Anthraquinone 1-methoxy

There is a wide diversity of chemical structures of anthraquinone colorants. Many anthraquinone dyes are found in nature, perhaps the best known being alizarin, 1,2-dihydroxyanthraquinone, the principal constituent of madder (see Chapter 1). These natural anthraquinone dyes are no longer of significant commercial importance. Many of the current commercial range of synthetic anthraquinone dyes are simply substituted derivatives of the anthraquinone system. For example, a number of the most important red and blue disperse dyes for application to polyester fibres are simple non-ionic anthraquinone molecules, containing substituents such as amino, hydroxy and methoxy, and a number of sul-fonated derivatives are commonly used as acid dyes for wool. 

Electron-donating groups (amino, methylamino, hydroxy, methoxy) in the 2-position, on the other hand, are extremely undesirable because, unlike similar substituents in the 1,4-positions, they are unable to form intramolecular hydrogen bonds with the keto groups of anthraquinone and hence are highly susceptible to photo-oxidation [167]. 

Photoamination of 7-methoxy-l,2-dihydronaphthalene in the presence of p-dicyanobenzene similarly affords the amine 153147 and l-benzamido-9,10-anthraquinone reacts with butylamine under UV irradiation in air to yield 154148. 

Sodium methylate acting on 2-chloroanthraquinone substitutes the methoxy group for chlorine and produces anion-radicals of the substrate (Shternshis et al. 1973). The study of kinetics has demonstrated that the amount of substrate anion-radical hrst increases and then sharply decreases. The inhibitor (p-BQ) decelerates the formation of anion-radicals. The rate of formation of 2-methoxy-anthraquinone also decreases. If anion-radicals are produced on the side pathway, the rate of formation of the end product on introduction of the inhibitor should not have decreased. Moreover, it should even rise because oxidation of anion-radicals regenerates uncharged molecules of the substrate. Hence, the anion-radical mechanism controls this reaction. 

A method for synthesis of anthraquinones is by reaction of cyanophthalide carban-ions with benzynes [162], It is particularly useful for the access of 2 aza-l,3,8-trimeth-oxyanthraquinone because of the high regioselectivity imposed by the methoxy groups and the nitrogen atom of the pyridine. 

When l,2,3,4-tetrafluoro-9,10-anthraquinone reacts with sodium methoxide, the methoxy group replaces the fluorine atom mainly in the 2-position to give 1,2,4-trifluoro-3-methoxy-9,10-anthraquinone (47). 14... 

XIX Anthragallol-2-methyI ether — 1,3-Dihydroxy-2-methoxy-anthraquinone... 

XX Anthragallol-3-methyl ether — 1,2-Dihydroxy-3-methoxy-anthraquinone... 

The X-ray structures of two anthraquinone derivates of 1,3-dioxane were published. In both 1 -methoxy-4-(2-methylprop-2-enyloxy)-2-[(2i ,6i )-4,4,6-trimethyl-1,3-dioxan-2-yl]-anthraquinone and 4-hydroxy-3-(2-methyl prop-2-enyloxy)-2-[(27 ,67 )-4,4,6-trimethyl-l,3-dioxan-2-yl]anthraquinone the 1,3-dioxane ring adopts the chair conformation and the substituents in positions 2 and 6 are in equatorial conformations (99AX(C)436). Finally, Freeman et al. (02JMS(T)43), employing both ab initio theory and density function theory, calculated the energies of chair, half-chair, sofa, twist, and boat conformers of 1,3-dioxane. 

Amino- and methoxy-substituted derivatives of l-acyloxy-9,10-anthraquinone... 

Scheme 13) and 9-acetoxy-l,4-anthraquinone (IIA, R1 = OCOCH3, R2= R3 = H) (Scheme 14) in a glassy matrix at 77 k. 19,21,34 It was found that photochromic transformations occurred only in acetoxyanthraquinones with electron-donating substituents (amino and methoxy groups) and also in unsubstituted 9-acetoxy-l,4-anthraquinone. However, unsubstituted I-acetoxy-9,10-anthraquinone and its derivatives with the substituents in 2-,4-,5- and 8-positions did not exhibit photochro-mism (Table 7.2).21,28,34... 

Figure 7.4. Absorption spectra of l-acetoxy-2-methoxy-9,10-anthraquinone (1, 2)28and 9-acetoxy- 1,4-anthraquinone in ethanol at 77 K (3, 4)34 before (1, 3) and after (2, 4) UV irradiation.

