 state as the N5−H11 bond length increased to ~ 1.01 Å. At B3LYP/6‐311+G(2d,p) level of theory, the excitation energy of 1H‐bensimidazole molecule in ethanol from S0 to the S2 state was calculated to be 273 nm (4.54 eV). The electronic energy for this transition was calculated to be 0.131 a.u. and observed to occur between π→π* orbitals. Calculations with the PBE0, APFD and B3LYP functionals reproduced the experimental dipole moment in 1,4‐dioxane, with values of 4.09, 4.09 and 4.07 Debye respectively. However, the dipole moments of the 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles were calculated to be higher for electron donating groups (EDGs) than those bearing electron withdrawing groups (EWGs). In addition, the molecular polarizability was observed to increase with decreasing energy gap. Local excitation (LE) and charge‐transfer (CT) were observed to mediate the mechanisms of electronic excitation in 2‐ethyl‐7‐nitro‐5‐substituted‐1H‐benzimidazoles.

Cu(I) Mediated Azidation of Halobenzenes, and Cu Catalysed Selective Azide Reduction to Corresponding Amines

AbstractAryl amines are synthesized from halobenzenes via copper mediated reactions employing sodium azide under mild conditions in ethanol/water. The reaction proceeds stepwise via the aryl azide, which is reduced to the corresponding amine in‐situ. The methodology allows syntheses of amines from corresponding para‐, meta‐ and ortho‐bromobenzenes bearing electron withdrawing groups. Bifunctional halobenzenes bearing alkanoyl chains with terminal bromides are selectively transformed, generating an aniline and an aliphatic azide, as this azide position is stable to reduction. A one‐pot multistep sequence for preparation of the target amines was designed. The azide formation is mediated by CuI while elemental Cu is generated simultaneously, which is deposited onto the employed PTFE stirring bar used in the reaction. The Cu films were quantified and analysed by SEM/EDS. The Cu, either deposited or in solution, is responsible for the azide reduction, possibly involving nitrene intermediates. An application of the modified stirring bars as a heterogeneous catalyst for a click reaction is demonstrated.magnified image

Cesium-Fluoride-Promoted Synthesis of Stable Organocesium Reagents and Their Ambident Reactivities with Arynes.

Described are the diverse reactivities of novel, stable, ambident thio-organocesium reagents (bearing electron withdrawing groups) against benzynes. Reactions at reflux temperature predominantly led to the generation of various functionalized stable sulfonium ylides and at 40 °C the same reaction underwent direct c-arylation. Furthermore, lack of internal hydrogen on the cesium reagent helped to produce different ortho-bifunctional arynes in both the reactions. Interestingly, depending on the reactivities of substrates, the one-pot tri-component procedure generated either ylides or σ-bond insertion products.

Synthesis of 12-Membered Tetra-aza Macrocyclic Pyridinophanes Bearing Electron-Withdrawing Groups.

The number of substituted pyridine pyridinophanes found in the literature is limited due to challenges associated with 12-membered macrocycle and modified pyridine synthesis. Most notably, the electrophilic character at the 4-position of pyridine in pyridinophanes presents a unique challenge for introducing electrophilic chemical groups. Likewise, of the few reported, most substituted pyridine pyridinophanes in the literature are limited to electron-donating functionalities. Herein, new synthetic strategies for four new macrocycles bearing the electron-withdrawing groups CN, Cl, NO2, and CF3 are introduced. Potentiometric titrations were used to determine the protonation constants of the new pyridinophanes. Further, the influence of such modifications on the chemical behavior is predicted by comparing the potentiometric results to previously reported systems. X-ray diffraction analysis of the 4-Cl substituted species and its Cu(II) complex are also described to demonstrate the metal binding nature of these ligands. DFT analysis is used to support the experimental findings through energy calculations and ESP maps. These new molecules serve as a foundation to access a range of new pyridinophane small molecules and applications in future work.

1,2,5]Oxadiazolo[3,4-b]pyrazine-5,6-diamine Derivatives as Mitochondrial Uncouplers for the Potential Treatment of Nonalcoholic Steatohepatitis.

Small molecule mitochondrial uncouplers are emerging as a new class of molecules for the treatment of nonalcoholic steatohepatitis. We utilized BAM15, a potent protonophore that uncouples the mitochondria without depolarizing the plasma membrane, as a lead compound for structure-activity profiling. Using oxygen consumption rate as an assay for determining uncoupling activity, changes on the 5- and 6-position of the oxadiazolopyrazine core were introduced. Our studies suggest that unsymmetrical aniline derivatives bearing electron withdrawing groups are preferred compared to the symmetrical counterparts. In addition, alkyl substituents are not tolerated, and the N-H proton of the aniline ring is responsible for the protonophore activity. In particular, compound 10b had an EC50 value of 190 nM in L6 myoblast cells. In an in vivo model of NASH, 10b decreased liver triglyceride levels and showed improvement in fibrosis, inflammation, and plasma ALT. Taken together, our studies indicate that mitochondrial uncouplers have potential for the treatment of NASH.

