Xanthone reduction

Commercial xanthhydrol may be used, but the pure white product, m.p. 120-121°, obtained by the reduction of xanthone with sodium amalgam (Section VII,16) gives better results. 

The best results are obtained with freshly prepared xanthhydrol (reduction of xanthone with sodium amalgam. Section VII,16). Dissolve 0 -25 g. of xanthhydrol and 0 -25g. of the primary sulphonamide in 10 ml. of glacial acetic acid. Shake for 2-3 minutes at the laboratory temperature and allow to stand for 60-90 minutes. Filter oflf the derivative, recrystallise it from dioxan-water (3 1), and dry at room temperature under water pump suction for 30 minutes. 

The biological activity of flavonoids has attracted much interest in the part twenty years and a few compounds of this class have been shown to have AChEI effects. The flavanone naringenin (74) from Citrus junos (Rutaceae) ameliorated scopolamine-induced amnesia in mice, which may be related to an antiAChE effect, since naringenin was shown to inhibit AChE in vitro dose dependently. A recent theoretical study has shown that flavonoids and xanthones exhibit polyvalent effects such as antioxidant, amyloid reduction and cholinesterase inhibition, which made them interesting candidates for further studies. 

Metal hydrides usually reduce the carbonyl to alcohol but LAH converts xanthone into a dixanthyl ether (454) or xanthene (453) according to the conditions. The latter product is also obtained by the Wolff-Kishner-Huang-Minlon reduction. Metal-liquid ammonia opens the pyran-4-one ring of chromones and flavones to form dihydrochalcones and other compounds (79JOC1494). 

The reduction of xanthone to xanthene has been achieved by using the Huang-Minlon modification of the Wolff-Kishner reduction (52JCS3741) by LAH (55JA5121) and by diphenyl-silane (61JOC4817). 

The key intermediate in the total synthesis of furaquinocin was obtained in good yield by a reductive Heck reaction that proceeded with a sterically hindered base pentamethylpiperidine (PMP) <02JA11616>. A new hypothesis for the major skeletal rearrangement (anthraquinone —> xanthone —> coumarin) that occurs in the complex biosynthesis of aflatoxin Bi was proposed. To test this hypothesis, an intermediate 11-hydroxy-O-methylstergmatocystin (HOMST) was synthesized as shown below. The key transformation in this synthesis involved the treatment of an ester-aldehyde with Pr3SiOTf, which smoothly produced a mixed acetal. Direct reduction with DIBAL-H led to the aldehyde. The desired product was eventually obtained via several steps as shown <02JA5294>. 

Reduction of xanthones 851 in acid solution gives bimolecular reduction products (852, 853). 

Dihydroxyxanthones.1 KF in DMF is a more efficient catalyst than K2C03 for condensation of methyl salicylates with chlorobenzoquinones to provide phenoxybenzo-quinones (1). The products on reduction (Na2S204) and cyclization (H2S04) afford 1,4-dihydroxy xanthones (2) with high regioselectivity (equation I). 

A potentially useful chemoselective dissolving metal reagent for the reduction of aromatic ketones in the presence of other functional groups is the combination Zn-DMSO and aqueous potassium hydroxide. In three examples (benzophenone, fluorenone and 4-benzoylpyridine), the yields of secondary alcohols were over 90%. Two other ketones (xanthone and thioxanthone) gave mixtures of alcohol and the hydrocarbon obtained by hydrogenolysis of a carbon-oxygen bond. ... 

Reduction of ketones. Xanthone is reduced to xanthhydrol by shaking a suspension of the ketone in 95% ethanol at 60-70° with the liquid amalgam from 9 g. of sodium and 55 ml. of mercury. ... 

Derivation Reduction of xanthone with alcohol and sodium. 

Recently, a study on the synthesis of novel natural secondary allylic alcohol derivatives was carried out by Helesbeux et al. [64]. The photooxygenation-reduction sequence was apphed in the prenylated xanthone series also... 

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