Aromatic Substitution Products Research Articles

Heteroleptic Dirhodium(II) Complexes with Redox‐Active Ferrocenyl Ligands: Synthesis, Electrochemical Properties, and Redox‐Responsive Chemoselectivity in Carbene C−H Insertion

AbstractA series of original heteroleptic dirhodium(II) complexes (4 a–j) of formula [Rh2(OAc)3(L)], where L is a redox‐active ferrocenecarboxylate ligand, has been prepared. These dirhodium(II) complexes have been characterised by NMR, mass spectrometry and cyclic voltammetry. All complexes show a quasi‐reversible redox behaviour for the ferrocenyl unit. The latter can be selectively oxidised by [N(4‐C6H4Br)3]+BF4−. Four selected heteroleptic complexes 4 a, 4 b, 4 f and 4 i, have been evaluated as catalysts for the intramolecular decomposition of a diazo compound 5. The ratio between the aromatic substitution product 6 and the aliphatic C−H insertion product 7 increases (up to 19 % increase) when using the in situ generated oxidised form of the dirhodium(II) complexes (4 a+BF4− to 4 i+BF4−). This shows that the oxidation of the ferrocenecarboxylate ligand has an effect on the chemoselectivity of the dirhodium‐catalysed diazo decomposition, and thus that the electronic properties of a complex can be tuned without exchanging ligands.

Aromatic nucleophilic substitution: A case study of the interaction of a lithiated nitronyl nitroxide with polyfluorinated quinoline-N-oxides

A 4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl lithium derivative was found to react with 5,6,7,8-tetrafluoro- or 5,7,8-trifluoro-6-(trifluoromethyl)quinoline-N-oxides with the formation of products of aromatic nucleophilic substitution of the H atom at position 2 of the quinoline ring. The reaction regioselectivity is supported by the data of quantum-chemical calculations. Molecular and crystal structures of the obtained nitronyl nitroxides were solved by monocrystal X-ray diffraction analysis, and the nature of the radical was ascertained by electron spin resonance spectroscopy. Heterospin complexes of Cu(hfac)2 with the synthesized quinoline-substituted nitronyl nitroxides were prepared. According to X-ray diffraction analysis, seven-membered metallocycles are formed in the complexes owing to simultaneous coordination of the nitroxyl and N-oxide groups by the Cu atom.

Modification of Polyfluoro-Containing 3-(Ethoxycarbonyl)flavones by Biogenic Amines and Amino Acids

Aim and Objective: The objective of our work was to study the peculiarities of transformations of fluorine-containing flavone-3-carboxylates with N-nucleophiles, including biogenic amines and amino acids. Materials and Methods: 6,7,8-Trifluoro and 5,6,7,8-tetrafluoroflavone-3-carboxylates were involved in interactions with a number of N-nucleophiles, such as pyrrolidine, morpholine, proline, arginine, gammaaminobutyric acid, beta-alanine, histamine, dopamine and amantadine under different reaction conditions. All synthesized compounds were characterized by NMR 1H, 19F, (NMR 13C for some compounds) and IR spectroscopic data, and elemental analysis. Results: 3-(Ethoxycarbonyl)polyfluoroflavones react with morpholine, pyrrolidine and L-proline to form 7- monosubstituted flavone-3-carboxylates. For the reactions of tetrafluoroflavone with pyrrolidine and morpholine, the formation of 5,7-disubstituted products is also possible. Interaction with gamma-aminobutyric acid leads to the 4-{[3-ethoxy-2-(2-hydroxypolyfluorobenzoyl)-3-oxo-1-phenylprop-1-enyl]amino}butanoic acids as a result of the pyrone ring opening. In reactions with dopamine, histamine, L-arginine and β-alanine, polyfluoroflavone-3-carboxylates underwent a chromone-coumarin rearrangement. 3-(Ethoxycarbonyl)tetrafluoroflavone forms with amantadine the nucleophilic aromatic substitution product, while trifluoro-substituted analog gives the chromone-coumarin rearrangement product. Conclusion: This work showed possibilities of chemical modification of polyfluorinated flavones in the reactions with amines depending on the structure of the nucleophilic reagent. Synthesized compounds are of interest for biological testing.

