Deprotection of benzyl ethers using 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) under photoirradiation

The deprotection of benzyl ethers was effectively realized in the presence of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in MeCN under photoirradiation using a long wavelength UV light.     

Stereochemistry of Dehydrogenation of 1,4,-Cyclohexadiene with 2,3-Dichloro-5,6-dicyano-p-benzoquinone

cis- and trans-(3,6-D₂)-1,4-cyclohexadienes 1a and 1b have been synthesized from cis-3,4-dichlorocyclobutene (5). Aromatization to benzene with DDQ is cis-stereospecific with an uncertainty of 5%. This result is discussed in relation to concerted or stepwise mechanisms for aromatization of 1,4-dihydroaromatics with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ).     

Metal-free oxidative aromatization of 2-aryloxycyclohex-2-en-1-ones to 2-aryloxyphenols using DDQ/Amberlyst-15

Efficient metal-free oxidative aromatization of 2-aryloxycyclohex-2-en-1-ones was achieved by a combination of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and Amberlyst-15. The conditions for oxidative aromatization are mild and applicable for a variety of substrates, and Amberlyst-15 can be successfully recovered and recycled.     

Molecular compounds of dichloro-p-benzoquinone derivatives with hydroxy aromatic Schiff's bases

The molecular complexes of some hydroxy aromatic Schiff's bases with 2,3-dichloro-5,6-dicyano-p-benzoquinone and chloranilic acid are prepared and investigated using electronic absorption, i.r. and ¹H-NMR spectroscopy. Molecular compounds with the former reagent are formed through charge transfer while those with chloranilic acid are formed through proton and electron transfer.     

Synthesis of aromatic polyesters and polyamides by alternating copolymerizations of 1,4-dicarbonyl-1,4-dihydronaphthalene with bezoquinones and benzoquinone diimines

1,4-Dicarbonyl-1,4-dihydronaphthalene ( 1 ) was synthesized by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride with triethylamine and obtained as its very dilute solution, but it easily polymerized in the concentration as high as 0.1 mol/L to give its polymer. 1 generated in situ by the dehydrochlorination reaction of 1,4-dihydronaphthalene-1,4-dicarbonyl chloride in a deoxygenated toluene polymerized alternatingly with benzoquinones such as 2-dodecylthio-p-benzoquinone, 2,5-di(tert-butyl)-p-benzoquinone, p-benzoquinone, and 2,3-dichloro-5,6-dicyano-p-benzoquinone, and with benzoquinone diimines such as N,N′-diethoxycarbonyl-p-benzoquinone diimine, N,N′-dibenzoyl-p-benzoquinone diimine, and N,N′-diphenyl-p-benzoquinone diimine to give aromatic polyesters and polyamides, respectively. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1929–1936, 1998     

Oxidation of styrene by 2,3-dichloro-5,6-dicyano-p-benzoquinone

Styrene is oxidized by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), affording hydroquinone mono(2-phenylethyl) ether. Kinetic studies (50°C in CHCl₃) show that the reaction is faster under N₂ than under air and takes placevia intramolecular H-atom transfer within the 1:1 and 1:2 DDQ-styrene charge-transfer complexes. The semiquinone radical intermediate is reoxidized to DDQ by O₂ when the latter is present, therefore, the apparent rate of DDQ reduction is lower. Stability constants of the CT-complexes and kinetic parameters for the oxidation are reported.     

DDQ-promoted direct C–H amination of ethers with N-alkoxyamides under visible-light irradiation and metal-free conditions

A C(sp³)–N bond forming reaction between N-alkoxyamides and simple ethers has been developed. In the presence of commercially available 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), a variety of N-methoxyamides and ethers undergo this transformation smoothly to deliver the corresponding products in good yields under visible-light irradiation and metal-free conditions at room temperature.     

Polymerization and oxidation of pyrrole by organic electron acceptors

Simultaneous chemical polymerization and oxidation of pyrrole have been initiated by organic electron acceptors, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetrachloro-o-benzoquinone(chloranil). The polypyrrole (PPY) complexes so produced are semiconductive and granular in nature. For the PPY–DDQ and PPY–chloranil complexes obtained from bulk polymerization, the respective electrical conductivities (σ) are of the order of 10^?1 and 10^?3 ohm^?1 cm^?1. However, σ is substantially lower for the complexes prepared in solvent media. Both complexes are relatively stable in the atmosphere. Thin uniform films of the PPY–organic acceptor complexes have also been synthesized on SnO₂ electrode by electrochemical polymerization in acetonitrile. The physicochemical properties of the PPY–organic acceptor complexes prepared chemically under the various experimental conditions are examined in detail.     

