- Catalytic Electrophilic Alkylation of p-Quinones through a Redox Chain Reaction
-
Allylation and benzylation of p-quinones was achieved through an unusual redox chain reaction. Mechanistic studies suggest that the existence of trace hydroquinone initiates a redox chain reaction that consists of a Lewis acid catalyzed Friedel–Crafts alkylation and a subsequent redox equilibrium that regenerates hydroquinone. The electrophiles could be various allylic and benzylic esters. The addition of Hantzsch ester as an initiator improves the efficiency of the reaction.
- Xu, Xiao-Long,Li, Zhi
-
supporting information
p. 8196 - 8200
(2017/06/30)
-
- Involvement of semiquinone radicals in the in vitro cytotoxicity of cigarette mainstream smoke
-
Free radicals in cigarette smoke have attracted a great deal of attention because they are hypothesized to be responsible in part for several of the pathologies related to smoking. Hydroquinone, catechol, and their methyl-substituted derivatives are abundant in the particulate phase of cigarette smoke, and they are known precursors of semiquinone radicals. In this study, the in vitro cytotoxicity of these dihydroxybenzenes was determined using the neutral red uptake (NRU) assay, and their radical-forming capacity was determined by electron paramagnetic resonance (EPR). All of the dihydroxybenzenes studied were found to generate appreciable amounts of semiquinone radicals when dissolved in the cell culture medium employed in the NRU assay. Hydroquinone exhibited by far the highest capacity to form semiquinone radicals at physiological pH, even though it is not the most cytotoxic dihydroxybenzene. Methyl-substituted dihydroxybenzenes were found to be more cytotoxic than either hydroquinone or catechol. The formation of semiquinone radicals via auto-oxidation of the dihydroxybenzenes was found to be dependent on the reduction potential of the corresponding quinone/semiquinone radical redox couple. The capacity to generate semiquinone radicals was found to be insufficient to explain the variance in the cytotoxicity among the dihydroxybenzenes in our study; consequently, other mechanisms of toxicity must also be involved. The observed interactions between 2,6-dimethylhydroquinone and hydroquinone in the cytotoxicity assay and EPR analysis suggest that care needs to be taken when the bioactivity of cigarette smoke constituents is evaluated, i.e., the effect of the cigarette smoke complex matrix on the activity of the single constituent studied must be taken into consideration.
- Chouchane, Salem,Wooten, Jan B.,Tewes, Franz J.,Wittig, Arno,Mueller, Boris P.,Veltel, Detlef,Diekmann, Joerg
-
p. 1602 - 1610
(2008/12/22)
-
- Preparation of 1,4-hydrobenzoquinones by the PCC/SiO2-promoted double oxidation of 3-cyclohexene-1,2-diols
-
The PCC/SiO2-promoted double oxidation of 3-cyclohexene-1,2- diols, which were easily prepared by the two-step sequence of α-hydroxylation of various conjugated cyclohexenones and the subsequent nucleophilic carbonyl addition of alkyl anions, produced diversely substituted 1,4-hydrobenzoquinones. The Royal Society of Chemistry 2005.
- Kim, Hee Jin,Koo, Sangho
-
p. 3479 - 3481
(2007/10/03)
-
- Comparative pulse radiolysis studies of alkyl- and methoxy-substituted semiquinones formed from quinones and hydroquinones
-
Absorption spectra and rate constants for the disproportionate of 12 alkyl- and methoxy-substituted semiquinone anion free radicals (Q?-) produced by the one-electron reduction (using CO2?- as a reductant) of 1,4-benzoquinones and 1,4-naphthoquinone (Q) as well the oxidation (using N3? as an oxidant) of the corresponding hydroquinones (QH2) were determined by pulse radiolysis in 50 mM sodium phosphate buffer, pH 7.40 at room temperature. Both spectral and kinetic characteristics of Q?- only moderately depended on whether Q?- was produced from Q or QH2. Spectra of benzosemiquinones display two peaks with maximum at 310-320 nm and ca. 430 nm with the ratio of about 2-2.5. Molar absorption coefficients were determined. Rate constants for Q?- disproportionation (2k1) were correlated with the nature of substituents. While 2k1 was scarcely affected by methyl substitution, Q?- containing isopropyl, tert-butyl and methoxy substituents were visibly more stable than non-substituted and methyl-substituted Q?-.
- Roginsky, Vitaly A.,Pisarenko, Leonid M.,Bors, Wolf,Michel, Christa,Saran, Manfred
-
p. 1835 - 1840
(2007/10/03)
-
- Process for the preparation of aromatic polyhydroxy compounds
-
The present invention relates to a process for the preparation of aromatic polyhydroxy compounds, by reacting an aromatic hydroxyaldehyde with hydrogen peroxide, with or without the addition of a base, in the presence of a nitrile R--CN, in which R is an alkyl radical having 1 to 4 carbon atoms or a phenyl radical, which is unsubstituted or substituted by one or more alkyl groups.