5-Amino-Substituted Derivatives of 4-Nitrofurazane: Synthesis, Structure, and Biological Activity

New amination reactions of 5-chloro-4-nitrobenzofurazane with different amines were studied. The reactions of 5-chloro-4-nitrobenzofurazane with 2,4,6-trichloro-, para-acetyl-, and para-carboxyethylanilines gave the products of aromatic nucleophilic substitution of the chlorine substituent in the nitrogenous heterocycle, the composition and structure of which was established by chemical, physical, and physicochemical methods and X-ray diffraction analysis. The thermal stability was studied by synchronous thermogravimetry and differential scanning calorimetry (TG‒DSC). The synthesized compounds showed a high antibacterial and antimycotic activity against human and animal pathogenic microflora.

The First Triple-Decker Complex with a Carbenium Center, [CpCo(μ-C3 B2 Me5 )RuC5 Me4 CH2 ]+ : Synthesis, Reactivity, X-Ray Structure, and Bonding.

The first derivative of the methylium cation with the triple-decker substituent, [CpCo(C3 B2 Me5 )RuC5 Me4 CH2 ]PF6 (2PF6 ), was synthesized from the reaction of the triple-decker complex CpCo(C3 B2 Me5 )RuCp* (1) with the salt of the trityl cation [CPh3 ]+ . The X-ray crystal structure of 2PF6 reveals that the methylium carbon is bound to the ruthenium with Ru-C bond length of 2.259 Å and corresponds to the description of its structure as η6 -fulvene-ruthenium. Reactions of 2PF6 with nucleophiles OH- , Ph3 P, Et3 N led to the corresponding derivatives of 1 in high yields. Aromatic amines PhNEt2 and 4-MeC6 H4 NH2 react with 2PF6 to give the electrophilic aromatic substitution products quantitatively. Chemical reduction of 2PF6 with Zn powder in tetrahydrofuran leads to the formation of the bis(triple-decker) derivative (CpCo(C3 B2 Me5 )RuC5 Me4 CH2 )2 (10) with a CH2 CH2 -bridge. The structures of complexes 4, 7-10 were determined by X-ray diffraction. Density functional calculations support the crystallographically determined geometry of 2 and allow rationalization of some characteristics of its structure, spectroscopy, and reactivity.

Treatment of PCB‐Laden Transformer Oil with Polyethylene Glycols and Alkaline Hydroxide

The direct disposal of polychlorinated biphenyls (PCBs) in transformer oil by polyethylene glycols (PEGs) under basic condition is reported. The transformer oil containing PCBs was treated by the required amounts of PEGs and potassium hydroxide (KOH) for different reaction times and temperatures. Complete reaction produces aryl PEGs, which are the products of nucleophilic aromatic substitution. The relative efficiencies of the PCB treatment process were assessed in terms of destruction and removal efficiency (DRE, %). At the experimental conditions of 100 °C and 7 h, 125 °C and 3 h, and 150 °C and 1 h, average DREs of PCBs better than 99.9999% were attained. In studying the chemical reaction of PCBs with PEG/KOH, it was confirmed that the process led to less chlorinated PCBs through a stepwise process with the successive elimination of chlorines. Particularly, the least chlorinated PCBs such as mono‐ and di‐PCBs were not produced in our study. Furthermore, the treated transformer oil can be reused through simple segregating procedures.

Versatile reactivity of amines towards the ruthenocenylmethylium cation [Cp*Ru(C5Me4CH2)

The cationic complex [Cp*Ru(C 5 Me 4 CH 2 )] + reacts with Et 3 N primarily giving the ammonium salt [Cp*Ru(C 5 Me 4 CH 2 NEt 3 )] + . The prolonged standing of the reaction mixture results in the formation of the ether Cp*Ru(C 5 Me 4 CH 2 OCH 2 C 5 Me 4 )RuCp*. The reaction of [Cp*Ru(C 5 Me 4 CH 2 )] + with PhNEt 2 leads to the electrophilic aromatic substitution product [Cp*Ru(C 5 Me 4 CH 2 C 6 H 4 NHEt 2 )] + .

Dehalogenation of arenes via SN2 reactions at bromine: competition with nucleophilic aromatic substitution.

