Xanthones xanthenes

Commercial PCB mixtures frequently contain impurities that may contribute to the 2,3,7,8-TCDD toxic equivalency factor. These impurities may include other PCBs, dioxins, dibenzofurans, naphthalenes, diphenyl ethers and toluenes, phenoxy and biphenyl anisoles, xanthenes, xanthones, anthracenes, and fluorenes (Jones etal. 1993). PCB concentrations in avian tissues sometimes correlate positively with DDE concentrations (Mora et al. 1993). Eggs of peregrine falcons (Falco peregrinus) from California, for example, contained measurable quantities of various organochlorine compounds, including dioxins, dibenzofurans, mirex, hexachlorobenzene, and / ,//-DDE at 7.1 to 26.0 mg/kg FW PCB 126 accounted for 83% of the 2,3,7,8-TCDD equivalents, but its interaction with other detectable organochlorine compounds is largely unknown (Jarman et al. 1993). 

K. Okuma, A. Nojima, N. Matsunaga, K. Shioji, Reaction of benz)me with salicylaldehydes general synthesis of xanthenes, xanthones, and xanthols, Org. Lett 11 (2009) 169. 

Colourless crystals m.p. 174 C. It is obtained by the action of heat on phenyl salicylate. It may be reduced to xanthene. It is the parent substance of the xanthone group of dyestuffs. 

Maeda K, Terazima M, Azumi T and Tanimoto Y 1991 CIDNP and CIDEP studies on intramolecular hydrogen abstraction reaction of polymethylene-linked xanthone and xanthene. Determination of the... 

Benzo[ifc,/]xanthenes result from the chromium-mediated benzannulation of the carbene complex (20) <96CC895>, whilst the photooxidative cyclisation of ( )-2-styrylchromones (21) leads to benzo[a]xanthones <96HCM251>. 

Moro-Oka et al. (1976) have reported that the oxidation of 9,10-dihydroanthracene by K02 solubilized in DMSO by 18-crown-6 gives mainly the dehydrogenated product, anthracene. Under the same conditions, 1,4-hexadiene is dehydrogenated to benzene. The authors proposed a mechanism in which the superoxide ion acts as a hydrogen-abstracting agent only. The oxidations of anthrone (to anthraquinone), fluorene (to fluorenone), xanthene (to xanthone) and diphenylmethane (to benzophenone) are also initiated by hydrogen abstraction. 

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... 

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. 

Xanthene [92-83-1] M 182.2, m 100.5°, b 310-312°/760mm. Crystd from benzene or EtOH. 9-Xanthenone see xanthone. 

Chromone (4 H-1 -benzopyran-4-one) (21) Xanthone (9H-xanthen-9-one) (22) Flavone (2-phenyl-4 W-1 -benzopyran-4-one)... 

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. 

The use of a quaternary ammonium hydroxide as a phase transfer catalyst provides an efficient conversion of xanthene (174) to xanthone under mild conditions (77TL2117), while the use of permanganate under milder conditions than those shown in Scheme 9 enables flavenes such as (175) and (176) to be converted into flavones (77BCJ3298, 78BCJ1175). The phase transfer oxidation requires strongly alkaline conditions which may render it less suitable for the oxidation of flavenes and chromenes. Xanthene has also been converted into xanthone by means of permanganate or chromic acid. 

Electrophiles attack xanthene at C-2 and sometimes also at C-7 when conditions are sufficiently vigorous. Nitric acid simultaneously oxidizes xanthene to the xanthone and thus gives 2-nitroxanthone. Friedel-Crafts acetylation of xanthene gives either 2-acetyl- or 2,7-diacetylxanthene according to the temperature (0 or 18 °C) and the proportion of acetyl chloride (74BSF2963). 

When xanthone is irradiated in methanol or benzene it is reduced to xanthene, but in cyclohexane 9-cyclohexylxanthydrol is formed. In hexane, the dimeric 9,9 -dihydroxydixan-thene (368) is produced (66BCJ1694). Irradiation of xanthone using a nitrogen laser shows a strong solvent dependence (80JA7747). 

Xanthone is unreactive towards hydrazine and phenylhydrazine. The oxime is obtained by reaction of xanthione (xanthene-9-thione) with hydroxylamine, or from xanthone and hydroxylamine in pyridine. When the oxime is heated in water with phenylhydrazine, the phenylhydrazone is formed. In acid solution, xanthone reacts normally with 2,4-dinitro-phenylhydrazine but xanthone-1 -carboxylic acid (435) gives the pyridazinone (436), possibly via the hydrazone (57JCS1922). When the oxime is heated with phosphorus pentachloride it undergoes a Beckmann rearrangement to give the amide (437) (70MI22300). 

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). 

Xanthene reacts differently with alkynes to give mostly the 9-xanthylidene derivative (462) and a small amount of its cyclized analogue (463) (73RTC845). The spiran (464) is formed in 15% yield when xanthone and l,3-diacetylimidazol-2-one or its homologues are irradiated in acetone (67CB3961). 

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). 

E)-2-Styrylchromones undergo photooxidative cyclization to afford 12//-benzopz]xanthen-12-ones in moderate yield (Equation 337) <1998EJO2031, 1996F1C0251>. 2-Vinyl chromones undergo [4+2]-cycloaddition reactions with enamines to form the intermediates 812, which afford xanthones upon elimination of pyrrolidine (Scheme 228) <2000J(P1)3732>. 

Dimethyl-3/7-xanthen-9(477)-one 817 undergoes a [4+2] cycloaddition with DMAD to form the intermediate 818. Expulsion of isobutene from the initial adduct 818 affords xanthone-3,4-dicarboxylate in good yield (Scheme 231) <1998J(P1)1547>. 

Benzo[fe]xanthene-6,l 1,12-triones are readily available through the photo-induced 1,4-acylation of naphthoquinone with 2-hydroxybenzaldehydes followed by oxidation <02H(57)1915>. Chromone-3-carboxaldehyde reacts with o-benzoquinodimethane in a DA reaction with concomitant deformylation to give a diastereoisomeric mixture of tetrahydrobenzo[fc]xanthones oxidation can be accomplished with DMSO/I2 <02T105>. 

So konnten in einer Studie in Schlammen aus Zellstoffwerken alkylierte Polychlor-dibenzofurane nachgewiesen werden [Buser et al. 1989]. Unter okotoxikologischen Aspekten besonders relevant erscheinen in diesem Zusammenhang auch die polychlo-rierten Xanthene und Xanthone, die mit den PCDD auch hinsichtlich der massen-spektrometrischen Bestimmung interferieren konnen [Kuehl et al. 1987]. 

Intramolecular cyclisation following halogen-metal exchange in the benzonitrile derivatives 25 provides a route to xanthones and thioxanthones. Incorporation of a second aryl halide function into the benzonitrile substrate allows an anionic cascade ring-closing sequence and the formation of pentacyclic xanthene derivatives 26 <03JOC4091>. 

The anion derived from furobenzopyrandione 28 reacts with Michael acceptors regiospecifically to yield xanthones and various annulated derivatives <03OL3753> and intramolecular trapping of the anion by a carbamate side-chain leads to spiro- pyrrolidine and piperidine 9-xanthene derivatives <03TL9291>. 

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