Quinones 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

Conversion to ortho- and para-quinones is by far the most common oxidation of phenols. Mercuric oxide or mercuric trifluoroacetate [583], lead dioxide [430], chromium trioxide [559], bromine [732], 2,3 dichloro-5,6-dicyano-/> benzoquinone (DDQ) [977], Fremy salt [487, 488, 489], and hydrogen peroxide in the presence of horseradish peroxidase [7958] are the most widely used oxidants (equations 310 and 311). 

A different approach for the construction of divergently linked donor-acceptor complexes was reported by D Souza.Hydroquinone-appended porphyrin 131 as a photodonor was prepared to associate with a quinone via double hydrogen bonding. Upon addition of 2,6-dichloro-3,5-dicyano-/ -benzoquinone, the fluorescence of zinc porphyrin was considerably quenched in benzonitrile. 

The oxidation (dehydrogenation) of the EDOT-dimer by quinones like chloro-anil or 2,3-dichloro-4,5-dicyano-benzoquinone (see Figure 5.17) presents a rapid and easy access to the bis-EDOT (BEDOT) 2,2 -di(3,4-ethylenedioxythiophene), ... 

Quinones, which become reduced to the corresponding hydroquinones. Two important quinones often used for aromatizations are chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone) and DDQ (2,3-dichloro-5,6-dicyano-l,4-ben-zoquinone). The latter is more reactive and can be used in cases where the substrate is difficult to dehydrogenate. It is likely that the mechanism involves a transfer of hydride to the quinone oxygen, followed by the transfer of a proton to the phenolate ion °... 

EPR techniques were used to show (Polyakov et al. 2001a) that one-electron transfer reactions occur between carotenoids and the quinones, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), and tetrachlorobenzoquinone (CA). A charge-transfer complex (CTC) is formed with a -values of 2.0066 and exists in equilibrium with an ion-radical pair (Car Q ). Increasing the temperature from 77 K gave rise to a new five-line signal with g=2.0052 and hyperfine couplings of 0.6 G due to the DDQ radical anions. At room temperature a stable radical with y=2.0049 was detected, its... 

With chlorinated quinones. New heterocycles containing 1,2-dihydro-imidazo [l,2- ]imidazol-3-one 405 or 1/7-imi-dazo[l,2- ]pyrazole moieties were obtained via charge-transfer interaction of creatinine or 3-aminopyrazole with some 7i-deficient compounds such as 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, 2,3,5,6-tetrachloro-l,4-benzoquinone, 2,3-dichloro- or 2,3-dicyano-1,4-naphthoquinone, and 3,4,5,6-tetrachloro-l,2-benzoquinone (Equation 183) C1996BSB159, 2001HC0541, 2000PS1>. 

Commercially available 2,3-dichloro-5,6-dicyano-l,4-benzo-quinone was employed. 1,6-Methano[10]annulene was obtained in equally good yields, when 2,3-dichloro-5,6-dicyano-l,4-benzoquinone, prepared by the method of Walker and Waugh,4 was utilized. 

General methods for o-quinones Benzoyl /-butyl nitroxide, 28 General methods for p-quinones Dicarbonylcyclopentadienylcobalt, 96 2,3-Dichloro-5,6-dicyano-1,4-benzoqui-none, 104 Squaric acid, 284 Benzoquinones... 

The key to the construction of the system is the choice of the quinone redox couple in the oil phase and the oil itself. The quinone compound must be reduced by Fe(II) ions, and the reduced form must be oxidized by bromine. These requirements indicate that the redox potential must be in the range between 0.77 and 1.07 V vs. NHE. After investigating of many redox compounds, we found that 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) dissolved in n-butyronitrile may be a good candidate for the system. DDQ has a largely positive redox potential because of its strong electron withdrawing substituents. 

Oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) of the thiourea 51, derived from dopamine, gave the 1,3-benzothiazepine 53 in quantitative yield via a facile J-based nucleophilic intramolecular addition to the intermediate o-quinone 52 (Equation 9) <2005OBC2387>. 

The phenolic hydroxyl and etherified benzyl alcohol group can be selectively oxidized by periodate [385] and 2,3-dichloro-5,6-dicyano-l, 4-benzoquinone (DDQ) [386], respectively. The periodate oxidation of guaiacyl and syringyl nuclei yields 0-quinones plus methanol and has been used to estimate the phenolic hydroxyl group content of lignin. DDQ oxidation has been applied to estimate the content of lignin-carbohydrate linkages [28]. 

The oxidation of ketones to enones via the reaction of their silyl enol ethers with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) has been suggested originally to proceed via allylic hydride abstraction [195-198]. A recent reinvestigation, however, [199] has established the intermediate formation of a substrate-quinone adduct 96 which was presumably formed from a geminate radical ion pair after electron transfer. Decomposition of the adduct then finally afforded the observed enone product 97. Recently, the critical role of solvent polarity in the formation of 97 from the PET reaction of 93 and chloranil has been identified by time-resolved spectroscopy [200]. 

When testosterone acetate is refluxed with 2,3-dichloro-5,6-dicyano-p-benzoquinone andp-toluenesulfonic acid in benzene for 5 h, a 60% yield of 6-dehydrotestosterone acetate is obtained [966]. The treatment of an-drost-4-ene-3,17-dione in dioxane with the same quinone and gaseous hydrogen chloride gives a 72% yield of androsta-4,6-diene-3,17-dione [966] (equation 30). 

