Of xanthone

Colourless crystals m.p. 122 C. It is prepared by reducing an alcoholic solution of xanthone with sodium amalgam. 

Figure Bl.16.19. (a) CIDEP spectrum observed in die photolysis of xanthone (1.0 x 10 M) in cyclohexanol at room temperature. The stick spectra of the ketyl and cyclohexanol radicals with RPM polarization are presented, (b) CIDEP spectrum after the addition of hydrochloric acid (4.1 vol% HCl 0.50 M) to the solution above. The stick spectra of the ketyl and cyclohexanol radicals with absorptive TM polarization are presented. The bold lines of the stick spectra of the cyclohexanol radical show the broadened lines due to ring motion of the radical. Reprinted from [62].

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. 

Xanthhydrol. Prepare an amalgam from 9 0 g. of clean sodium and 750 g. (55 ml.) of mercury (Section 11,50,7, Method 1), and warm it to 50° in a 500 ml. Pyrex bottle. Add a cold suspension of 25 g. of xanthone in 175 ml. of rectified spirit, stopper the bottle and shake vigorously raise the stopper from time to time to release the pressure. The temperature rises rapidly to 60-70°, the sohd xanthone passes into solution, and a transient blue colour is developed. After about 5 minutes the alcoholic solution is clear and almost colourless. Shake for a further 10 minutes, separate the mercury, and wash it with 15 ml. of alcohol. Filter the... 

The results described above represent the first example of the FR mechanism (Scheme 1). Semiempirical calculations on this molecule showed that the intersystem crossing to the excited triplet state is favored The reaction cannot be sensitized by xanthone because the triplet state of 3,4-diphenyl-1,2,5-oxadiazole is lower than that of xanthone. The cleavage of the triplet state to the biradical is favored, considering the relative energy of this intermediate (Fig. 23) (OOOUPl). 

The following example comes from the work of Gottlieb and Kubitzki (1983) on the use of xanthones as indicators of relationships within Gentianaceae, a family... 

The degradation of xanthone by Arthrobacter sp. strain GFBIOO closely resembled the pathways used for carbocyclic compounds. In a yeast-supplemented medium, initial dioxygenation to the 3,4-dihydrodiol was followed by dehydrogenation to 3,4-dihydroxyxanthone and extradiol ring fission to a coumarin and subsequent production of 2,5-dihydroxybenzoate (Figure 10.38) (Chen and Tomasek 1991 Tomasek and Crawford 1986). 

FIGURE 10.38 Biodegradation of xanthone. (From Neilson, A.H. and Allard, A.-S., The Handbook of Environmental Chemistry, Vol. 3J, pp. 1-80, Springer, Heidelberg, 1998. With permission.)... 

Chen C-M, PH Tomasek, RL Crawford (1986) Initial reactions of xanthone biodegradation by an Arthrobacter sp. J Bacteriol 167 818-827. 

Product (41) was also obtained in the presence of xanthone as sensitizer. This product could be totally eliminated by the triplet quencher piperylene, indicating (41) to be derived from the diphenylethylene triplet state. 

Benzophenones and xanthones have the C6-C1-C6 structure. The basic structure of benzophenone is a diphenyl ketone, and that of xanthone is a lO-oxy-10/7-9-oxaanthracene. More than 500 xanthones are currently known to exist in nature, and approximately 50 of them are found in the mangosteen with prenyl substituents. 

A total of 515 xanthones have been identified in 20 families of higher plants, mainly in the Bonnetiaceae and Clusiaceae families (Vieira and Kijjoa 2005). Mangosteen fruit, a typical southeast Asian fruit, is the characteristic dietary source of xanthones (less than 7-8 mg/100 g FW) (Walker 2007). Mangostin is a C-glucosylxanthone that is also found in by-products of mango at high concentration levels (Barreto and others 2008). 

Table 14 Equilibrium constants and association and dissociation rate constants for the ground-state and triplet excited state of xanthone (35) with CDs...

Li JQ, Hu MY, Yao SQ (2009) Rapid synthesis, screening, and identification of xanthone-and xanthene-based fluorophores using click chemistry. Org Lett 11 3008-3011... 

One of the most important developments in the biochemistry and biology of xanthones is surely the recent discovery of their antimalarial activity, and attempts to understand their mode of action. In the last few years, a large number of polyoxygenated, prenylated and non-prenylated xanthones have been reported for their antimalarial activity, and the advance in the understanding of their mode of action has progressed quicker than any other known antimalarials (cf. 14 for a review). 

Kelly JX, Winter R, Peyton DH, Hinrichs DJ, Riscoe M. (2002) Optimization of xanthones for antimalarial activity The 3,6-bis-co-diethylaminoalkoxyxanthone series. Antimicrob Agents Chemother 46 144-150. 

Salicylic [186] and thiosalicylic [187] acid derivatives can also be subjected to PFR, providing straightforward entries to the synthesis of xanthones and thiox-anthones (Scheme 66). 

Mixtures of xanthone (246) and 3,4-benzocoumarin (247) result when 2-aryliodoniobenzoates 245 are heated at higher temperature. This reaction involves fragmentation of 245 to benzyne, carbon dioxide, and iodoarene. Thus, in the absence of trapping agents, the benzyne intermediate reacts with 245 to form cyclized products 246 and 247 (64JOC1637) (Scheme 63). 

Scheme 4.13 (a) Two different types of xanthone-based oxyanion hole receptors developed by Simon and co-workers and (b) possible mode of catalysis of a conjugate addition reaction between pyrrolidine and a, 5-unsaturated valerolactam by one of the receptors. 

When 2 -methoxy-2-biphenylamine is diazotized in fluoroboric acid, an 85% yield of solid 2 -methoxy-2-biphenylyldiazonium tetrafluoroborate is produced. On heating in dry benzene, this salt loses nitrogen and provides 0-methyldibenzofuranium tetrafluoroborate as an unstable solid. The latter salt, on account of the low basicity of dibenzofuran, reacts with a range of nucleophiles that undergo methylation with the release of dibenzofuran. Pyridine and pentachloropyridine are N-methylated, benzo[fc]thiophene is S-methylated, and tetrahydrofuran and phenetole are 0-methylated. ° Thus it is no surprise that diazotization of 2 -methoxy-2-biphenylamine, followed by boiling of the diazonium salt in acidic solution, provides dibenzofuran in 90% yield.The scope of this method of dibenzofuran synthesis (Scheme 18) has been little explored probably because of the difficulty of preparing the requisite biphenyls, which is usually accomplished by a crossed Ullmann reaction. A similar synthesis of xanthones from 2-amino-2 -methoxybenzophenones is known. ° ... 

Research Focus Synthesis of xanthone copolymers for use as electroactive components in thin films. 

Originality Photovoltaic components consisting of xanthone polymers have not been... 

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

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