The gas-phase reactions of carbon- and nitrogen-centered nucleophiles with polyfluorobromobenzenes were examined in a selected-ion flow tube (SIFT) and modeled computationally at the MP2/6-31+G(d,p)//MP2/6-31+G(d) level. In the gas-phase experiments, rate constants and branching ratios were determined. The carbon nucleophiles produce expected nucleophilic aromatic substitution (SNAr) and proton transfer products along with unexpected products that result from SN2 reactions at the bromine center (polyfluorophenide leaving group). With nitrogen nucleophiles, the SN2 at bromine channel is suppressed. In the SNAr channels, the "element effect" is observed, and fluoride loss competes with bromide loss. The computational modeling indicates that all the substitution barriers are well below the entrance channel and that entropy and dynamics effects control the product distributions.

Reaction of (Z)-5-(Bromomethylene)thiophen-2(5H)-one with Some Nucleophiles in Search for New Biofilm Inhibitors

(Z)-5-(Bromomethylene)thiophen-2(5H)-one reacts in a Michael-type addition across the methylene side chain with nucleophiles followed by elimination of bromide. The reaction was done at room temperature and the yields were good. The aromatic sulfur substitution products showed potent activity as biofilm inhibitors.

Direct β-amination reaction in porphyrin systems—a simple route to compounds containing two nitrogen substituents at both β-positions of the same pyrrole unit

The direct β-amination of porphyrin derivatives is described. 2-Nitro-meso-tetraarylporphyrins (zinc and copper complexes) react with N,N,N-trimethylhydrazinium iodide (TMHI) in the presence of a base (KOH/DMSO system, ca 70–80°C) to give products of nucleophilic aromatic substitution of hydrogen. In this process, the nucleophilic replacement of a H-atom by an NH2 group takes place. The products obtained, bearing two neighbouring nitrogen substituents on the same pyrrole ring, are valuable intermediates for various synthetic uses.

PCBs 함유 변압기 절연유의 화학적처리

Practical disposal of transformer insulation oil laden with PCBs (polychlorinated biphenyls) by a chemical treatment has been studied in field work. The transformer insulation oil containing PCBs was treated by the required amounts of PEG (polyethylene glycol) and KOH, along with different reaction conditions such as temperatures and times. The reaction of PEG with PCBs under basic condition produces arylpolyglycols, the products of nucleophilic aromatic substitution. Removal efficiencies of PCBs in insulation oil before and after chemical treatment were examined. The removal efficiency of PCBs was very low at lower temperatures of 25 and <TEX>$50^{\circ}C$</TEX>. Under the reaction condition of PEG 600/KOH/<TEX>$100^{\circ}C$</TEX>/2hr, removal efficiency of PCBs was approximately 70%, showing completely removal of PCBs containing 7~9 chlorines on biphenyl frame which appear later than PCB IUPAC Number 183 (2,2',3,4,4',5',6-heptaCB) in retention time of GC/ECD. However, when increasing the reaction temperature and time to <TEX>$150^{\circ}C$</TEX> and 4 hours, removal efficiency of PCBs reached 99.99% without any formation of PCDDS/PCDFs during the process. Such reaction conditions were verified by several official analytical institutions. In studying the reaction of PEG with PCBs, it confirmed that the process of chemical treatment led to less chlorinated PCBs through a stepwise process with the successive elimination of chlorines.

ChemInform Abstract: An Efficient and General Iron‐Catalyzed C—C Bond Activation with 1,3‐Dicarbonyl Units as a Leaving Groups.

AbstractDiones such as (I) undergo a novel FeCl3‐catalyzed C—C bond cleavage to release carbocations which are treated with reactive arenes to afford the products of electrophilic aromatic substitution.

An Efficient and General Iron‐Catalyzed CC Bond Activation with 1,3‐Dicarbonyl Units as a Leaving Groups

Diones such as (I) undergo a novel FeCl3-catalyzed C—C bond cleavage to release carbocations which are treated with reactive arenes to afford the products of electrophilic aromatic substitution.

