Nucleophilic Aromatic Substitution Reaction Research Articles

1,2,5]Thiadiazolo[3,4-d]Pyridazine as an Internal Acceptor in the D-A-π-A Organic Sensitizers for Dye-Sensitized Solar Cells.

Four new D-A-π-A metal-free organic sensitizers for dye-sensitized solar cells (DSSCs), with [1,2,5]thiadiazolo[3,4-d]pyridazine as internal acceptor, thiophene unit as π-spacer and cyanoacrylate as anchoring electron acceptor, have been synthesized. The donor moiety was introduced into [1,2,5]thiadiazolo[3,4-d]pyridazine by nucleophilic aromatic substitution and Suzuki cross-coupling reactions, allowing design of D-A-π-A sensitizers with the donor attached to the internal heterocyclic acceptor not only by the carbon atom, as it is in a majority of DSSCs, but by the nitrogen atom also. Although low values of power conversion efficiency (PCE) were found, a few important consequences were identified: (i) poor PCE data can be attributed to high electron deficiency of the internal [1,2,5]thiadiazolo[3,4-d]pyridazine acceptor due to lower light harvesting by the dye; (ii) the manner in which the donor was attached to the internal acceptor (by carbon or nitrogen) did not play an essential role in the photovoltaic properties of the dyes; (iii) dyes based on the novel donor 2,3,4,4a,9,9a-hexahydro-1H-1,4-methanocarbazolyl and 9-(p-tolyl)-2,3,4,4a,9,9a-hexahydro-1H- carbazole moieties showed similar photovoltaic properties to dyes based on the well-known 4-(p-tolyl)-1,2,3,3a,4,8b-hexahydrocyclopenta[b]indolyl building block, which opens the door for further optimization potential of new dye families.

3-Substituted Benzo[ e][1,2,4]triazines: Synthesis and Electronic Effects of the C(3) Substituent.

A series of 19 structurally diverse C(3)-substituted derivatives of benzo[ e][1,2,4]triazine were synthesized from 3-chloro- (1c) and 3-iodobenzo[ e][1,2,4]triazine (1d) obtained in three steps from 2-nitroaniline in 37-55% yields. Nucleophilic aromatic substitution and metal-catalyzed (Pd, Cu) reactions led to functional derivatives that include alkyl (C5H11), (het)aryl (Ph, 2-thienyl, ferrocenyl), ArC≡C, amine (NHPh and morpholine), PO(OEt)2, sulfanyl (SBu- t), alkoxide (OEt, OMe), and CN. The synthesis of C(3)-CF3 derivative 1g via the Ruppert reaction with 1d and its 1-oxide analogue 2d led to the substitution followed by formal addition of HCF3 to the C═N bond. Pd-catalyzed carbonylation reactions of 1d and 2d did not give the corresponding C(3)-carboxylic acids. Therefore, acid 1f was obtained through hydrolysis of the CN. The substituent effect on the electronic structure of the benzo[ e][1,2,4]triazine ring was investigated by spectroscopic methods (UV-vis and NMR) augmented with density functional theory calculations. Results show significant effect of the C(3) substituent on the π-π*(1) transition energy and good correlation of the 1H NMR chemical shift with the substituent constant σp. Molecular and crystal structures of six derivatives were established with the single-crystal X-ray diffraction method, and the substituent impact on the molecular geometry was investigated.

Post-functionalization of perfluorocyclobutyl aryl ether polymers with a novel perfluorosulfonated side chain precursor

To develop a new approach to prepare sulfonated perfluorocylobutyl (PFCB) aryl ether polymers, post-functionalization of PFCB aryl ether polymers with a novel perfluorosulfonated side chain precursor was described in this study. The precursor was firstly designed and synthesized from 4-(2-bromo-1,1,2,2-tetrafluoroethoxy) phenol and hexafluorobenzene via nucleophilic substitution, followed by sulfinatodehalogenation and oxidation. Then a series of novel sulfonated PFCB aryl ether polymers (FS-PFCB-x) was successfully prepared from the precursor by a nucleophilic aromatic substitution reaction. The components of the precursor were investigated by fourier transform infrared spectroscopy, nuclear magnetic resonance (NMR) spectroscopy and high resolution mass spectrometry. The chemical structures of FS-PFCB-x polymers were characterized by NMR spectroscopy. FS-PFCB-xx polymers exhibited good thermal stability with decomposition temperatures up to 200 °C, and good solubility in polar aprotic solvents as dimethyl sulfoxide, N,N-dimethylformamide and N,N-dimethylacetamide.