- -
-
-
- Synthesis of plastoquinone derivatives with different structures of the side chain
-
Two schemes for the synthesis of plastoquinone derivatives with ω-substituted alkyl side chains have been developed, based on radical alkylation of 2,3-dimethyl-1,4-benzoquinone with ω-substituted carboxylic and/or dicarboxylic acids in the presence of S2O82- and Ag+.In Scheme 1, radical alkylation of 2,3-dimethyl-1,4-benzoquinone with 11-bromoundecanoic acid, in the presence of (NH4)2S2O8 and AgNO3, gave 2,3-dimethyl-5-(10-bromodecyl)-1,4-benzoquinone, which, after hydration, gave 2,3-dimethyl-5-(10-hydroxydecyl)-1,4-benzoquinone.Esterification of 2,3-dimethyl-5-(10-hydroxydecyl)-1,4-benzoquinone with different acyl chlorides gave 2,3-dimethyl-5-(10-acyloxydecyl)-1,4-benzoquinone.In Scheme 2, radical alkylation of 2,3-dimethyl-1,4-benzoquinone with adipic acid, in the presence of K2S2O8 and AgNO3, gave 2,3-dimethyl-5-(4-carboxybutyl)-1,4-benzoquinone, which was converted to 2,3-dimethyl-5--1,4-benzoquinone by esterification with different alcohols in the presence of dicyclohexylcarbodiimide. 2,3-Dimethyl-5-(8-carboxyoctyl)-1,4-benzoquinone and 2,3-dimethyl-5--1,4-benzoquinone were similarly synthesized from 2,3-dimethyl-1,4-benzoquinone and sebacic acid.Plastoquinone derivatives having different kinds of double bonds in the side chain with and without a 6-methyl group were synthesized from 2,3,5-trimethyl-1,4-benzoquinone and 2,3-dimethyl-1,4-benzoquinone by successive reactions with (1) NaBH4; (2) KHSO4, different kinds of allylic alcohols; (3) Ag2O.The allylic alcohols were prepared from their corresponding aldehydes by reduction with NaBH4. 2,3,6-Trimethyl-1,4-benzoquinone by radical methylation with acetic acids in the presence of K2S2O8 + AgNO3.
- Liu, Benli,Gu, Lianquan,Zhang, Jingling
-
p. 104 - 110
(2007/10/02)
-
- Mechanism of the Oxidation of NADH by Quinones. Energetics of One-Electron and Hydride Routes
-
The kinetics of NADH oxidation by 7 o-benzoquinones and 14 p-benzoquinones were studied by using buffered aqueous solutions and UV/vis spectroscopy.For each quinone the rate law was first order in NADH and first order in quinone.The rate constants varied from 0.0745 to 9220 M-1s-1.Variation of the pH from 6 to 8 gave no change in rate.The use of 4-D and 4,4-D2NADH revealed kinetic isotope effects.The dideutero data gave kH/kD in the range 1.6-3.1 for p-quinones and 4.2 for 3,5-di-tert-butyl-o-quinone.When p-quinones were used, the log k was a linear function of Eo for the quinone/hydroquinone monoanion (Q/QH(1-)) couple with a slope of 16.9 V-1. o-Quinones reacted about 100 times more rapidly, but the same linear relationship with a slope of 16.4 V-1 was observed.Comparisons to data for one-electron-transfer reactions indicate that such mechanisms are not involved.A hydride-transfer mechanism accommodates all the data, and rate-limiting hydrogen atom transfer followed by electron transfer cannot be ruled out.
- Carlson, Brian W.,Miller, Larry L.
-
p. 479 - 485
(2007/10/02)
-
- Preparation of 4,4-dihydroxydiphenyl ethers
-
Substituted and unsubstituted 1,4-dihydroxybenzenes are reacted in the presence of a cation exchange resin catalyst and an inert solvent to form the corresponding 4,4'-dihydroxydiphenyl ethers.
- -
-
-
- REACTIONS OF ORGANOLITHIUM REAGENTS WITH p-BENZOQUINONES AND CYCLOHEXADIENONS, SYNTHESIS OF 4-ALKYL-4-HYDROXYCYCLOHEXA-2,5-DIEN-1-ONES AND 1,4-DIALKYLCYCLOHEXA-2,5-DIENE-1,4-DIOLS.
-
Addition of organolithium reagents to p-benzoquinones in ether gives the corresponding 4-alkyl-4-hydroxycyclohexa-2,5-dien-1-ones.Addition of excess of the reagent to the p-benzoquinones, or to the 4-alkyl-4-hydroxycyclohexa-3,5-dien-1-ones, in tetrahydrofuran, gives the corresponding dialkylcyclohexa-2,5-diene-1,4-diols.
- Fischer, A.,Henderson, N.
-
p. 701 - 704
(2007/10/02)
-
- Allylation of Quinones with Allyltin Reagents
-
Lewis acid (BF3) catalyzed allylation of quinones with allyl- (2a), 2-methyl-2-propenyl- (2b), trans-2-butenyl- (2c,d), 3-methyl-2-butenyl- (2e,f), and trans-cinnamyltrialkyltin (2g) gives the corresponding allylhydroquinones with high regioselectivity.Vitamin K2(5) (7) and coenzyme Q1 (9) were prepared in yields of 78 and 75percent, respectively.These reactions appear to proceed through allylquinol intermediates which undergo rearrangement under the influence of BF3.The success of this synthesis of vitamin K2(5) and coenzyme Q1 depends on the fact that the reaction of 3-methyl-2-butenyltin with quinones occurs at the α carbon of the allylic system.
- Naruta, Yoshinori
-
p. 3774 - 3783
(2007/10/02)
-