Celite-Supported Reagents in Organic Synthesis: An Overview

The use of reagents supported on inorganic carriers is becoming increasingly more common due to their high efficiency, which is mainly caused by a combination of several factors: a) an increase in the effective surface area for reaction; b) the presence of pores which constrain both substrate and reactant, thus lowering the activation entropy of the reaction; c) a synergism (for displacement reactions) resulting from bringing electrophiles and nucleophiles into proximity. Thus, organic reactions can be carried out cleanly, rapidly and in high yield under mild conditions. In this context, the diatomaceous earth Celite has been successfully employed to support a plethora of reagents, ranging from alkali fluorides (which allow to attain high chemoselective (hetero) atom (N, O, S) functionalization protocols, as well as Michael additions, nucleophilic aromatic substitution or organotin waste product removal), to oxidant agents (such as silver carbonate or chromium trioxide, in order to promote mild oxidations), as well as dehydrating agents (such as DCC). The absence of any chemical reactivity of this support is compatible with high functionalized molecules, therefore constituting a suitable methodology to modulate the reactivity of the effective reagent. Furthermore, the application of Celite-supported enzymes is a well known strategy for performing regio and/or stereoselective biotransformations; in fact, this easy immobilization technique allows the preparation of highly stable and active biocatalysts for many synthetic applications. Thus, in this paper we will present an overview of the use of Celite-supported reagents, both organic molecules and biocatalysts, in organic chemistry and biotransformations. Keywords: Celite, supported reagents, chemoselectivity, fluorides, biotransformations, functionalization protocols, oxidant agents, dehydrating agents, Celite-supported enzymes, diatomite, acetonitrile, Potassium Fluoride, α-bromo-γ-butyrolactone, electrophilic reagent, Nucleophilic Aromatic Substitutions, Intramolecular Michael Additions, Phosphoramidates Synthesis, Montmorillonite, kieselgel, Cesium Fluoride, tetraalkyammonium fluorides, nucleophilic oxygen atoms, nucleophile, heteroaromatic thiols, 3,4-dihydropyrimidin-2-(1H)ones, β-diketoester enolate, 1,3-thiazolidin-4-ones, Aquaphilicity, Porcine pancreas, Candida rugosa, C. Cylindracea, Thermomyces lanuginosus, Humicola lanuginosa, Penicillium camembertii, P.cyclopium, Rhizopus javanicus, Mucor javanicus, Rhizomucor miehei, Rhizopus oryzae, R. javanicus, R. delemar, R. niveus, Candida antarctica B, Pseudomonas cepacia, Burkhloderia cepacia, Pseudomonas fluorescens, Chromobacterium viscosum, Bacillus thermocatenolatus

ChemInform Abstract: Ligand Effects on Dirhodium(II) Carbene Reactivities. Highly Effective Switching Between Competitive Carbenoid Transformations.

Carboxylate and carboxamide ligands of dirhodium(II) catalysts control chemoselectivity in competitive metal carbene transformations of diazo compounds. For competitive intramolecular cyclopropanation versus intramolecular aromatic substitution with 1-diazo-3-aryl-5-hexen-2-ones, use of Rh 2 (OAc) 4 results in the products from both transformations in nearly equal amounts, but dirhodium(II) perfluorobutyrate (Rh 2 (pfb) 4 ) provides only the aromatic substitution product while dirhodium(II) caprolactamate (Rh 2 (cap) 4 ) gives only the cyclopropanation product

A Novel Purification Method in Organic Synthesis Using Hydrogen Bonding

AbstractA new workup and purification method based on quadruple hydrogen‐bonding interactions is reported. Substrates containing a hydrogen‐bonding affinity tag – either directly connected or through a cleavable linker – were conveniently separated from a reaction mixture and purified using a resin containing self‐complementary affinity tags. Several Ugi products and nucleophilic aromatic substitution products were successfully purified by this hydrogen‐bonding‐based affinity‐separation protocol.(© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2007)

Destruction and Removal of PCBs in Waste Transformer Oil by a Chemical Dechlorination Process