One-Pot Approach for SNAr Reaction of Fluoroaromatic Compounds with Cyclopropanol

A novel method for preparing aromatic compounds containing cyclopropoxy via nucleophilic aromatic substitution reaction (SNAr) of fluoroaromatic compounds with cyclopropanol under relatively mild conditions is presented. As compared to the approaches reported previously for preparing 1-(cyclopropyloxy)-2-nitrobenzene, the one proposed in this work is simplified without sacrificing the yields: When the reaction was performed at 75 °C with Cs2CO3 as the base and DMF as solvent, after 6 h the yield was up to 90%. Finally, various fluoroaromatic compounds were employed as substrates for a test that proves a wide application scope of the method.

Chemically stable polyarylether-based covalent organic frameworks.

The development of crystalline porous materials with high chemical stability is of paramount importance for their practical application. Here, we report the synthesis of polyarylether-based covalent organic frameworks (PAE-COFs) with high crystallinity, porosity and chemical stability, including towards water, owing to the inert nature of their polyarylether-based building blocks. The PAE-COFs are synthesized through nucleophilic aromatic substitution reactions between ortho-difluoro benzene and catechol building units, which form ether linkages. The resulting materials are shown to be stable against harsh chemical environments including boiling water, strong acids and bases, and oxidation and reduction conditions. Their stability surpasses the performance of other known crystalline porous materials such as zeolites, metal-organic frameworks and covalent organic frameworks. We also demonstrate the post-synthetic functionalization of these materials with carboxyl or amino functional groups. The functionalized PAE-COFs combine porosity, high stability and recyclability. A preliminary application of these materials is demonstrated with the removal of antibiotics from water over a wide pH range.

SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL EVALUATION OF SUBSTITUTED 2-PHENOXY-NICOTINALDEHYDES AS α-AMYLASE INHIBITOR

Diabetes mellitus is a chronic endocrine disorder that affects the metabolism of carbohydrates, proteins, fat, electrolytes and water. α -Amylase and α -glucosidase are the important enzymes required for the digestion of the carbohydrate. These enzymes plays a vital role in the breakdown of starch in the diet and its activity has been correlated to postprandial blood glucose levels, the control of which is essential for maintaining quality of life for diabetic patients. We report the synthesis, characterization and biological evaluation of new substituted 2-phenoxynicotinaldehydes as α -amylase inhibitors. A new general method based on the aromatic nucleophilic substitution reactions of 2-chloronicotinaldehyde with different substituted phenols in presence of K 2 CO 3 in dry dioxane was developed to furnish the corresponding substituted 2-phenoxynicontinaldehydes with 70-80% yields.

Scalable Process Design for a PDE10A Inhibitor Consisting of Pyrazolopyrimidine and Quinoxaline as Key Units

In this study, research and development for the synthetic process of a PDE10A inhibitor are described; in particular, an efficient regioselective construction of the quinoxaline unit, a cost-effective pyrazolo[1,5-a]pyrimidine formation, and a cost-saving approach in a nucleophilic aromatic substitution (SNAr) reaction by introducing oxazolidinone as an electron-withdrawing group to a chloropyrazolo[1,5-a]pyrimidine core are key points. The newly developed process has been successfully scaled up to 40 kg. Furthermore, a one-pot tandem reaction from aminopyrazole to dichloropyrazolo[1,5-a]pyrimidine by activating malonic acid with POCl3 was discovered. The finding contributed to avoiding isolation of the hygroscopic pyrazolo[1,5-a]pyrimidin-5(4H)-one intermediate, which caused complicated filtration and drying processes observed in the first scale-up campaign.

Diimidazo[4,5-b:4′,5′-e]pyridine: synthesis and nucleophilic aromatic substitution reaction

1,7-Dihydrodiimidazo[4,5-b:4′,5′-e]pyridine obtained by reductive heterocyclization was N-arylated with 4-fluoronitrobenzene to form two regioisomers in 7 : 3 ratio. This N-arylation is considered as a model reaction for the polymer synthesis.

Substrate-Driven Transient Self-Assembly and Spontaneous Disassembly Directed by Chemical Reaction with Product Release.

