Quinone chemistry

Photochemical Reactions. Increased knowledge of the centraUty of quinone chemistry in photosynthesis has stimulated renewed interest in their photochemical behavior. Synthetically interesting work has centered on the 1,4-quinones and the two reaction types most frequentiy observed, ie [2 A 2] cycloaddition and hydrogen abstraction. Excellent reviews of these reactions, along with mechanistic discussion, are available (34,35). 

A more recent development in quinone chemistry has been the tandem reaction sequence. In seeking elegant syntheses of complex molecules, careful orchestration of transformations has become essential. The use of the Thiele-Winter reaction in tandem with arylation gives good yields of pharmacologically interesting heterocycles, such as (62), from 2,5-dihydroxy-l,4-ben2oquinone [615-94-1] and pyridines, where R = H or CH (60). 

Monks, T.J., Hanzlik, R.P., Cohen, G.M., Ross, D., and Graham, D.G., Contemporary issues in toxicology. Quinone chemistry and toxicity, Toxicol Appl Pharmacol, 112, 2, 1992. 

During his early years as an academician Fieser became one of the world s leading experts in quinone chemistry, his most notable... 

Isoprenylated Quinones.—Chemistry. An efficient method has been described for the preparation of ubiquinone-1 (221) and plastoquinone-1 (223) from the parent quinone and allyltributyltin. The synthesis of ubiquinone-10 by isoprenoid chain-elongation of a ubiquinone-1 derivative has been reported.The sul-phone derivative of the protected ubiquinol-1 (224) on reaction with solanesyl bromide (225) and McjCOK gave the sulphone (226) in 90% yield. Benseker reduction to remove the PhCH2- and PhS02-groups, followed by oxidation in air, afforded ubiquinone-10 (222). 

Umpolung.—In designing synthetic routes, it is occasionally desirable to reverse the normal reactivity at a particular centre. This principle of umpolung has been illustrated in quinone chemistry. Quinones are normally susceptible to nucleophilic attack e.g. Scheme 10). Manning et al. have shown how to reverse this reactivity, illustrated in Scheme 11, and are intending to apply the method to the syntheses of natural products. 

To extend the quinone chemistry, polyanilines and quinonediimines as 3t-conjugated polymers or molecules are studied to serve as organic catalysts for proton-conjugated electron transfer. Dimension of t-conjugated systems is controlled by use of a porphyrin or its zinc complex as a molecular scaffold to permit photorefractive electron transfer. 

Quinonoid compounds have been thoroughly reviewed (4,6). More recent trends in quinone addition and substitution chemistry were reviewed in 1993 (7). The quinone system in natural products has also been covered (8) there has been a fascinating discussion of the quinone problem (9). 

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). 

An example of the Michael chemistry, typical of all quinones bearing a replaceable hydrogen, is the preparation of a sulfone (6) (in 55% yield), which was ultimately converted to a polystyrene redox polymer (11). 

One of the most exciting discoveries related to quinone/hydroquinone chemistry is thek synthesis by biosynthetic routes (12,13). Using bacterial enzymes to convert D-glucose [50-99-7] (7) to either 1,2- or l,4-ben2enediol allows the use of renewable raw material to replace traditional petrochemicals. The promise of reduced dependence on caustic solutions and the use of transition-metal catalysts for thek synthesis are attractive in spite of the scientific and economic problems still to be solved. 

Quinones of various degrees of complexity have antibiotic, antimicrobial, and anticancer activities, eg, a2iddinornitosene [80954-63-8] (36), (-)-2-methyl-l,4-naphthoquinone 2,3-epoxide [61840-91 -3] (37), and doxombicin [23214-92-8] (adriamycin) (38) (see Antibiotics Chemotherapeutics, anticancer), ah of these natural and synthetic materials have stimulated extensive research in synthetic chemistry. 

Addition Reactions. The addition of nucleophiles to quinones is often an acid-catalyzed, Michael-type reductive process (7,43,44). The addition of benzenethiol to 1,4-benzoquinone (2) was studied by A. Michael for a better understanding of valence in organic chemistry (45). The presence of the reduced product thiophenyUiydroquinone (52), the cross-oxidation product 2-thiophenyl-1,4-benzoquinone [18232-03-6] (53), and multiple-addition products such as 2,5-(bis(thiophenyl)-l,4-benzoquinone [17058-53-6] (54) and 2,6-bis(thiophenyl)-l,4-benzoquinone [121194-11-4] (55), is typical ofmany such transformations. 