Very selective oxidizing agents suitable for the conversion of primary alcohols into aldehydes are high-potential quinones such as tetrachloro-o-benzoquinone, tetrachloro-p-benzoqninone, and 2,3-dichloro-5,6-dicyano-p-benzoquinone [973]. Such dehydrogenations are carried out in chloroform, carbon tetrachloride, or ethanol, usually under very mild conditions at room temperature or in refluxing ether, and give fair to good yields (equation 216) [973]. 

A solution of 0.65 g (0.005 mol) of tetralin and 1.14 g (0.005 mol) of 2,3-dichloro-5,6-dicyano-p-benzoquinone in 5 mL of benzene is refluxed for 45 min, during which period the initidly red solution becomes colorless. A solution of an additional 1.14 g (0.005 mol) of the quinone in 2 mL of benzene is added, and the refluxing is continued for an additional 75 min. After dilution with light petroleum, the solution is filtered, passed through a column of alumina, and evaporated to give 0.42 g (70%) of naphthalene, mp 79-80 °C. The petroleum-insoluble residue yields 0.7 g (61%) of colorless 2,3-dichloro-5,6-dicyanohydroquinone, mp 263 °C (dec), after crystallization from aqueous ethanol. 

This high-potential quinone is second in effectiveness to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in the dehydrogenation of tetralin, acenaphthene, and dibenzyl in benzene at SO"." Kinetic studies are reported. The dehydrogenation of the 1,1-dimethyltetralin is attended with Wagner-Meerwein rearrangement ... 

A variety of organic compounds such as 2,3-dichloro-5,6-dicyano-p-quinone (DDQ) and related benzoquinones, m-chloroperbenzoic acid, or dioxirane have been utilized as oxidants in organic synthesis. This section will focus on the synthesis of natural products and related compounds using DDQ. 

Unsaturated esters can be formed from 1-siloxy-l-alkoxycyclopropanes in the reaction with a quinone, such as 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) or tetrachloro-l,4-ben-zoquinone, where ring-opened C —C and C —O bonded adducts are likely to be involved as intermediates formed via a single electron transfer mechanism. - Application to C — C bond... 

Dehydrogenation of pyrocatechol by silver oxide gives 0-benzoquinone.469 For preparation of amino-0-benzoquinones see Homer and Lang.470 Hydro-quinones are also dehydrogenated with success by lead tetraacetate.222 Further, 2,3-dichloro-5,6-dicyano-l,2-benzoquinone is obtained from the hydroquinone in 83% yield when a solution of the latter in 5% ethanolic hydrogen chloride is shaken with a mixture of Pb02 and benzene.471... 

Note that catechols (1,2-dihyroxybenzenes) are readily oxidized to o-quinones, l5 but the products are often sensitive to the electrophilic or nucleophilic species in the reaction medium. Catechol itself gives 125. Dimerization is as much a problem with catechols as with monophenols (see Table 3.4). The conversion of catechol to 125 used silver carbonate and it is noted that silver salts are the classical oxidation reagent for such transformations. Other reagent have been used to oxidize catechol derivatives, including ceric sulfate, lead tetraacetate, DDQ (2,3-dichloro-5,6-dicyano-l,4-benzoquinone), iodate, and periodate. ... 

Musgrave and Buchan developed a procedure for the preparation of triphenylene-l,4-quinones from 2,3-diaryl-l,4-benzoquinones using an acid-catalyzed intramolecular Scholl reaction. Using the 2,3-diaryl-1,4-benzoquinone 17, the AlCls-mediated cyclization occurred to afford a quinol intermediate that was then oxidized in the presence of FeCb to afford the triphenylenequinone 18 in moderate yield under mild reaction conditions. Inclusion of 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) as an oxidant has also been shown to increase the yield of the reaction up to 50%. 

The oxidative polymerization of diphenyl disulfide was carried out in the presence of a strong acid by electrolysis (198) and by reaction with Lewis acids such as SbCls (199-201) or quinones such as 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (202-205). VO catalysts such as vanadyl acetylacetonate with O2 have also been used for the oxidative polymerization (206-208), and the catalytic reaction mechanism involving four-electron reduction of O2 has been discussed (209-215). 

Quinones, as oxidation products of aromatic systems, are capable of being reduced back to aromatic systems and some quinones are used particularly for this purpose. For example, as shown in Scheme 6.79, 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ) can be used to oxidize 1,2,3,4-tetrahydronaphthalene (tetraUn, CioFli2) to naphthalene (CioHg) while it is reduced to the corresponding phenol, 2,3-dichloro-5,6-dicyanohydroquinone (DDQ H2). Further, while reduced to the same product, DDQ is also capable of oxidizing 1,3,5-cycloheptatriene to the corresponding, aromatic cycloheptatrienyl cation and, if the oxidation is carried out in perchloric acid, the perchlorate of the cation is an isolable salt (Scheme 6.79). 

We were able to show ° through esr and traping experiments, that the initiation of polymerization of vinyl ethers by 2,3-dichloro-556-dicyano-p-benzoquinone involved the quinone radical anion which coupled with the ether radical cation. 

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