Quinones reactions with

The mercaptol alcohol rac-14 undergoes facile Michael addition reaction with quinone ketal 13 which is commercially available or can be readily prepared. 

There are two kinds of redox interactions, in which ubiquinones can manifest their antioxidant activity the reactions with quinone and hydroquinone forms. It is assumed that the ubiquinone-ubisemiquinone pair (Figure 29.10) is an electron carrier in mitochondrial respiratory chain. There are numerous studies [235] suggesting that superoxide is formed during the one-electron oxidation of ubisemiquinones (Reaction (25)). As this reaction is a reversible one, its direction depends on one-electron reduction potentials of semiquinone and dioxygen. 

Similar waves in the cathodic polarogram were observed by Donnet and Henrich 58) using oxidized carbon black. The wave disappeared after treatment with isobutyronitrile. It was assumed that isobutyro-nitrile gives an addition reaction with quinones. No reaction with this reagent was observed after reduction with hydrogen iodide, after treatment with aniline, or after treatment with diazomethane. The latter finding confirms the assumption by Studebaker et al. 38) that diazomethane is added to the quinones in the carbon black surface. 

Enamines, reaction with quinones, 20, 3 Enantioselective aldol reactions, 67, 1 allylation and crotylation, 73, 1 Ene reaction, in photosensitized oxygenation, 20, 2 Enolates ... 

HO2 and 02 have characteristic absorption spectra with s ax 140 mol at 225 nm [83] and Smav = 189 mol at 245 nm [85], respectively, which are sufficiently intense to permit their reactions to be followed by direct observation in pulse radiolysis experiments. Both radicals are relatively unreactive with organic molecules [83], abstracting only weakly bonded hydrogen atoms in, for example, ascorbic acid, cysteine, and hydroquinone. Oj undergoes reversible electron transfer in its reaction with quinones (Q), which was used to establish its reduction potential [86] ... 

The imine bond of 4H- and 6H- 1,3-oxazines enters into addition reactions with quinones and alcohols. Thus, for example, the triphenyl derivative (50) forms a 1 1 adduct with 1,4-benzoquinone (69LA(723)lll) and the oxazin-6-ones (51), when heated in methanol, give 2-methoxy-2,3-dihydro derivatives (Scheme 15) (72CJC584). 

The H2-D2 exchange occurs to an appreciable extent only under conditions when H (or D2) is not being absorbed rapidly in a chemical reaction such as the reduction of quinone or cupric acetate. This is consistent with the idea that the rate-determining step in the reduction is the activation of hydrogen by cuprous acetate (reaction (11)], the activated hydrogen being rapidly removed by reaction with quinone or Cu before it can return to the gas phase. 

The use of tertiary enaminones in the reaction with quinones to give benzofurans is a long known reaction140. If acetylbenzoquinone is used as the starting material, the resulting benzofuran141 (whose structure had to be corrected)142 (equation 93) can be transformed to furanobenzopyrans. 

Reactions with quinones, anthraquinone synthesis. Early studies of McElvain indicated that the reagent reacts in two different ways with quinones. In the case of benzoquinones the products are 1 1 adducts, which are ethoxyfurane derivatives. 2-Halonaphthoquinones were found to react at least in part with 2 equiv. of 1 to form 1,3-diethoxyanthraquinones (with loss of the halogen substituent). A more recent study established that the reaction of halonaphthazarins with 1 is stereospecific, i.e., only one anthraquinone is formed under suitable conditions yield of 1 2 adducts can be as high as 60 /o. A typical reaction is formulated in equation (I). The 1 1 adducts are major products, however, in the absence of a free peri-hydroxyl group. ... 

Reaction with quinones. Addition of an aqueous solution of sodium azide to a solution of a-naphlhoquinone in acetic acid is attended with rapid evolution of nitrogen and separation of orange-ied needles of 2-amino-1,4-naphlhoquinone in 87% yield. The reaction is interpreted as involving 1,4-addition of hydrazoic acid... 

Reaction with quinones [1, 447-448, at end]. Structure (5) assigned by Misiti, Moore, and Folkers8 to the product of the reaction of hydrazoic acid in sulfuric acid with trimethyl-p-benzoquinone has been shown to be incorrect by independent groups at the University of Manchester88 and the I.C.I. laboratories.811 The structure now regarded by both groups as correct is that shown in formula (6). 

Puri and co-workers [128,129] found that sulfur is introduced to the carbon matrix by interactions with oxygen-containing functional groups or by addition to unsaturated sites. Thus, the substitution reactions with quinone and phenolic groups lead to thioquinone and thiophenol structures, and the addition reactions result in the formation of sulfide and sulfoxide groups. Moreover, Chang showed the evidence of thiolactones in a number of carbonaceous materials after reaction with various sulfur-containing materials [126]. 

Addition of Germylenes to Multiple Bonds. Addition reactions of germylenes to the C=0 of para quinones typically yield alternating 2 1 polymers. An exception was noted for Ge[N(SiMe3)2)2 which gave a 1 1 polymer upon reaction with 1,4-quinones. Cyclic a, /3-unsaturated ketones and ethylene and propylene sulfide have also been found to be excellent monomers for the formation of alternating copolymers. Recall that related reactions with quinones and phenones noted in the Ge-C bond formation Section (3.1.7) lead to the dearomatization of the ring and the isolation of molecular products. For 1,4-napthoquinone, both molecular and polymeric products have been observed (equation 8). 

The nucleophilic reactivity of cysteine has been exploited in Michael reactions with quinones. One example is a water-soluble naphthoquinone, which has been entrapped in chlorophyll-containing vesicles in order to study light-induced electron transfer through a membrane from glutathione to the quinone (Fore, 1983). Another example is an asymmetrical vesicle membrane made of a cysteine quinone carboxylate bolaamphiphile, where all the quinone is localized on the outer surface of the vesicle (see Scheme 7.2.6 Scheme 9.5.1). 

In previous sections, several examples were shown using alkoxydienes or alkoxyalkenes. Acyloxy dienes are very useful in organic synthesis. One example is Bohlmann s synthesis of liglularone, which used acetoxy-diene 139 in a reaction with quinone 140 to give 141.1 An attractive feature of dienes that contain a vinyl... 

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