An intriguing reaction of 4-hydroxycoumarins with 2,3-dichloro-5,6-dicyanobenzoquinone

An intriguing reaction of 4-hydroxycoumarins with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) occurred in the presence of catalytic acetic acid in ethanol at reflux with the products being obtained in high yields.     

Reaction of 4,5-dichloro-3-trichloromethylisothiazole with heterocyclic amines

4,5-Dichloro-3-trichloromethylisothiazole reacted with piperidine, morpholine, pyrrolidine, and piperazine in DMF to give 81–96% of the corresponding 5-amino-4-chloro-3-trichloromethylisothiazoles as a result of selective nucleophilic replacement of the 5-chlorine atom. Acylation of 4-chloro-5-(piperazin-1-yl)-3-trichloromethylisothiazole with acetyl chloride gave 4-chloro-5-(4-acetylpiperazin-1-yl)-3-trichloromethyl-isothiazole.     

The use of 2,3-dichloro-5,6-dicyano-p-benzoquinone for the spectrophotometric determination of some cardiovascular drugs

Some basic cardiovascular drugs containing secondary or tertiary amino groups are determined spectrophotometrically. The method is simple and sensitive; it is based on the interaction of the drugs, as n-electron donors, with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as a pi-acceptor. The highly coloured radical anion exhibits maximum absorption at 460 nm. The drugs determined are pindolol, dipyridamole, hydralazine hydrochloride, quinidine sulphate, prenylamine lactate and tolazoline hydrochloride. Beer's law is obeyed for these drugs. The procedure is sensitive enough to permit unit dose assay of the individual drugs in their pharmaceutical formulations. The assay results are in accord with the pharmacopoeial assay results.     

Novel synthesis of enamines by iridium-catalyzed dehydrogenation of tertiary amines

A novel route to enamines is reported, the dehydrogenation of tertiary amines catalyzed by a "pincer-ligated" iridium catalyst.     

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.     

Reaction of methyl-substituted pyrylium salts with tertiary amines

2,4,6-Trimethylpyrylium perchlorate reacts with heterocyclic compounds containing apyridine nitrogen atom and having basicities higher than 9 pK_a units (in acetonitrile) through a step involving the formation of a methylenepyran. 4-Methyl-2,6-diphenyl- and 2-methyl-4,6-diphenylpyrylium perchlorates react with benzimidazole to give 1,2-ethanediylidenebispyrans. Methyl-substituted pyrylium salts react with 2,6-diphenylpyrylium and flavylium perchlorates in the presence of benzimidazole to give methylidynecyanines and with acetic anhydride to give trimethylidynecyanines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1484–1489, November, 1976.     

Reaction of dichlorocarbene with 2,3-dihydro-5,6-dimethyl-1,4-oxathiin and 2,3-dihydro-5,6-dimethyl-1,4-dithiin

Dichlorocarbene, generated from ethyl trichloroacetate and sodium ethoxide, reacts with 2,3-dimethyl-5,6-dihydro-1,4-oxathiin to give 7,7-dichloro-1,6-dimethyl-2-oxa-5-thiabicyclo[4,1,0]heptane, and with 2,3-dimethyl-5,6-dihydro-1,4-dithiin to give 6-chloro-2,3-dihydro-7-methyl 5-methylene-5(H)-1,4-dithiepin. Both products were oxidised to the corresponding sulfone.     

Reaction of N-phenylsulfonylbenzoxazolone with some amines

The reaction of N-phenylsulfonylbenzoxazolone with amines was investigated in order to study the mechanism of the reaction between aryloxazolones and amines. The sulfonyl group accelerates the reaction considerably. The structure of 2-(phenylsulfamido)phenyl esters of the corresponding N-substituted carbamic acids was assigned to the products on the basis of the IR spectra and alternative synthesis. The reaction with secondary aliphatic amines (dimethyl- and diethylamine)proceeds considerably more slowly and results in the formation of 2-(phenylsulfamido)phenol.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1333–1336, October, 1971.     

Spectroscopic studies on the interaction of cilostazole with iodine and 2,3-dichloro-5,6-dicyanobenzoquinone

Lanthanide sensitized luminescence and chemiluminescence (CL) are of great importance because of the unique spectral properties, such as long lifetime, large Stokes shifts, and narrow emission bands characteristic to lanthanide ions (Ln³⁺). With the fluoroquinolone (FQ) compounds including enoxacin (ENX), norfloxacin (NFLX), lomefloxacin (LMFX), fleroxacin (FLRX), ofloxacin (OFLX), rufloxacin (RFX), gatifloxacin (GFLX) and sparfloxacin (SPFX), the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes have been investigated in this contribution. Ce⁴⁺–SO₃²⁻ in acidic conditions was taken as the CL system and sensitized CL intensities of Tb³⁺–FQ and Eu³⁺–FQ complexes were determined by flow-injection analysis. The luminescence and CL spectra of Tb³⁺–FQ complexes show characteristic peaks of Tb³⁺ at 490 nm, 545 nm, 585 nm and 620 nm. Complexes of Tb³⁺–ENX, Tb³⁺–NFLX, Tb³⁺–LMFX and Tb³⁺–FLRX display relatively strong emission intensity compared with Tb³⁺–OFLX, Tb³⁺–RFX, Tb³⁺–GFLX and Tb³⁺–SPFX. Quite weak peaks with unique characters of Eu³⁺ at 590 nm and 617 nm appear in the luminescence and CL spectra of Eu³⁺–ENX, but no notable sensitized luminescence and CL of Eu³⁺ could be observed when Eu³⁺ is added into other FQ. The distinct differences on emission intensity of Tb³⁺–FQ and Eu³⁺–FQ might originate from the different energy gap between the triplet levels of FQ and the excited levels of the Ln³⁺. The different sensitized luminescence and CL signals among Tb³⁺–FQ complexes could be attributed to different optical properties and substituents of these FQ compounds. The detailed mechanism involved in the luminescence and CL properties of Tb³⁺–FQ and Eu³⁺–FQ complexes has been investigated by analyzing the luminescence and CL spectra, quantum yields, and theoretical calculation results.     

