Simple 1,4-Naphthoquinones

The more intensely colored 1,4-naphthoquinones with amino and/or hydroxyl groups in the 5- and 8-positions are analogous to the commercial anthraquinone dyes, but are generally more bathochromic [10], For example, 5-methylamino-1,4-naphthoquinone has Xmax 529 nm in cyclohexane, whereas 1-methylaminoanthraquinone has Xmax 495 nm. This is also true for the 5,8-disubstituted naphthoquinones, but this potential advantage has not proved of commercial significance, and few such compounds have been considered as textile dyes. An exception is 5-amino-2,3-dichloro-8-hydroxy-l,4-naphthoquinone (4) [68217-33-4], which has been claimed as a violet disperse dye for acetate fibers [14], Naphthazarin (1) is an example of a 5,8-disubstituted naphthoquinone of greater value as an intermediate than as a dyes. 

When auxochromes such as NHR or OH are present in both rings of the naphthoquinone system, the absorption spectrum consists of two overlapping bands, and this can result in dull colors, typically blue-grays. A 3-cyano group appears to counteract the dulling effect, and 5 [79469-30-0] has been described as a blue dye for polyester [15], 

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As with the simple 1,4-naphthoquinones, most recent research activity in the heteroannelated compounds has been directed towards the development of dyes that absorb in the near-infrared. Noteworthy is the dithiadinaphtho-1,4-naphthoquinone system 16 (X = S), which can be prepared by condensing 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone with 2-aminothiophenol [25], The parent compound 16 (X = S) [96692-25-0] shows multiple absorption bands between 400 and 800 nm, with the most intense peak at 725 nm in chloroform (rmax 15 200 L mob1 cm-1) [25], Oxidation of the sulfur atoms to SO groups produces a large bathochromic shift, and 16 (X = SO) shows a peak at 827 nm (emax 17 600 L mol-1 cm-1) in chloroform [25],... 

Recently, a minor yellow-orange pigment from Trichia floriformis has been identified as 2,3,5-trihydroxy-l,4-naphthoquinone (281) by comparison with synthetic material (156). This simple naphthoquinone is most likely derived by oxidative degradation from a trichione type precursor. Further pigments are produced by T. floriformis as a result of intermolecular condensation between molecules of the trichione type. The structures of these more complex naphthoquinone pigments remain to be completely elucidated (156, 438). 

A representative of simple naphthoquinones is yellow-orange lawsone (2-hydroxynaphtho-l,4-quinone, 9-150), which occurs as a mixture of several naphthoquinones in henna Lawsonia inermis, Lythraceae) growing in the Middle East and India, but also located in many other plants. The pigment, which exhibits antimicrobial effects, is obtained from the leaves of henna bushes, used for centuries for decorating hands, feet, nails and skin, as well as hair dye. 

When just a trace of dark impurity is present, as in some of the commercial preparations, a completely pure product is easily obtained by vacuum distillation, but the ordinary crude reaction product is likely to decompose when treated in this manner. The ether method introduced in the present procedure has the advantage of being simple and efficient. It is equally applicable to the purification of the homologues of a-naphthoquinone. 

Al-Ghannam et al. [25] described a simple fluorimetric procedure for determination of three pharmaceutical compounds containing thiol groups, including penicillamine. In this method, the drugs are treated with 1,2-naphthoquinone-4-sulfonic acid. The later compound is reduced to l,2-dihydroxynaphthalene-4-sulfonic acid, which is measured fluorimetrically (excitation = 318 nm, emission = 480 nm). The method is sensitive to 0.5 1.5 pg/mL, with a detection limit of 0.05 pg/mL (S/N = 2). 

The pioneer work on this subject using simple 1-azadienes is due to Ghosez et al. (82TL3261 85JHC69) they succeeded in reacting 1-azadienes as 47r-electron components in Diels-Alder cycloadditions. Thus, l-dimethylamino-3-methyl-l-azabuta-l,3-diene (a,/3-unsaturated hydrazone) 54 did undergo [4 + 2] cycloaddition to typical electron-poor dienophiles, e.g., methyl acrylate, dimethyl fumarate, acrylonitrile, maleic anhydride, and naphthoquinone, producing pyridine derivatives 55-57 (Scheme 14). 

Bcnzofuran-4,7-dioncs have been synthesized regioselectively by [3 + 2] photoaddition of 2-hydroxy-1,4-benzoquinones with a range of alkenes (equation 185)664. The reaction occurs in 30-60% yield and is a useful method for the synthesis of the benzofuran ring system, which is important in natural products like acamelin665. Substituted naphthoquinones may also be used in this reaction666,667 and this has lead to a very simple two-step synthesis of maturinone. In a similar reaction, a [3 + 2] photoaddition reaction of 2-amino-1,4-naphthoquinones with electron-rich alkenes gave 13-82% yields of 2,3-dihydro-177-bcn/ /]indole-4,9-diones in a single-step process which involved photolysis followed by oxidation (equation 186)668,669. 

A number of "binaphthyldiquinones" have recently been found as natural products, and Russian workers have described a very simple, one-step method for preparation of the basic system. Thus, diquinone la was obtained in 40% yield simply by heating a solution of 1,4-naphthoquinone with two equivalents of sodium hydride in THF. Use of 2-chloro- or 2-bromo-1,4-naphthoquinone gave the diquinones lb and lc in 94 and 92% yield respectively. 