Synthesis of Diarylacetylenes Bearing Electron-Withdrawing Groups via the Smiles Rearrangement

Nitrobenzyl benzothiazol-2-yl sulfones and nitrobenzyl 1-phenyl-1H-tetrazol-5-yl sulfones react with chlorides of aromatic acids to form β-acyl derivatives. These products undergo the Smiles rearrangement resulting in the formation of the corresponding nitrophenyl arylacetylenes in 50–60% overall yields (approx. 75% per step). Sulfones bearing CF3 or CN groups instead of a NO2 substituent form mixtures of the acetylenes in moderate yields and benzyl aryl ketones in yields above 40%.

Microwave assisted base-catalyzed 1,3-isomerization of 7-substituted cycloheptatriene bearing electron withdrawing groups

A series of 7-substituted cycloheptatrienes bearing EDG such as (3, X = –PPh3+, –P(O)Ph2, –SO2C6H4CH3, –OCOC6H4CH3 and –CN) were synthesized and their isomerization into the corresponding 2-isomers (4–8) has been achieved, under controlled microwave heating in the presence of easily available DABCO and t-BuOK. On the other hand, the conversion of allyltriphenylphosphonium bromide into vinylic isomer with NEt3 has been carried out in a similar way. This convenient and facile procedure has reduced the average reaction times to a matter of minutes (>20 min), rather than the hours typical of conventional procedures, in addition, the 2-isomers (4–8) were obtained in excellent yields and mechanism of products formation is described.

PtO2/PTSA system catalyzed regioselective hydration of internal arylalkynes bearing electron withdrawing groups

A highly efficient PtO2/PTSA catalyst system for the hydration of a wide array of alkynes was developed. This method proved to be compatible with a large range of functional groups and the ketone products were obtained in high yields. The scope of this methodology was also extended to the synthesis of 3-aryl-isochromenones, -indoles and -benzofurans.

Oxidation of Alcohols by Hydrogen Peroxide Catalyzed by Trinuclear Copper(II) Complex [Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH derived from Disalicylaldehyde Malonoyldihydrazone

Background: The oxidation of alcohols to afford carbonyl compounds is a key transformation in organic chemistry. Significant development has occurred in the recent years, in catalytic oxidation of alcohols by aerial oxygen. However, the alcohol oxidation mediated by H2O2 is quite meagre. From economic and environmental point of views, the oxidation of alcohols mediated by H2O2 is quite attractive in particular. Methods: Various alcohols Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH, ligand, H2O2, CDCl3, Tetramethylsilane were used for oxidation of alcohols to carbonyl compounds. For analysis, IR, 1H NMR, and 13C NMR were utilized. Results: Taking benzyl alcohol as a model compound, first reaction conditions were optimized. The combination of catalyst (0.04 mmol, 0.032 mg), 15% H2O2 (8.83 mmol, 2 mL) at 70°C under solvent free condition was found to be the most appropriate condition for the oxidation of alcohols. The efficiency of the catalyst was tested by oxidizing several aromatic ring substituted benzyllic, aliphatic and allylic alcohols by H2O2. We efficiently carried out oxidation of nineteen alcohols. The benzyl alcohols bearing electron withdrawing groups gave excellent yield of the corresponding carbonyl compounds whereas those bearing electron donating substituent gave slightly lower conversions. The heteroaroyl alcohols also gave excellent yield. The hydroxy group was oxidized selectively to aldehyde in cinnamyl alcohol keeping double bond intact. Secondary alcohols such as cyclohexane and 1-phenylethanol were negligibly oxidized. The aliphatic alcohols gave much lower yield as compared to benzyllic and allylic alcohols. Conclusion: The benzyllic, aliphatic and allylic alcohols were effectively oxidized to aldehydes by hydrogen peroxide using catalytic amount of Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH. The process is simple and mild, the catalyst can be recycled to get improved catalytic activity. Keywords: Catalysts, Oxidation, alcohols, carbonyl compounds, [Cu3(slmh)(µ-Cl)2(CH3OH)3].0.5CH3OH, hydrogen peroxide, spectroscopic study.

Synthesis, Properties, and Light-Emitting Electrochemical Cell (LEEC) Device Fabrication of Cationic Ir(III) Complexes Bearing Electron-Withdrawing Groups on the Cyclometallating Ligands.

