Quinones aromatization

One-electron reduction of a-dicarbonyl compounds gives radical anions known as setnidiones. Closely related are the products of one-electron reduction of aromatic quinones, the semiquinones. Both semidiones and semiquinones can be protonated to give neutral radicals which are relatively stable. 

The autoxidation of cyclic ketones with dirhenium decacarbonyl under basic catalytic conditions produces dicarboxylic acids (68-73%) bicyclic ketones are converted into keto carboxylic acids and, when one ring is aromatic, quinones are obtained, e.g. 1-tetralone produces 2-hydroxy-1,4-naphthaquinone (93%), and H02C(CH2)4C0(CH2)3C02H (85%) is obtained from 1-decalone via a cyclic triketone [5]. 

Synthesis of the aromatic quinone pigment, melanin, is initiated by oxidation of the Tyr ring by tyrosinase. 

It was also shown that this aromatic quinone ketal dissociates at room temperature as follows... 

The ready evolution of the adducts into aromatic quinones by spontaneous sulfinyl elimination and further aromatization prompted the use of sulfinyl naphthoquinones as a synthetic equivalent of the unknown compound naph-thynoquinone [103]. For this purpose, sulfinyl quinones represent a convenient synthetic alternative to haloquinones. The highly regioselective course of the Diels-Alder reactions of 2-phenylsulfinyl-1,4-naphthoquinones (as well as their corresponding thioethers and sulfones) unsymmetrically substituted by... 

Compounds with potentially sensitive groupings are dehydrogenated using Mn02, for example, the reduced quinolone (55) yields the fully aromatic quinone (56) <91TL1307>. Successive treatments with DBN and DDQ convert the lactone (57 R = Me) to the product (28 R1 = R2 = Me) <87JHC603>. 

It was recognised that the plates were neat TTP and the needles molecular adducts of composition 4 (TTP) - guest. Our own work has confirmed and extended these results we have found three polymorphic forms of TTP (Figs. 13 and 14), have confirmed that only guests with aromatic character participate in the formation of these adducts (see Table 6), and have shown that the needles are all isomorphous channel inclusion compounds. We have also found that tetralin forms an inclusion compound but that decalin and cyclohexane do not. Heteroaromatics are permissible guests (e.g. pyridine and a-picoline) but not aromatic quinones (e.g. p-benzoquinone and 2-methyl-p-benzoquinone). Pyrene is the largest molecule which forms an inclusion compound while perylene and fluoranthene form (what appear to be) ti—7i -charge transfer compounds with TTP. 

Dyes based on anthraquinone and related polycyclic aromatic quinones are of great importance. Many of the most lightfast acid, mordant, disperse, and vat dyes are of this kind. The chromophore is the carbonyl group. 

The reaction of 4-vinylindan (430) with quinones (see the review [63]) was carried out at a ratio of diene to dienophile of 1 2. This led to the dehydrogenation of the adducts originally formed by the excess of dienophile to give the corresponding aromatic quinones. Under these conditions, benzoquinone gave compound (429) in moderate yield [1068, 1069]. The reaction with toluquinone and methoxyquinone apparently leads, in analogy with the reactions of styrene with these quinones [1067], to compounds of the... 

Actinomycete (CNH-099) Sediment San Diego Isomarinone, Neomarinone and other aromatic quinones Cytotoxics Hardtetof, 2000... 

Ortho quinones (and also aromatic a-diketones, o-phenylenediamine to yield quinoxalines as follows. 

As well as the cr-complexes discussed above, aromatic molecules combine with such compounds as quinones, polynitro-aromatics and tetra-cyanoethylene to give more loosely bound structures called charge-transfer complexes. Closely related to these, but usually known as Tt-complexes, are the associations formed by aromatic compounds and halogens, hydrogen halides, silver ions and other electrophiles. 

Diketones and tetraketones derived from aromatic compounds by conversion of two or four SCH groups into keto groups, with any necessary rearrangement of double bonds to a quinonoid structure, are named by adding the suffix -quinone and any necessary affixes. 

Reaction with Organic Compounds. Aluminum is not attacked by saturated or unsaturated, aUphatic or aromatic hydrocarbons. Halogenated derivatives of hydrocarbons do not generally react with aluminum except in the presence of water, which leads to the forma tion of halogen acids. The chemical stabiUty of aluminum in the presence of alcohols is very good and stabiUty is excellent in the presence of aldehydes, ketones, and quinones. 

The close electrochemical relationship of the simple quinones, (2) and (3), with hydroquinone (1,4-benzenediol) (4) and catechol (1,2-benzenediol) (5), respectively, has proven useful in ways extending beyond their offering an attractive synthetic route. Photographic developers and dye syntheses often involve (4) or its derivatives (10). Biochemists have found much interest in the interaction of mercaptans and amino acids with various compounds related to (3). The reversible redox couple formed in many such examples and the frequendy observed quinonoid chemistry make it difficult to avoid a discussion of the aromatic reduction products of quinones (see Hydroquinone, resorcinol, and catechol). 

Hydrogen bromide adds to acetylene to form vinyl bromide or ethyHdene bromide, depending on stoichiometry. The acid cleaves acycHc and cycHc ethers. It adds to the cyclopropane group by ring-opening. Additions to quinones afford bromohydroquinones. Hydrobromic acid and aldehydes can be used to introduce bromoalkyl groups into various molecules. For example, reaction with formaldehyde and an alcohol produces a bromomethyl ether. Bromomethylation of aromatic nuclei can be carried out with formaldehyde and hydrobromic acid (6). 

Tetracyanobenzoquinone [4032-03-5] 3,6-dioxo-l,4-cyclohexadiene-l,2,4,5-tetracarbonitrile, is a remarkably strong oxidizing agent for a quinone it abstracts hydrogen from tetralin or ethanol even at room temperature (50). It is a stronger TT-acid than TCNE because it forms more deeply colored TT-complexes with aromatic hydrocarbons. 

DJERASSI RYLANDER Oxidation Ru04 in oxidative cleavage ot phenols or alkenes oxidation ol aromatics to quinones oxidation ol alkyl amides to irmdes or ol ethers lo esters... 

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

The mechanism of this reaction has been studied by several groups [133,174-177]. The consensus is that interaction of ester with the phenolic resole leads to a quinone methide at relatively low temperature. The quinone methide then reacts rapidly leading to cure. Scheme 11 shows the mechanism that we believe is operative. This mechanism is also supported by the work of Lemon, Murray, and Conner. It is challenged by Pizzi et al. Murray has made the most complete study available in the literature [133]. Ester accelerators include cyclic esters (such as y-butyrolactone and propylene carbonate), aliphatic esters (especially methyl formate and triacetin), aromatic esters (phthalates) and phenolic-resin esters [178]. Carbamates give analogous results but may raise toxicity concerns not usually seen with esters. 

Under the influence of peroxides aromatic amines (color developer 3) react with phenols to yield quinone imines [1]. 

Aromatic amine + 1-Naphthol-----------------> Quinone imine dyestuff. 

Ceric ammonium nitrate converts a 1,4-dimethoxy aromatic compound to the quinone, which is reduced with sodium dithionite to give a depro-tected hydroquinone. ... 

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