The lifetime of the photoinduced form for a number of these compounds lay in the microsecond range except for those of l-arylcyanomethyl-9,10-anthraquinones36 and l-methyl-4-oxy-9,10-anthraquinone.17 The lifetime of the photoinduced form for these compounds amounted to several minutes. The enhanced stability of the photoinduced form of l-phenylcyanomethyl-4-methoxy-9,10-anthraquinone was responsible for a number of irreversible photochemical transformations of this compound. 

The substituents in the anthraquinone ring affected the rate constant of thermal bleaching of derivatives of 1-methylphenoxyanthraquinone (Table 7.1).17,18,26 The substituents that increased the Tt-electron density on the hydrogen atom of the methide group decreased the lifetime of the photoinduced form (Table 7.1).18,26 The introduction of methoxy and piperidine substituents stabilized the photoinduced form (Table 7.1). 

Irreversible photochemical transformations were observed for photochromic phenyl-containing l-carbamoyloxy-2-methoxy-9,10-anthraquinones.25 The formation of photoproducts depended strongly on the water concentration in organic solutions. 

N. P. Gritsan, A. Kellmann, F. Tfibel, and L. S. Klimenko, Laser flash photolysis study of the primary processes in the photochromic reaction of l-acyloxy-2-methoxy-anthraquinones, Mol. Cyst. Liq. Cryst. 246, 259-262 (1994). 

Methoxy-pseudobaptigenin-7-0-(3-glucoside (isoflavone O-glycoside) Morindone (anthraquinone)... 

Treatment of 1,2-. 1,4-, 1,5-, and 1,8-dimethoxyanthra-quinone with BF, etherate in Cf,H (reflux) result.s in difluoroboron chelates, which are hydrolyzed to the corresponding l-hydroxy-2-methoxy-, -4-methoxy-, -5-methoxy-, and -8-methoxyanthraquinones when heated in CH,OH. This selective dealkylation can be used to convert 1,4,5-trimethoxyanthraquinone (1) into either 4-hydroxy-1,5-dimethoxy-anthraquinone (4) or l,4-dihydroxy-5-methoxyanthraquinone (5). 

Regiosehctive anthraquinone synthesis. The methoxy-substituted phthalic anhydride 1 reacts with the Grignard reagent 2 to give essentially only the pseudoacid 3. The product is cyclized (cone. H2SO4, 25°) and demethylated (HBr-HOAc) to digitopurpone (4) in 51% overall yield. 

We wondered if this reaction might be exploited to construct the angularly condensed benzo[a]anthracenes. A problem was the aromatization of the initially formed hydroaromatic ring A under the relatively drastic basic reaction conditions. The starting material 12 was synthesized in a stepwise manner from l-hydroxy-5-methoxy-9,10-anthraquinone [23]. The crucial cyclization can mechanistically be regarded as an intramolecular nucleophilic displacement of the methoxy group to afford a keto ester 13 with about 55% yield (Scheme 5). Only a few nucleophilic additions to electron-deficient anthraquinones are known [20,24,25] and intramolecular reactions of this type are more facile [21, 26-30]. The subsequent ethoxydecarbonylation under acidic conditions to yield ketone 14 presented no problem. 

In 1,2-disubstituted series such as cis- and frans-2-alkyl-l-alkoxybenzocyclobutenok, the traits isomer is more likely to lead to a high yield of cycloaddition product than the cis since the 1,5-hydrogen shift is precluded, llie forced inward rotation of an aryl substituent in 1-methoxy-l-phenylbenzocyclobutene is potentially advantageous and leads to anthracene derivatives." See also the anthraquinone synthesis fiom the corresponding benzocyclobutenones (Section 6.1.5). 

Methylaminoanthraquinone has been prepared from 1-chloro-, 1-bromo-, and 1-nitroanthraquinone by treatment with alcoholic methylamine under pressure from 1-methoxy- and 1-phenoxyanthraquinone with methylamine in pyridine solution at 150° from potassium anthraquinone-1-sulfonate with aqueous methylamine at 150-160° from 1-aminoanthraquinone by treatment with formaldehyde, or methyl alcohol in sulfuric acid or oleum and by hydrolysis of />-toluenesulfonyl-methylaminoanthraquinone with sulfuric acid. ... 

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