The chemical reactivity of molecules can be significantly enhanced when they are trapped in a confined space. Although such a confinement effect can be found in many self-assembled nanostructures, dissipation after completing the reaction to release the product remains elusive. Here we report substrate-directed transient self-assembly for accelerating a chemical reaction and spontaneous disassembly with releasing the products. The hydrophobic substrates mediate self-assembly of a dissolved pyridine-based amphiphile to provide a confined space to promote an aromatic nucleophilic substitution (SNAr) reaction in water. The chemical reaction triggers disassembly of the aggregates with simultaneous release of the product that can be spontaneously separated out of the solution by precipitation. Neutralization of the amphiphilic molecule leads to a new cycle of self-assembly entrapping substrates and disassembly with releasing the product.

Synthesis and fluorescent properties of N(9)-alkylated 2-amino-6-triazolylpurines and 7-deazapurines.

The synthesis of novel fluorescent N(9)-alkylated 2-amino-6-triazolylpurine and 7-deazapurine derivatives is described. A new C(2)-regioselectivity in the nucleophilic aromatic substitution reactions of 9-alkylated-2,6-diazidopurines and 7-deazapurines with secondary amines has been disclosed. The obtained intermediates, 9-alkylated-2-amino-6-azido-(7-deaza)purines, were transformed into the title compounds by CuAAC reaction. The designed compounds belong to the push–pull systems and possess promising fluorescence properties with quantum yields in the range from 28% to 60% in acetonitrile solution. Due to electron-withdrawing properties of purine and 7-deazapurine heterocycles, which were additionally extended by triazole moieties, the compounds with electron-donating groups showed intramolecular charge transfer character (ICT/TICT) of the excited states which was proved by solvatochromic dynamics and supported by DFT calculations. In the 7-deazapurine series this led to increased fluorescence quantum yield (74%) in THF solution. The compounds exhibit low cytotoxicity and as such are useful for the cell labelling studies in the future.

Synthesis of 6-Amino- and 6-Arylazoazulenes via Nucleophilic Aromatic Substitution and Their Reactivity and Properties.

The nucleophilic aromatic substitution (SNAr) reaction of diethyl 6-bromoazulene-1,3-dicarboxylate (1) with a variety of amines afforded the corresponding 6-aminoazulene derivatives 2a-2j in good-to-excellent yields. 6-Aminoazulene derivatives 3a-3f without the 1,3-diethoxycarbonyl functions were obtained by the deesterification of 2a-2f with 100% H3PO4. The reactivity of 6-aminoazulenes toward the bromination, SNAr, and palladium-catalyzed cross-coupling reactions was also clarified. 6-Arylazoazulenes 13a-13c were also prepared via the SNAr reaction of 1 with arylhydrazines, followed by oxidation with Pb(OAc)4 in the presence of N2H4. The structural, optical, and electrochemical properties of the 6-amino- and 6-arylazoazulenes were revealed by single-crystal X-ray structure analysis, UV/vis spectroscopy, voltammetry analysis, spectroelectrochemistry, and theoretical calculations.

Theoretical Insights into the Reaction Mechanism between 2,3,7,8-Tetrachlorodibenzofuran and Hydrogen Peroxide: A DFT Study.

A detailed knowledge of the reactivity of 2,3,7,8-tetrachlorodibenzofuran (TCDF) at the molecular level is important to better understand the transformation of dioxins analogous to TCDF in the environment. To clarify the reactivity of the organic hydroperoxides toward TCDF, the reaction of the TCDF with hydrogen peroxide (H2O2) and its anion has been investigated theoretically. For the reaction of the neutral H2O2, a molecular complex can be formed between TCDF and H2O2 first. Then, the nucleophilic aromatic substitution of TCDF by H2O2 occurs in the presence of the water molecules to form an intermediate containing an O–O bond. Finally, the O–O bond cleavages homolytically for the above intermediate. On the other hand, as for the reaction of the anion of H2O2 (HO2–), the nucleophilic addition of HO2– to TCDF can also occur besides the nucleophilic aromatic substitution reaction mentioned above, resulting in the dissociation of the C–O bond of TCDF. Unlike the reaction involving neutral H2O2, no water molecules are required. In addition, the selected substitution effects, such as F-, Br-, and CH3-substituents, on the reactivity of the above reaction have also been explored. Hopefully, the present results can enable us to gain insights into the reactivity of the organic hydroperoxides with TCDF-like environmental pollutants.

