7- Oxygenated xanthones

A review of the PMR spectra of phytoxanthones contains an extensive list of spectral data for oxygenated xanthones (79H(l2)42l). 

Co-occurrence of simply oxygenated xanthones and more complex prenylated structures has been described in the genus and the 1,3,5,6-oxygenation pattern appears to be the most common for the alkylated xanthones [72],... 

New oxygenated xanthones were characterized from heartwood, root and leaf extracts of H. geminiflorum [74,75], namely a) 2, 3-dihydroxy-... 

Sahin H, Nieger M, Nising CF, Erase S (2009) Functionalization of Highly Oxygenated Xanthones Unexpected Stereochemistry and Rearrangements. Synlett 3187... 

Isolation of Oxidation Products. After oxygen absorption had ceased, or reached the desired value, the oxidates were poured into water. In many cases the reaction product could be removed by filtration in high yield. In this manner xanthone (m.p. 172-174°C.), was isolated from oxidations of xanthene or xanthen-9-ol thioxanthone (m.p. 208-210°C.), from thioxanthene acridine (m.p. 107-109°C.), from acridan anthracene (m.p. 216-217°C.), from 9,10-dihydroanthracene phenanthrene (m.p. 95-99°C.), from 9,10-dihydrophenanthrene pyrene (m.p. 151-152.5°C.) (recrystallized from benzene) from 1,2-dihydropyrene and 4-phenan-throic acid (m.p. 169-171 °C.) (recrystallized from ethanol) by chloroform extraction of the hydrolyzed and acidified oxidate of 4,5-methyl-enephenanthrene. 

XVII XVII, 1st Supplement (combined with Volumes XVIII and XIX) XVII, 2nd Supplement 1933 1934 1952 2359-2503 2359-3031 2359-2503 One Cyclic Oxygen (S, Se or Te). Stem nuclei Furan, 27. Thiophene, 29. Hydroxy compounds Furfuryl alcohol, 112. Carbonyl compounds Butyrolactone, 234. Furfural, 272. 2-Aeetyl-thio-phene, 287. Xanthone, 355. Succinic anhydride, 404. Phthalic anhydride, 469. 

Alneri et al.2 have catalyzed autoxidation of xanthone (175) and thio-xanthone (176) by molecular oxygen, using PTC. 

Based on steady-state and time-resolved emission studies, Scaiano and coworkers have concluded that silicalite (a pentasil zeolite) provides at least two types of sites for guest molecules [234-236], The triplet states of several arylalkyl ketones and diaryl ketones (benzophenone, xanthone, and benzil) have been used as probes. Phosphorescence from each molecule included in silicalite was observed. With the help of time-resolved diffuse reflectance spectroscopy, it has been possible to show that these triplet decays follow complex kinetics and extend over long periods of time. Experiments with benzophenone and arylalkyl ketones demonstrate that some sites are more easily accessed by the small quencher molecule oxygen. Also, diffuse reflectance studies in Na + -X showed that diphenylmethyl radicals in various sites decay over time periods differing by seven orders of magnitude (t varies between 20/is and 30 min) [237]. 

The t3C resonances of xanthone (21) have been assigned on the basis of shift analysis of the structurally related compounds anthrone and xanthene (77P735) and by correlation with the component molecules diphenyl ether and benzophenone (78T1837). Delocalization of the non-bonding electron pairs at oxygen, leading to an increase in aromaticity of the pyranone ring, accounts for the deviation of the chemical shifts of C-4a, C-8a and the carbonyl carbon atom from the calculated values. 

Much of the synthetic chemistry of xanthones has arisen out of their natural occurrence, a topic which has been reviewed (61CRV591), and also as a result of their incorporation into dyes. There are only two routes of any significance to xanthones and these basically involve ring closure on to either the heterocyclic oxygen atom or the carbonyl carbon atom (Scheme 185). 

Insecticidal activity is shown by a number of oxygen heterocycles. Xanthone is an ovicide for the codling moth and the naturally occurring coumarin mammein (713) shows insecticidal properties. 

Although the xanthones contain a ketone oxygen atom, they, like the pyrones (see p. 385), do not react with hydroxylamine, or phenyl hydrazine. 

Both the hetero and carbonyl oxygen atoms of maltol, 3-hydroxy-2-methylpyran-4-one, are replaced by sulfur on treatment with Lawesson s reagent. While the ketone —> thione conversion can be achieved with various sulfur reagents, the heteroatom exchange is unusual and appears specific for Lawesson s reagent (Equation 179). This reaction does not occur with either related chromones or xanthones <2006CC206>. 

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