A spectrophotometric study of charge transfer complexes of thianthrene

The spectrophotometric properties of thianthrene with iodine and tetracyanoethylene at 24°C in different solvents such as cyclohexane, carbon tetrachloride, chloroform, methylene chloride and 1,2-dichloroethane are found to depend on the solvent. In addition, the charge transfer complexes of thianthrene with p-chloranil and 2,3-dichloro-5,6-dicyano-p-benzoquinone at 24°C in methylene chloride solvent were studied, also spectrophotometrically. The spectral data, the equilibrium parameters and the dissociation energy of the excited charge transfer complexes were determined. The role of the electron donor and the electron acceptor structure on the formation and stability of the charge transfer complexes was discussed.     

Charge transfer molecular complexes of arylidene anthranilic acid derivatives with π-electron acceptors

X-Benzylidenesanthranilic acid molecular complexes with π-acceptors, tetracyanoethylene, 2,3-dichloro-5,6-dicyano-p-benzoquinone and chloranil, have been studied. The intramolecular hydrogen bonding that exists in such compounds greatly inhibits the transition of the nitrogen azomethine n-electrons. The formation constant values and molar extinction coefficients of the p-dimethyl-aminobenzylidenean-thranilic acid-DDQ CT complexes have been determined in CH₂Cl₂, C₂H₄Cl₂ and CHCl₃ in the temperature range 10–30°C. Such CT complexes are of strong n-π type.     

Transfer hydrogenation and transfer hydrogenolysis—21 : Dehydrogenation of alcohols by quinones

Dehydrogenation of benzyl-type alcohols and hydroaromatic compounds by 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and tetrachloro-p-benzoquinone were examined, and the hydrogen transfer from 1-phenyl-1-propanol to DDQ was investigated in detail. The yield of the propiophenone increased when solvents which would be expected to increase the concentration of the charge transfer complex between the alcohol and DDQ were used. Initial rates of the reaction in dioxane were proportional to the concentration of the hydrogen donor and that of the hydrogen acceptor. In the dehydrogenation of several para- or meta-substituted 1-phenyl-1-propanols at 60°, ?3.30 was obtained as a value of reaction constant. Relative rates of the reaction of PhCH(OH)Et, PhCH(OD)Et, PhCD(OH)Et, and PhCD(OD)Et were 8.9,9.1,1.0 and 1, respectively. This result suggests that the transfer of the H atom attached to the α-carbon of the alcohol is the rate-determining step. This and some other results support a two-step ionic mechanism for the dehydrogenation of alcohols.     

XPS studies of charge transfer interactions in some polyphenylacetylene-electron acceptor systems

X-ray photoelectron spectroscopy (XPS) studies have been performed on charge transfer complexes of trans-polyphenylacetylene (PPA). The acceptors used included halogens, such as I₂ and Br₂, and organic electron acceptors, such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), chloranil, fluoranil, and 7,7,8,8-tetracyano-p-quinodimethane (TCNQ). Incomplete and relatively weak charge transfer interactions were observed in most of the complexes. These help to account for the relatively low conductivity levels observed in most of the PPA complexes when compared with the corresponding complexes of other conjugated polymers. PPA has also been found to interact with molecular oxygen to some extent in solution. In complexes involving O₂, Br₂, and fluoranil, XPS data suggest that the charge transfer interaction may have proceeded further than the pure formation of molecular charge transfer complexes.     

Cyclisation of Ortho -Cyclohexenyl Phenols via Epoxidation #

A number of ortho -cyclohexenyl phenols 2(a–i) have been cyclised by treatment with one equivalent of m-chloroper-oxybenzoic acid in refluxing benzene for 4 h to furnish linearly fused 1-hydroxy-1,2,3,4,4a,9a-hexahydrodibenzofurans 3(a–i) (70–80%) and bicyclic 3-hydroxy-1,3-ethanochromans 4(a–f) (10–20%). Products 3(a–i) were oxidised with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (excess) in refluxing dry xylene for 6 h to give 2,3-dihydrodibenzofuran-1 (2H)-ones 6(a–i) (85–95%).

     

Charge transfer interactions in polyphenylacetylene-electron acceptor systems

Charge transfer (CT) interaction of polyphenylacetylene (PPA) with iodine, arsenic pentafluoride and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) in solution is associated with the formation of broad CT bands extending beyond the absorption edge of the polymer into the near infra-red and with a substantial loss of the polymer's effective conjugation. For PPA-I₂ and PPA-DDQ in dilute solutions and at low doping levels, the 1:1 CT complex is susceptible to a Benesi-Hildebrand analysis. The microstructure of the polymer has a pronounced effect on the observed interaction rates and equilibrium constants. At high acceptor loadings, there are complicated time-dependent equilibria involving several complexes of different stoichiometry. The role of the CT state in this electroactive polymer is discussed in the context of a band-like model.     

Istope effects in aromatization of 1,4-dihydrobenzene and 1,4-dihydronaphthalene with quinones

Aromatization of 1,4-dihydronaphthalene with 2,3-dichloro-5,6-p-benzoquinone or chloranil is accompanied with kinetic isotope effects of 9.9 and 8.0 respectively.     