Direct synthesis of covalent triazine-based frameworks (CTFs) through aromatic nucleophilic substitution reactions.

Despite extensive efforts, only three main strategies have been developed to synthesize covalent triazine-based frameworks (CTFs) thus far. We report herein a totally new synthetic strategy which allows C–C bonds in the CTFs to be formed through aromatic nucleophilic substitution reactions. The as-synthesized CTF-1 and CTF-2 exhibited photocatalytic water splitting activity comparable to the CTFs made using ionothermal or Brønsted acid-catalyzed polymerization. Interestingly, CTF-2 distinguished itself by its two-photon fluorescence (emission at ∼530 nm under irradiation at either 400 nm or 800 nm).

Novel 4,4'-Fluoresceinoxy Bisphthalonitrile Showing Aggregation-Induced Enhanced Emission and Fluorescence Turn off Behavior to Fe3+ Ions.

A novel 4,4'-fluoresceinoxy bisphthalonitrile FPN is synthesized from fluorescein and 4-nitrophthalonitrile by aromatic nucleophilic ipso nitro substitution reaction. The structure of FPN constitutes phthalonitrile-fluorescein-phthalonitrile, acceptor-donor-acceptor, A-D-A form and the solvatochromic study of newly synthesized compound FPN was done in hexane, cyclohexane, CHCl3, DCM, DMF, acetonitrile, ethanol and in methanol. The aggregation behavior of FPN was investigated in good-poor solvent mixture DMF-water in various proportions and the molecule was found to be exhibiting Aggregation Induced Emission Enhancement AIEE for volume percentage of water beyond 50% with a significant hypsochromic shift of 70nm in the emission maxima from 458 to 388nm. This phenomenon is termed as Aggregation Induced Blue Shifted Emission Enhancement AIBSEE and was reported in substituted phthalonitrile for the first time. The chemo sensing activity of FPN with various transition metal ions also has been checked by fluorescence spectroscopy where the new molecule FPN exhibited fluorescence turn OFF behaviour towards Fe3+ ion in acetonitrile-methanol ACN-MeOH solution. The binding stoichiometry of FPN with Fe3+ was verified by Job's plot analysis and Density Functional Theory DFT-B3LYP computational methodology by using Gaussian 09 software. Graphical Abstract A novel 4,4'-fluoresceinoxy bisphthalonitrile FPN was synthesized by base catalyzed coupling reaction of fluorescein with 4 nitrophthalonitrile. The newly synthesized compound has been characterized using UV-vis, FTIR, 1HNMR, fluorescence spectral data and single crystal X-ray diffraction studies. The compound FPN was found to be exhibiting positive solvatochromism in various organic solvents and Aggregation Induced Blue Shifted Emission Enhancement AIBSEE in DMF-aqueous mixture when water volume exceed above 50%. As a metal ion chemo sensor FPN exhibited a selective fluorescence turn OFF behavior towards Fe3+ ion in the stoichiometric ratio 1:2 in acetonitrile-methanol mixture and limit of detection LOD of Fe3+ by FPN was calculated to be 3.665μM.

Divergent synthesis of 5',7'-difluorinated dihydroxanthene-hemicyanine fused near-infrared fluorophores.

We describe an expedient access to a 5',6',7'-trifluoro dihydroxanthene-hemicyanine fused scaffold in 2 steps and 54% overall yield from the corresponding salicylic aldehyde. A 6'-regioselective nucleophilic aromatic substitution (SNAr) reaction with a wide range of nitrogen, sulfur or selenium nucleophiles then gives access to 16 near-infrared (NIR) fluorophores emitting in the 710-750 nm range. We also report the experimental and theoretical photophysical investigations of these unique optical agents that include the first series of 6'-heavy atom substituted dihydroxanthenes, extending the pool of polyfluorinated markers for biomedical and material applications.

σ-Holes promote the concertedness in nucleophilic aromatic substitution reactions of nitroarenes

Concertedness in SNAr may be modulated by the presence of a σ-hole.