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.     

Spectrophotometric titration of phenothiazines using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

A specific Spectrophotometric titration method is described for the micro-determination of some phenothiazine derivatives in strong orthophosphoric acid medium using the -acceptor 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as a mild oxidizing titrant. The wavelengths of maximum absorption of the formed phenothiazonium cation radicals are 500, 515, 530, 533 and 650 nm for trifluoperazine dihydrochloride, promethazine hydrochloride, prochlorperazine dimaleate, chlorpromazine hydrochloride and thiethylperazine dihydrochloride, respectively. Quantitative recoveries are reported for pure drugs and their dosage forms. The method is simple and specific for determining phenothiazine derivatives in presence of their induced degraded oxidation products.     

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]pyrazines from 2,3-dichloro-5,6-dicyanopyrazine with 2-aminopyridines

Novel synthesis of the title compounds by the facile cyclization between 2,3-dichloro-5,6-dicyanopyrazine and various 2-aminopyridines under relatively mild conditions is described. The reactivity depended on the basicity of 2-aminopyridines.     

Solvent effect on the charge transfer complex of oxatomide with 2,3-dichloro-5,6-dicyanobenzoquinone

The charge transfer complex (CT-complex) between oxatomide drug and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was studied spectrophotometrically in 10 solvents at different temperatures. The donor oxatomide is found to form stable 1:1 stoichiometric complex with DDQ and the stoichiometry was unaffected by change in polarity of the solvent studied. The DeltaH degrees, DeltaS degrees and DeltaG degrees values are all negative, so the studied complex is reasonably stable and exothermic in nature. The ionization potential of the drug was determined using the CT-absorption bands of the complex in all the solvents. The dissociation energy of the charge transfer excited state for the CT-complex in different solvents was also determined and is found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the nature of the solvent.     

Oxidative transformation of the natural lignan hydroxymatairesinol with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

The oxidative transformation of the two isomers of the natural lignan hydroxymatairesinol from Norway Spruce (Picea abies) by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), has been studied. Significant differences in the outcome of the reactions were observed when the pure isomers of hydroxymatairesinol were reacted with DDQ under the same conditions. The different stereoelectronic effects in the two isomers as well as their conformational structures seem to determine the site of reaction, which results in different reaction products. Several products were identified by GC-MS and NMR spectroscopy. Oxomatairesinol was obtained in a yield of 25%.     

Access to chiral tertiary amines via the iridium-catalyzed asymmetric hydrogenation of enamines

The asymmetric hydrogenation of N,N-dialkyl and N-alkyl-N-aryl enamines to chiral tertiary amines was studied. All the N,P-ligated iridium complexes investigated were active catalysts for the reaction, but only those with bicycle-supported oxazoline-phosphine ligands gave reasonable stereoinduction. The best catalyst produced a range of chiral tertiary amines in up to 87% ee.     

Reaction of some amines with unsaturated N-acylbenzoxazolones

It is shown that the addition of aniline proceeds at the carbon-carbon double bond of N-acryloyl-, N-chloroacryloyl-, and N-methylacryloylbenzoxazolones. The basicity of the amine has a substantial effect on the course of the reaction with various amines. Transamidation of the acryloyl residue occurs with strongly basic amines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1044–1048, August, 1974.     

Charge-transfer interaction of aromatic thiols with 2,3-dichloro-5,6-dicyano-p-benzoquinone: spectral and quantum mechanical studies

Charge-transfer (CT) complexes formed between aromatic thiol donors (thiophenol (TP), benzene-1,4-dithiol (BDT), p-aminothiophenol (ATP), p-hydroxythiophenol (HTP), and p-toluenethiol (TTP)) and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) as an acceptor were studied spectrophotometrically in dichloromethane. Addition of aromatic thiols in dichloromethane to DDQ leads to the formation of colored solutions that exhibit a very broad absorption band in the range 440-800 nm and a band in the region 300-400 nm. On the basis of the energies of LUMO and HOMO from quantum mechanical calculations, the broad band observed in the visible region was assigned to the pi*(a2) <-- pi(b1) transition and a band observed between 300 and 400 nm was assigned to the pi*(a2) <-- pi(a2) transition. The solid CT complexes of aromatic thiols and DDQ were prepared and characterized by FT-IR spectroscopy. The stoichiometry of the CT complexes was determined by Job's continuous variation method. The association constant (KCT), molar extinction coefficient (epsilon), oscillator strength (f), and transition dipole moment (micro) values were calculated from the electronic spectra. The vertical ionization potentials (ID) of the donors were calculated from their corresponding lambdaCT. Quantum mechanical (QM) calculations were performed to determine the ionization potential and the energies of the highest occupied molecular orbital (HOMO) of donors and lowest unoccupied molecular orbital (LUMO) of an acceptor.