Several synthetic compounds containing the naphthoquinone skeleton, such as 2-(4-cyclohexylcyclohexyl)-3-hydroxy- 1,4-naphthoquinone [169], are effective in the treatment of coccidial infection. Two structurally related antibiotics WS-5995A (36) and WS-5995B (37a), isolated from S. auranticolor sp. nov. near Tokyo, efficiently protect Eimeria tenella (a species of coccidia) infection. An inactive component WS-5995C (37b) can be readily converted to the active (36) by simple dehydration [ 170-172]. Compound (36), the structure of which resembles the aforementioned benz[a]anthraquinone antibiotics, is the first example of a 5//-benzo[d ]naphtho[ 2,3-6 ]pyran ring system found in nature. 

From about 1930 onwards, developments in the field of naphthoquinone dyes concentrated on the use of naphthazarin and intermediates for the preparation of violet, blue, and green acid and disperse dyes [1]. More recently there has been interest in the synthesis and color and constitution properties of simple colored naphthoquinones, stimulated by the fact that such dyes have similar tinctorial properties to the anthraquinones but a smaller molecular size. The naphthoquinones provide a useful alternative to the anthraquinones for certain specialized applications, e g., as pleochroic dyes with improved solubility for liquid-crystal displays. As a result, research interest in these chromogens remains unabated, even though they have failed to make any major impact as textile dyes [2-8],... 

More than 50% of disperse dyes are simple azo compounds, about 25% are anthraquinones, and the rest are methine, nitro, and naphthoquinone dyes (see Sections 2.2, 2.3, 2.6, 3.12). 

The surface chemical effects of interest do not go as far as those induced in (extensively) modified carbon electrodes [248], e.g., by pyrolyzed phthalocyanines or macrocycles [249-255], by anthraquinone or its derivatives [126,247,256-259], or by aryl groups [125], or those of stable and efficient sonoelectrocatalysts by modifying GC electrodes with 9,10-phenanthraquinone or 1,2-naphthoquinone [260], Instead, it is explored here whether and how a seemingly simple but crucial issue has been addressed or resolved what makes 02 adsorption in ORR nondissociative The isotopic labeling evidence for this experimental fact has been presented half a century ago [261], and it has not been challenged [262], The implication, based on the equally noncontrover-sial literature that 02 chemisorption on carbons (even at room temperature) is dissociative, is summarized below ... 

At the outset of this chapter, we noted that the beauty of symmetry and pattern is ultimately the beauty of simplicity. The elegance of the chemistry of these supra-molecular capsules, too, lies in the profound chemical consequences of simple changes wrought by the defined microenvironments within these assemblies. The earliest examples of altered chemical activity within supramolecular coordination compounds come from Fujita and coworkers, in which they employed their palla-dium-vertexed octahedra (Fig. 16) in the Diels-Alder cycloaddition of isoprene with naphthoquinone [26], accelerating this bimolecular addition 113-fold. 

A key step in the synthesis of the simple aromatic bisphenol tetrangulol (3) by Brown and Thomson [18] was a Michael-type cyclization of a phenol to the chloronaphthoquinone moiety (Scheme 3). The starting material 8, connecting the naphthoquinone and the protected phenol, was prepared by an interesting radical alkylation of the chloronaphthoquinone 6 with a carboxylic acid 7 in the presence of silver ions and persulfate with concomitant decarboxylation (Torsell reaction [19]) to yield the dihydrobenzo[a]anthraquinone 9. The synthesis of tetrangulol (3) was concluded by dehydrogenation in boiling nitrobenzene. 

The cycloaddition of simple dienophiles, such as methacrolein (1) or methyl acrylate (2) catalyzed by various titanium complexes of chiral diols, for example 4-6 give mostly poor results811,12 with one exception. The addition of methacrolein (1) or 1,4-naphthoquinone (11a) to the 1,3-dienol derivative 3b, catalyzed by the titanium complex (R)-4, gives an unexpectedly high diastereomeric ratio. 

This suggestion, coupled with the mouse skin-painting bioassay results reported by Takizawa (3865a) that several simple quinones such as 2,5-cyclohexadiene-l,4-dione (p-benzoquinone), 1,2-naphthalenedione (1,2-naphthoquinone), and 1,4-naphthalenedione (1,4-naphthoquinone) were tumorigenic to mouse skin, raised serious questions about the desirability of adding phenols to the tobacco blend to enhance the odor and flavor of its smoke. Despite the many studies in which benzene was used as the solvent for testing of the tumorigenicity of PAHs, benzene seldom induced tumors in... 

The most basic structural model for anthracyclines adriamycin (doxorubicin) and daunomycin (daunorubicin) was considered to be tiie strongly intramolecularly hydrogen-bonded naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) (Section 3.2). It is usually customary to study the way in which such simple quinones form radicals in order to gain insight into the way more complex quinones might produce toxic and other effects. This is more so as the radical centres in the complex molecules are usually located in these simpler model structures. Treatment of naphthazarin will also demonstrate how various data may be compiled and compared. 

Dioxobenzocyclobutene has also attracted interest for organic synthesis. In particular, much attention has been paid to the addition of carbon nucleophiles to the carbonyl group for transformation to naphthoquinone or indanone derivatives. Double additions of excess vinyllithium to (1,2-dioxobenzocyclo-butene)chromium complex 52 at -78 °C gave the tricarbonylchromium complex of 5,10-dioxobenzocyclooctene 53 in 87% yield without formation of simple diadduct (Eq. 38) [37]. Obviously, the product 53 was formed by a double addition of vinyllithium and subsequent anionic oxy-Cope rearrangement. 

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