Alternating copolymerization of 2,3-dichloro-5,6-dicyano-p-benzoquinone with styrene and polymerization behavior with vinyloxy compounds

2,3-Dichloro-5,6-dicyano-p-benzoquinone (DDQ) was found to copolymerize alternatingly with styrene (St). DDQ–isobutyl vinyl ether and DDQ–2-chloroethyl vinyl ether systems gave homopolymers of vinyl ethers, while DDQ–phenyl vinyl ether and DDQ–vinyl acetate systems gave oligomers containing both monomer units. In the terpolymerization of DDQ, p-chloranil (pCA), and St, terpolymers obtained were found to have about 50 mole % of St units regardless of monomer feed ratio and DDQ was incorporated much more rapidly into the terpolymer than pCA. The difference in the reactivity of the acceptor monomers could be attributed to that in their electron-accepting character.     

Stereospecific functionalization of the heterocyclic ring systems of flavan-3-OL and [4,8]-biflavan-3-OL derivatives with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)

Efficient stereospecific 4-methoxylation of both 2,3-trans- and 2,3-cis-flavan-3-ol methyl ethers with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) in CHCl₃-MeOH solution is of both synthetic and degradative significance in oligomeric flavanoid chemistry.     

Chemical interactions between 2-mercaptobenzazoles and π-acceptors

Summary 2-Mercaptobenzazoles (1a–c) interact with several -acceptors such as tetracyanoethylene (TCNE) 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,3,5,6-tetrachloro-1,4-benzoquinone (CHL) dicyanomethyleneindane-1,3-dione (CNIND), 2,3-dicyano-1,4-naphthoquinone (DCNQ), 9-dicyanomethylene-2,4,7-trinitrofluorene (DTF), and 2,3-dichloro-1,4-naphthoquinone (DCHNQ)via the formation of charge-transfer (CT) complexes to yield various heterocyclic compounds.

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Chemische Wechselwirkungen zwischen 2-Mercaptobenzazolen und -Akzeptoren

Zusammenfassung Die 2-Mercaptobenzazole1a–c reagieren mit verschiedenen -Akzeptoren wie Tetracyanoethylen (TCNE), 2,3-Dichlor-5,6-dicyano-1,4-benzochinon (DDQ), 2,3,5,6-Tetrachlor-1,4-benzochinon (CHL), Dicyanomethylenindan-1,3-dion (CNIND), 2,3-Dicyano-1,4-naphthochinon (DCNQ), 9-Dicyanomethylen-2,4,7-trinitrofluoren (DTF) und 2,3-Dichlor-1,4-naphthochinon (DCHNQ) unter Ausbildung von charge transfer — Komplexen (CT) zu heterocyclischen Verbindungen.

     

Charge transfer interactions in some poly[[o-(trimethylsilyl)phenyl] acetylene]-acceptor complexes

Charge transfer (CT) interactions between poly[[o-(trimethylsilyl)phenyl]acetylene] or poly(o-Me₃SiPA) and some electron acceptors were studied by ultraviolet-visible and infrared absorption spectroscopy and by x-ray photoelectron spectroscopy, (XPS). The electron acceptors used included iodine, bromine, o-chloranil, o-bromanil, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and tetracyanoethylene (TCNE). Varying degrees of CT interactions were observed in all of the polymer/acceptor complexes studied. The electrical conductivities σ of the organic acceptor complexes exhibited a strong acceptor concentration dependence at low acceptor levels, with the DDQ complex exhibiting the highest σ. The extent of CT and the redistribution of charges resulting from the CT in all the complexes were revealed by XPS. The poly (o-Me₃SiPA)/I₂ complex film lost iodine spontaneously while more than half of the bromine in the poly (o-Me₃SiPA)/Br₂ complex existed as covalently bonded bromine, even at low halogen loading.     

Synthesis,Spectroscopic and Computational Studies of Charge-Transfer Complexation Between 4-Aminoaniline and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

A charge-transfer (CT) complex that forms from the reaction of the donor 4-amino aniline (4AA) and the π-acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) have been studied and characterized experimentally and as well as theoretically at room temperature. The experimental work includes the application of UV–visible spectroscopy to identify the CT band of the CT-complex. The composition of the complex has been investigated using spectrophotometric titration and Job’s method of continuous variation and found to be 1:1. Furthermore, to calculate the formation constant and molar extinction coefficient, we have used the Benesi–Hildebrand equation. Infrared, ¹H NMR, ¹³C NMR and mass spectral studies were used to characterize and confirm the formation of the CT-complex. The experimental studies were supported by quantum chemical simulations using density functional theory. The computational analysis of molecular geometry, Mulliken charges, and molecular electrostatic potential surfaces of reactants and complexes are helpful in assigning the CT route. The C=O bond length of DDQ increased upon complexation with 4AA. We have also observed that a substantial amount of charge has been transferred from 4AA to DDQ in the process of complexation. An excellent consistency has been achieved between experimental and theoretical results.