The structure–property relationship study of a series of cationic Ir(III) complexes in the form of [Ir(C^N)2(dtBubpy)]PF6 [where dtBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine and C^N = cyclometallating ligand bearing an electron-withdrawing group (EWG) at C4 of the phenyl substituent, i.e., −CF3 (1), −OCF3 (2), −SCF3 (3), −SO2CF3 (4)] has been investigated. The physical and optoelectronic properties of the four complexes were comprehensively characterized, including by X-ray diffraction analysis. All the complexes exhibit quasireversible dtBubpy-based reductions from −1.29 to −1.34 V (vs SCE). The oxidation processes are likewise quasireversible (metal + C^N ligand) and are between 1.54 and 1.72 V (vs SCE). The relative oxidation potentials follow a general trend associated with the Hammett parameter (σ) of the EWGs. Surprisingly, complex 4 bearing the strongest EWG does not adhere to the expected Hammett behavior and was found to exhibit red-shifted absorption and emission maxima. Nevertheless, the concept of introducing EWGs was found to be generally useful in blue-shifting the emission maxima of the complexes (λem = 484–545 nm) compared to that of the prototype complex [Ir(ppy)2(dtBubpy)]PF6 (where ppy = 2-phenylpyridinato) (λem = 591 nm). The complexes were found to be bright emitters in solution at room temperature (ΦPL = 45–66%) with microsecond excited-state lifetimes (τe = 1.14–4.28 μs). The photophysical properties along with density functional theory (DFT) calculations suggest that the emission of these complexes originates from mixed contributions from ligand-centered (LC) transitions and mixed metal-to-ligand and ligand-to-ligand charge transfer (LLCT/MLCT) transitions, depending on the EWG. In complexes 1, 3, and 4 the 3LC character is prominent over the mixed 3CT character, while in complex 2, the mixed 3CT character is much more pronounced, as demonstrated by DFT calculations and the observed positive solvatochromism effect. Due to the quasireversible nature of the oxidation and reduction waves, fabrication of light-emitting electrochemical cells (LEECs) using these complexes as emitters was possible with the LEECs showing moderate efficiencies.

Metal-Free Photocatalyzed Cross Coupling of Bromoheteroarenes with Pyrroles

The excited radical anion of rhodamine 6G reduces heteroaryl bromides and chlorides to generate heteroaryl radicals that were successively trapped by pyrroles for the synthesis of heteroaromatic biaryls in moderate to excellent yields. The synthetically important photoredox catalytic C–H heteroarylation reaction works for a broad range of brominated electron-rich heteroarenes and chlorinated heteroarenes bearing electron withdrawing groups. In addition, this methodology was applied to the formal synthesis of a benzimidazole derivative II with interesting pharmacological properties.

Chemical synthesis, pharmacological evaluation and in silico analysis of new 2,3,3a,4,5,6-hexahydrocyclopenta[c]pyrazole derivatives as potential anti-mitotic agents

We have synthesized new, biologically active mono- and di-substituted 2,3,3a,4,5,6-hexahydrocyclopenta[c]pyrazole derivatives bearing electron withdrawing groups and electron donating groups. These derivative structures were characterized by their spectral and analytical data. The newly synthesized hexahydropyrazole analogues were evaluated for their in vitro anticancer activity against breast and lung cancer cell lines using a cytotoxicity bioassay. To understand their mechanism of action, tubulin binding assays were performed which pointed to their binding to microtubules in a mode similar to but not identical to colchicine, as evidenced by their KD value evaluation. Computational docking studies also suggested binding near the colchicine binding site on tubulin. These results were further confirmed by colchicine-binding assays on the most active compounds, which indicated that they bound to tubulin near but not at the colchicine site. The moderate cytotoxic effects of these compounds may be due to the presence of electron donating groups on the para-position of the phenyl ring, along with the hexahydropyrazole core nucleus. The observed anti-cancer activity based on inhibition of microtubule formation may be helpful in designing more potent compounds with a hexahydropyrazole moiety.

ChemInform Abstract: Asymmetric Synthesis of Fluorinated Isoindolinones Through Palladium‐Catalyzed Carbonylative Amination of Enantioenriched Benzylic Carbamates.

AbstractDuring the carbonylation process, a significant loss of optical purity is observed for substrates bearing electron withdrawing groups.

ChemInform Abstract: Nickel‐Catalyzed Suzuki—Miyaura Type Cross‐Coupling Reactions of (2,2‐Difluorovinyl)benzene Derivatives with Arylboronic Acids.

AbstractThe reaction fails using gem‐difluoroalkenes bearing electron withdrawing groups, aliphatic or hetaryl substituents.

ChemInform Abstract: Pillar[n]arenes and Other Cavitands: Aspects of Complex Thermodynamics

AbstractReview: 67 refs.

Pillar[n]arenes and Other Cavitands: Aspects of Complex Thermodynamics

AbstractNovel cavitands, the pillar[n]arenes, have captivated the attention of supramolecular chemists since the first reported synthesis of pillar[5]arene displaying binding capability to guest molecules. Recently, pillar[n]arenes and their functionalized pillar[n]arenes have been applied in many different areas, from supramolecular chemistry to materials science. Pillar[n]arenes have symmetric pillar shapes, and consist of n hydroquinone units bridged by methylene groups, which link the 2‐ and 5‐positions of the hydroquinone units. The inner surface of the cavity of pillar[n]arenes is π‐electron‐rich, thus providing a favorable environment for guest molecules bearing electron withdrawing groups. Despite the extensive efforts, however, the complex thermodynamics of pillar[n]arenes have not been systematically investigated to date. This review outlines the range and perspectives of the thermodynamic characteristics of pillar[n]arenes in comparison with other successful cavitands, such as cyclodextrins and cucurbit[n]urils.