Novel Blue‐Emitter‐Containing o‐Terphenyl‐Substituted Fluorene and Diphenylanthracene Units

AbstractThe light emitting polymers (LEPs) were synthesized by aromatic nucleophilic substitution reaction containing o‐terphenyl substituted fluorene (TERF) and diphenylanthracene (DPA) units. The obtained polymers showed emission in the blue region. The polymers were successfully characterized by elemental analysis, FTIR and 1H NMR spectroscopic studies. Polymers were thermally stable and soluble in various organic solvents. The electrochemical measurements and optical properties of the polymers were also studied. These light emitting materials showed high photoluminescence efficiency, making them good candidates as organic materials for light‐emitting devices.

A dual-responsive fluorescent probe for detection of fluoride ion and hydrazine based on test strips.

Hydrazine (N2H4) and fluoride ion (F-) are regarded as environmental pollutants and potential carcinogens. A dual-functional fluorescent probe (probe 1) was developed for both F- and N2H4 with high selectivity and sensitivity. 1 was based on nucleophilic aromatic substitution reaction for N2H4 detection and selective cleavage of 4-nitrobenzenesulphonyl group for the determination of F-. The limits of detection of probe for F- and N2H4 were 77.82 nM and 29.34 nM, respectively, which are far below the threshold limit value (TLV) of United States Environmental Protection Agency (EPA). The home-made test strips of 1 provided the positive tool for F- and gaseous N2H4 in different system. And the confocal fluorescence images indicated that 1 can quantitatively detect N2H4 in living PC12 cells. Promisingly, 1 has great prospects for N2H4 imaging and determining in living system.

Contrasting Reactivity of 2‐chloro‐1‐formyl‐3‐hydroxymethylenecyclohexene and its Schiff Bases towards Disodium Diselenide: Isolation of Selenospirocycles versus Azapentalenes

AbstractA convenient approach for the synthesis of alicyclic selenospirocycles, 24 and 25, stabilized by intramolecular chalcogen bonding (IChB) is reported by the reaction of 5‐alkyl‐2‐chloro‐1‐formyl‐3‐hydroxymethylenecyclohexene derivatives {alkyl=H (22), Me (23)} with in situ generated disodium diselenide (Na2Se2). However, when 2‐chloro‐1‐formyl‐3‐hydroxymethylenecyclohexene, 22 is condensed with aniline or 4‐methoxyaniline and the resulting Schiff bases 26 and 27 are subjected to identical reactions, the Schiff bases undergo cyclisation to afford brightly colored, fused 1,6‐diaza‐6a‐selenapentalene derivatives 28–29, instead of the expected selenospirocycles. The aromatic nucleophilic substitution (SNAr) reaction of N‐(2‐bromo‐3‐nitrobenzyl)naphthylamine, 33 with nBuSeLi affords N‐[2‐(butylselanyl)‐3‐nitrobenzyl]naphthylamine, 34. The bromination of 34 results in the formation of cyclic isoselenazolines, 35. Selenospirocycles 24 and 25, 1,6‐diaza‐6a‐selenapentalenes 28 and 29 and isoselenazoline 35 are authenticated by single‐crystal X‐ray diffraction studies. Compounds 24, 25 and 35 are stabilized by intramolecular secondary interactions.

Synthesis and Photophysical Properties of a Series of Novel Porphyrin Dendrimers Containing Organoiron Complexes

This article is focused on the design and photophysical properties of a series of novel porphyrin and metalloporphyrin dendrimers containing cationic η6-chloroarene-η5-cyclopentadienyliron(II) complexes functionalized with naphthalene and capped with ferrocene. The incorporation of cationic η6-chloroarene-η5-cyclopentadienyliron moieties into the dendrimer structures enhances solubility, and facilitates nucleophilic aromatic substitution and addition reactions due to the intense electron-withdrawing ability of the iron center. Divergent approaches were employed to yield highly symmetrical branched materials, with interesting and potentially useful properties. The preparation of these dendrimers was achieved via metal-mediated nucleophilic aromatic substitutions and Steglich esterifications. These dendrimers and their precursors were characterized through nuclear magnetic resonance spectroscopy, infrared spectroscopy, and UV–Visible and fluorescence spectroscopy. Substitution on the porphyrin core with various side chains and terminal functional groups and chromophores had little impact on the porphyrin emission properties, allowing for a wide variety of fluorescent macromolecules to be prepared which retain this characteristic emission. Also, the presence or absence of the organopyrene moieties also had little effect on the emission from these compounds. Complexation of a metal cation, such as Zn2+, by these compounds, did however result in a significant blue shift in the observed fluorescence; this interesting result has the potential for applications in the development of fluorescent-based cation sensors.