Quinone methode

In comparison with manganese dioxide, the DDQ reagent has several advantages for the oxidation of allylic alcohols. The quinone method is more reproducible only one equivalent of oxidant need be added and generally fewer side reactions are observed. On the other hand, the workup of DDQ reactions often requires chromatography and in the simpler cases lower isolated yields may be realized. 

Entry n m-quinones Method Time (min) Amine (equiv.) Yield (%y>- ... 

Photosystem Il-enriched particles from A. nidulans to be used for EPR were obtained by extraction of membranes with sulfobetaine detergents as described in (4) and suspended in 16 mM Mes, pH 6.0 containing 20Z (v/v) glycerol, 0.4 M mannitol, 10 mM CaClz, 8 mM MgCla and 1.6 mM KbHPOa. Photosystem II membranes from spinach were prepared as in (5) and suspended in 20 mM Mes, pH 6.3, 15 mM NaCl, 5 mM MgClz and 400 mM sucrose. Oxidation of the PS II acceptor side was accomplished with 5 mM ferricyanide (1) or by the quinone method (2) with 2 mM phenyl-p-benzoquinone (PPBQ). Bicarbonate depletion was done by incubation with Na-formate in the dark for 30 minutes (6). EPR spectra were recorded with the equipment described in (7). 

The name proanthocyanidins, previously called leucoanthocyanidins, implies that these are colorless precursors of anthocyanidins. On heating in acidic solution, the C—C bond made during formation is cleaved and terminal flavan units are released from the oligomers as carbocations, which are then oxidized to colored anthocyanidins (cf. 18.1.2.5.3) by atmospheric oxygen (Formula 18.21). Base-catalyzed cleavage via the quinone methode is also possible. 

The importance of quinones with unsaturated side chains in respiratory, photosynthetic, blood-clotting, and oxidative phosphorylation processes has stimulated much research in synthetic methods. The important alkyl- or polyisoprenyltin reagents, eg, (71) or (72), illustrate significant conversions of 2,3-dimethoxy-5-methyl-l,4-ben2oquinone [605-94-7] (73) to 75% (74) [727-81-1] and 94% (75) [4370-61-0] (71—73). 

Various alkylating agents are used for the preparation of pyridazinyl alkyl sulfides. Methyl and ethyl iodides, dimethyl and diethyl sulfate, a-halo acids and esters, /3-halo acids and their derivatives, a-halo ketones, benzyl halides and substituted benzyl halides and other alkyl and heteroarylmethyl halides are most commonly used for this purpose. Another method is the addition of pyridazinethiones and pyridazinethiols to unsaturated compounds, such as 2,3(4//)-dihydropyran or 2,3(4//)-dihydrothiopyran, and to compounds with activated double bonds, such as acrylonitrile, acrylates and quinones. 

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. 

The procedure described is essentially that of Belleau and Weinberg and represents the only known way of obtaining the title compound. One other quinone acetal, 1,4,9,12-t6traoxadispiro[4.2.4.2]tetradeea-6,13-diene, has been synthesized by a conventional method (reaction of 1,4-cyclohexanedione with ethylene glycol followed by bromination and dehydrobromination ) as well as by an electrochemical method (anodic oxidation of 2,2-(l,4-phenylenedioxy)diethanol ). Quinone acetals have been used as intermediates in the synthesis of 4,4-dimethoxy-2,5-cyclohexadienone,. syw-bishomoquinone, - and compounds related to natural products. ... 

The only satisfactory method of preparing /3-naphthoquinone is by the oxidation of 1,2-aminonaphthol in acid solution, and the chief problem involved is that of the preparation of this intermediate in suitable yield and purity. This problem and the literature pertaining to it are discussed elsewhere. Most reports of the preparation of the aminonaphthol include some description of its oxidation, but the only particularly helpful comment on the reaction is that ferric chloride is a better oxidizing agent than chromic acid because at a low temperature it docs not attack the quinone, even when present in excess. ... 

One other method is from 1,2-bromonaphthol through the keto-nitrobromide. Though the parent quinone itself is such a sensitive compound that the material so obtained decomposed within a few hours, the method is of considerable value for the preparation of certain substituted -naphthoquinones. ... 

Benzofuroxan may be obtained by oxidation of o-quinone dioxime. The first benzofuroxan derivative, 1,2-naphthofuroxan, was obtained by this method. Suitable oxidizing agents include alkaline ferri-cyanide, bromine water, chlorine, and nitric acid. The method is of practical value only when the o-quinone or its monooxime (o-nitrosophenol) is readily available, and since this is not generally the case, other routes, e.g., the oxidation of o-nitroanilines and the thermal decomposition of o-nitrophenyl azides/ are more commonly used. 

Reduction of benzofuroxans is usually the most convenient route to benzofurazans and o-quinone dioximes (see Section VI, C). Reduction of 4-nitrobenzofuroxan would seem to be a method of synthesis of 1,2,3-triaminobenzene, while the haloalkoxy-substitution reaction (Section VTT,B) and the rearrangements of Section VIII provide compounds accessible only with difficulty by other methods. Apart from these reactions, the benzofuroxans appear to be of limited synthetic utility. 

B. Naphthaquinone method Discussion. Many primary amines develop a blue colour when treated with ortho-quinones the preferred reagent is the sodium salt of l,2-naphthaquinone-4-sulphonic acid. 

The only practical method for the preparation of anthra-quinone-a-sulfonates is that based upon the discovery 1 that in the presence of a small amount of mercuric salt anthraquinone is sulfonated chiefly in the a- rather than in the /3-position. Detailed procedures are described by Fierz-David,2 by Lauer,3 and by Groggins 4 the above directions are based largely upon the observations of Lauer.3... 

The procedure described above has been used to prepare various alkylated 1,4-benzoquinones and 1,4-napthoquinones,2-3 including some naturally occurring quinones.4 A few examples are listed in Table I to show the scope of the method. 

In the 1980 s three monographs were published that cover parts of the present book, namely Quinone Diazides, by Ershov, Nikiforov, and de Jonge (1981), Aromatic Diazo Compounds, by Saunders and Allen (1985), and Williams Nitrosa-tion (1988). The book of Saunders and Allen which is actually the third edition of Saunders original book (1936, 1949), focuses on synthesis and preparative methods. The other two books emphasize rather the mechanistic and physical organic aspects of their subjects. 

The other major route to quinone diazides is based on the alkaline hydrolyses of mono-4-toluenesulfohydrazones of quinones, which will be discussed in Section 2.6. In the same section other synthetic methods are briefly discussed. 

The Gomberg-Bachmann reaction is a method for arylation of aromatic compounds and quinones (Gomberg and Bachmann, 1924). Originally this reaction involved adding aqueous sodium hydroxide slowly to an intimate mixture of an aqueous solu-... 

Diels-Alder Reaction Facilitated by Physical and Chemical Methods 155 Table 4.8 o-Quinone ultrasound-assisted Diels-Alder reactions... 

Alkali metal reduction is a widely employed method for the preparation of radicals derived from various classes of conjugated compounds such as hydrocarbons, heterocycles, nitro compounds, quinones, and nitriles. For... 

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