Synthesis anthraquinones

Anthraquinone synthesis.1 The original anthraquinone synthesis (10, 75) from benzamides and benzaldehydes involving a tandem orf/io-lithiation can be improved by use of an ort/to-bromobenzaldehyde as the second component. In this version, the second lithiation involves halogen-metal exchange, which results in higher yields. In the example cited here, the yield was only 15% in the absence of the bromine substituent on the aldehyde. 

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. ... 

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. 

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). 

The direct synthesis of anthraquinone from phthalic anhydride and benzene has been reported to proceed over zeolite Beta [50] in a shape selective manner. In a conventional anthraquinone synthesis, anthracene is used as a feedstock for oxidation. Once there is a shortage of it in the market, additional anthracene could be produced by isomerization of its isomer, viz. phenanthrene. This, however, is not possible by direct isomerization of the trinuclear aromatic system but involves the partially (symmetrically) hydrogenated species. Consequently, isomerization of symmetrical octahydrophenanthrene to symmetrical octahydro-anthracene was studied by Song and Moffatt [51]. As sketched in Figure 3, a high yield of symmetrical octahydroanthracene can be obtained over zeolite H-mordenite (ngj/nyy = 8) at 250 °C (liquid phase, decalin as solvent). These examples show that (shape selective) catalysis on zeolites is more and more expanding into the conversion of polycyclic aromatics, and we foresee continued interest and success in this field of zeolite catalysis. 

Effenberger, R, Buckel, R, Maier, A. H., and Schmider, J. 2000. Perfluoro-alkanesulfonic acid catalyzed acylations of alkylbenzenes synthesis of alkyl-anthraquinones. Synthesis 1427-1430. 

Thus, anthraquinone synthesis in cell suspension cultures of Morinda oitrifolia depends strictly on auxins. However, among 14-6 substances showing auxin activity tested by Zenk et al. (37), only a few were able to trigger anthraquinone metabolism. Naphthalene-1-acetic acid was the most effective one. In contrast, the same cells cultivated in a medium containing 2,4-i) as the only auxin did not produce anthraquinone. 

Vasconsuelo, A., Giulietti, A. M., Boland, R. 2004. Signal transduction events mediating chitosan stimulation of anthraquinone synthesis in Rubia tinctorum. Plant Science 166 405 13. 

This suspension culture of Morinda cells is being studied because the biosynthesis of anthraquinones and its glycosides can be triggered in the culture. Upon transfer of cells into darkness and a medium containing sucrose the chlorophyll decreases and the lipoquinones (including phylloquinone) disappear from the cells (Table 1). Simultaneously, anthraquinone pigments are formed (Fig. 4) and the cultured cells turn yellow and eventually red. Thus, in the suspension culture photoautotrophy correlates with lipoquinone synthesis while heterotrophy correlates with anthraquinone synthesis. This reflects the situation in the intact plants where lipoquinones are associated with chloroplast whereas anthraquinones occur in the roots. 

Jeevitha D, Amarnath K. Chitosan/PLA nanoparticles as a novel carrier for the delivery of anthraquinone Synthesis, characterization and in vitro cytotoxicity evaluation. Colloids Surf B Biointerfaces. 2013 101 126-34. 

SCHEME 16.33 Double Diels-Alder/elimination reaction toward highly substituted anthraquinone synthesis. 

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