A practical and efficient disposal of PCBs (polychlorinated biphenyls) in waste transformer oil by a chemical dechlorination process has been reported. The transformer oil containing commercial PCB mixtures (Aroclor 1242, 1254 and 1260) was treated by the required amounts of PEG 600 (polyethylene glycol 600), potassium hydroxide (KOH) and aluminum (Al), along with different reaction temperatures and times. The reaction of PEG with PCBs under basic condition produces arylpolyglycols, the products of nucleophilic aromatic substitution. The relative efficiencies of PCB treatment process were assessed in terms of destruction and removal efficiency (DRE, %). Under the experimental conditions of PEG600/KOH/Al/100 o C/2hr, average DRE of PCBs was approximately 78%, showing completely removal of PCBs containing 7-9 chlorines on two rings of biphenyl which appear later than PCB no. 183 (2,2',3,4,4',5',6-heptaCB) in retention time of GC/ECD. However, when increasing the reaction temperature and time to 150 o C and 240 min, average DRE of PCBs including the most toxic PCBs (PCB no. 77, 105, 118, 123 and 169) in PCB family reached 99.99% or better, with the exception of PCB no. 5 and 8 (2,3-diCB and 2,4'-diCB). In studying the reaction of PEG with PCBs, it confirmed that the process led to less chlorinated PCBs through a stepwise process with the successive elimination of chlorines. The process also permits complete recovery of treated transformer oil through simple segregating procedures.

Conjugate addition of aromatic amines to ethenetricarboxylates

The conjugate addition of amines is considered to be a useful reaction in synthetic organic chemistry. The reaction of reactive electrophilic olefins, ethenetricarboxylates, and aromatic amines with and without catalytic Lewis acids such as ZnCl 2 and ZnBr 2 at room temperature gave amine adducts in high yields. The products were converted to α-amino acid, dl-aspartic acid derivatives. Using Lewis acids such as Sc(OTf) 3 and Zn(OTf) 2 at higher temperature (40–80 °C), the reaction of ethenetricarboxylates and N-methylaniline gave an aromatic substitution product. A catalytic enantioselective conjugate addition using a chiral Lewis acid was also investigated. For example, the reaction of 1,1-diethyl 2- tert-butyl ethenetricarboxylate with N-methylaniline in the presence of chiral bisoxazoline-Cu(II) complex in THF at −20 °C for 17 h gave an amine adduct in 91% yield and 78% ee. On the other hand, the reaction with aniline and primary aniline derivatives gave adducts with almost no ee%.

Photoreactions of 1,2,4,5-benzenetetracarbonitrile with arylethenes—photo- olefin dimerization–aromatic substitution reactions

Abstract Irradiation of 1,2,4,5-tetracyanobenzene (TCNB) with styrene derivatives 1–4, respectively, leads to a photochemical olefin dimerization–aromatic substitution reaction to give the corresponding (2,4,5-tricyanophenyl)tetralin derivative (8, 12, 16, 17, and 20) as the main product. Further irradiation of the primary product with alkene results in substitution of the meta-CN group by another phenyltetralinyl to give the corresponding 4:1 (alkene–TCNB) product. According to the effect of the codonor (biphenyl) and salt (magnesium perchlorate) on reaction rate, the result of photoinduced reactions of TCNB with tetralin (6) and 1-phenyltetralin (7) and analysis of the known kinetic data for relevant processes in the cyanoarene–alkene reactions, the mechanism for the formation of the olefin dimerization–aromatic substitution products (such as 8) is proposed to involve radical pair combination of the alkene cyclodimer radical (the corresponding 4-phenyl-1-tetralinyl radical) with TCNB− followed by expulsion of a CN−. Photoreactions of TCNB with the alkene photocyclodimer (1-phenyltetralin) may also make minor contributions. Photoinduced reaction of TCNB with 1-phenylcyclohexene (5) takes a different pathway from 1–4 to afford the 1:1 (5–TCNB) primary product 21 by deprotonation of 5+ and radical pair combination with TCNB− followed by elimination of HCN.

Synthetic Utilization of Polynitro Aromatic Compounds. 5. Multi-Centered Reactivity Pattern in Reactions of 4,6-Dinitro-1,2-benzisothiazoles and -isothiazol-3(2H)-ones with C-, N-, O-, S-, and F-Nucleophiles

Reactions of 4,6-dinitro-1,2-benzisothiazoles, -isothiazol-3(2H)-ones, and -isothiazol-3(2H)-one-1-oxides with C-, N-, O-, S-, and F-nucleophiles give products of aromatic nucleophilic substitution of one or two nitro groups, vicarious substitution of the hydrogen atom H-7, or heterocyclic S-N bond cleavage depending on the structure of the starting compound and the nature of the nucleophile. These reactions provide a new synthetic approach to a family of biologically active benzisothiazol-3(2H)-ones based on 2,4,6-trinitrotoluene (TNT).