The most extensive mechanistic studies of quinone Michael addition chemistry involve the arylsufinic acids, which yield reduced product (50,51). The sulfones produced in such reactions have been examined electrochemicaHy (48) and kineticaHy (52). The influence of substitutents in the quinone has... 

Information on nucleophilic addition chemistry of quinones and various mechanistic rationali2ations have been discussed, and molecular orbital calculations have been proposed as more definitive approaches for explanation and prediction (63). 

The problems associated with predicting regioselectivity in quinone Diels-Alder chemistry have been studied, and a mechanistic model based on frontier molecular orbital theory proposed (85). In certain cases of poor regioselectivity, eg, 2-methoxy-5-methyl-l,4-ben2oquinone with alkyl-substituted dienes, the use of Lewis acid catalysts is effective (86). 

The kinetics of formation and hydrolysis of /-C H OCl have been investigated (262). The chemistry of alkyl hypochlorites, /-C H OCl in particular, has been extensively explored (247). /-Butyl hypochlorite reacts with a variety of olefins via a photoinduced radical chain process to give good yields of aUyflc chlorides (263). Steroid alcohols can be oxidized and chlorinated with /-C H OCl to give good yields of ketosteroids and chlorosteroids (264) (see Steroids). /-Butyl hypochlorite is a more satisfactory reagent than HOCl for /V-chlorination of amines (265). Sulfides are oxidized in excellent yields to sulfoxides without concomitant formation of sulfones (266). 2-Amino-1, 4-quinones are rapidly chlorinated at room temperature chlorination occurs specifically at the position adjacent to the amino group (267). Anhydropenicillin is converted almost quantitatively to its 6-methoxy derivative by /-C H OCl in methanol (268). Reaction of unsaturated hydroperoxides with /-C H OCl provides monocyclic and bicycHc chloroalkyl 1,2-dioxolanes. 

Coenzyme Q (Section 24.14) Naturally occurring group of related quinones involved in the chemistry of cellular respiration. Also known as ubiquinone. 

Cyclotrithiazyl chloride is also a useful reagent in organic chemistry in the fusion of 1,2,5-thiadiazoles to quinones as well as the synthesis of (a) isothiazoles from 2,5-disubstituted furans and (b) bis-1,2,5-thiadiazoles from A-alkylpyrroles (Scheme 8.4). Alkenes and alkynes react readily with (NSC1)3 to give 1,2,5-thiadiazoles, while 1,4-diphenyl-1,3-butadiene gives a variety of heterocyclic products including a bis(l, 2,5-thiadiazole). ... 

Photo-de-diazoniation has found relatively little application in organic synthesis, as is clearly evident from the annual Specialist Periodical Reports on Photochemistry published by the Royal Society of Chemistry. Since the beginning of these reports (1970) they have contained a section on the elimination of nitrogen from diazo compounds, written since 1973 by Reid (1990). In the 1980s (including 1990), at least 90% of each report is concerned with dediazoniations of diazoalkanes and non-quinon-oid diazo ketones, the rest being mainly related to quinone diazides and only occasionally to arenediazonium salts. 

Q-Flex QDI Quinone Diimine Antidegradant—Improved Mixing Chemistry Resulting in a Better Balance of Productivity and Performance... 

The results of the modeling smdy of the chain transfer chemistry have been published elsewhere. Quinone diimines are predicted to be more than two orders of magnimde more reactive toward free radicals than the corresponding PPD. The reactivity of a radical with another molecule should be related to the Lowest Unoccupied Molecular Orbital (LUMO) energy of that molecule. The reaction of a radical with a PPD differs from the reaction of a radical with QDI. 

FIGURE 8.25 Quinones produced from pyrene and benzo[a]pyrene. (From Neilson, A.H. and Allard, A.-S. The Handbook of Environmental Chemistry, Springer, 1998. With permission.)... 

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