Benzo xanthone

Chromone carbaldehyde 407 reacts with o-benzoquinodimethane 408 in a Diels-Alder reaction and concomitant deformylation to give a diastereomeric mixture of tetrahydrobenzo[ ]xanthones 409. Subsequent oxidation provides benzo[ ]xanthones 410 in good yields (Scheme 67) <2002T997>. 

Chromone-3-carbaldehydes undergo Diels-Alder reactions with ort o-benzoquinodimethane 819 and deformyla-tion to yield initially benzo[b]-1,6,6a, 12a-tetrahydroxanthones 820, which are easily transformed into their corresponding benzo[ ]xanthones upon treatment with I2-DMSO (Scheme 232) <2002T105>. 

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>. 

Jang and McDow (1997) studied the photodegradation of benzo[a]anthracene in the presence of three common constituents of atmospheric aerosols reported to accelerate benzo [a] anthracene, namely 9,10-anthroquinone, 9-xanthone, and vanillin. The photo-degradation experiments were conducted using a photochemical reactor equipped with a 450-W medium pressure mercury arc lamp and a water bath to maintain the solution temperature at 16 °C. The concentration of benzo [a] anthracene and co-solutes was 10" M. Irradiation experiments were conducted in toluene, benzene, and benzene-c/e- Products identified by GC/MS, FTIR, and NMR included benzo[a]an-thracene-7,12-dione, phthalic acid, phthalic anhydride, 1,2-benzenedicarboxaldehyde, naphtha-lene-2,3-dicarboxylic acid/anhydride, 7,12-dihydrobenzo[a]anthracene, 10-benzyl-10-hydroan-thracen-9-one, benzyl alcohol, and 1,2-diphenylethanol. 

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. ° ... 

Interest in the antibiotic bikaverin (531), a fungal metabolite with a benzo[Z>]xanthone skeleton, has culminated in its total synthesis (76JCS(Pl)499). The chromone moiety (530) was constructed as shown and the xanthone was obtained by cyclization of the acid chloride (Scheme 196). 

Ketones derived from pyrans are called pyranones (also commonly pyrones), and the parent compounds are pyran-2-one 17 and pyran-4-one 18. Trivial names are used for the related benzo analogs coumarin 19, isocoumarin 20, dihydrocoumarin 21, chromone 22, xanthone 23, and chromanone 24. 

Wood Garciniaxanthone D and 1,4,5-trihydroxyxanthone (Minami et al, 1995). 2,5-Dihydroxy-l-methoxyl xanthone, l-o-methylsympho-xanthone, Garciniaxanthone E, symphoxanthone and subelliptenone A (Minami et al, 1996). A new benzophenone derivative, 2, 3, 6-trihydroxy-2,4-dimethoxy-benzo-phenone and a new xanthone, 1,6-0-... 

A change in the pA -order has nevertheless emerged in a different class of compounds xanthone and several substituted benzo-phenones have pA(Tj )-values lying outside the range between pA(S0) and pA(St) (Ireland and Wyatt, 1972, 1973). In these... 

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>. 

TCBTs are relatively persistent and non-flammable (and therefore useful in hydraulic oils). Pyrolysis in a closed system for two days in the presence of hydrogen peroxide at 300 °C produced as main components chlorinated benzo-phenones, fluorenes, fluorenones, xanthenes, and xanthones. Polychlorodiben-zofurans (PCDF) and polychlorodibenzo-p-dioxins (PCDD) were formed in much lower concentrations than from PCB product Pyralene T1 under identical conditions [84]. In pyrolysis at 450-700 °C with excess oxygen TCBTs produce more PCDFs and PCDDs. In parallel with the behavior of PCBs, PCDFs are formed in significantly higher amounts than PCDDs from PCBTs [86],... 

The rearrangements of phenols which are accompanied by hydroxy group transpositions are called the Wessely-Moser reaction (equations 50 and 51). In essence, these rearrangements are recyclizations of flavonoides 114 via the ring-opened form 115 to give the novel structures 116. Compounds that can participate in these rearrangements are flavones (114, R = H, R = Aryl), flavonoles (114, R = OH, R = Aryl), isoflavones (114, R = Aryl, R = H), chromones (114, R = H, R = Alkyl), chromonoles (114, R = OH, R = Alkyl), xanthones (114, R R = benzo) as well as benzopyrylium salts (e.g. see Reference 95). 

Generation and trapping of radical cations of a,co-diphenylpolyenes within the channels of pentasil zeolites provides an environment which allows these transient species to be spectroscopically characterized . Similarly, complexation of xanthone in cyclodextrin has made it possible for the triplet state of this molecule to be fully characterized . Association and dissociation processes are related to the dipoles developed in the complex and in solution. A unimodal Lorentzian lifetime distribution for 2-anilinonaphthalene-6-sulphonate B-cyclodextran inclusion complexes have been recovered by multifrequency phase-modulation fluorometry in the presence of the quenchers Cu, acrylamide, and I . Both the fluorescence and phosphorescence spectra of benzo[f]quinoline adsorbed on p-cyclodextrin/NaCl have been determined as a function of temperature . 

Benzo[b]xanthone formation in 74% yield occurred readily in the reaction of ethyl salicylate and 1-naphthol at elevated temperature in refluxing diphenyl ether during 8 hours (ref.93). 

Xanthones are benzo-7-pyrone derivatives. Plant derived xanthones are of mixed shikimate-acetate origin. Mangiferin, a C-glycosyl xanthone present in the Hypericum species possesses anti-inflammatory, anti-hepatotoxic, and anti-viral properties. 

Studies in the laboratory of Tanaka toward the synthesis of bikaverin 20, a fungal metabolite with a benzo-xanthen skeleton, led to the discovery of an elegant method to form ring C. Upon treatment with aqueous oxalic acid, benzopyranone 16 was directly transformed into xanthone 17, which could be potentially elaborated intro bikaverin 20. The unexpected formation of intermediate 17 could be explained by the following sequence hydrolysis... 

Brnm.xanthon 17 II380. x-Bram-[3.4-benzo-camarin] 17, 360. 

IIitro-3.phenyl- amaraa 17134. Xanth(m.cail>one4uK-(2).amid 18II341. Xanthon- arbona [Pg.825]

FlnoreDon-[4.o -aiiil] 18 1156. Xanthon-aw i, 356. 4.Imiiu>.2.phenyI-7.8-benzo-l. 4-chTomen 171216. 

Benzoyloxy-fIaorenon 9,153. 3 BenzoyIoxy.fluorenon 9, 153. 3 Benzoyl-7.8.benzo.cnmarin 17 II 513. 2.Benzoy] Xanthon 17, 544. 

Amino-xanthon 18, 613. x-Amino-xanthon 18 1 572. S-Amino-T.S-benzo-oumarin 18 II466. x-Amino-. 6-benzo-oumarin 18 II 466. Cubazol-X-oarbons uxe 20 1165. 9-Oxy-aoridin-N-oxyd 211228, 312. t.3-Dioxy.aoridin 21,186, II1. ... 

Acetoxy-2.3>boizo-xantKoa 18 1 334. 6 Acetoxy [benzo-1 2 3.4-xaiitiioii] 18, 66. 5" Acetoxy [benzo 1 2 1.2 xanthon] Oder 4 Acetoxy-[benzO l. 2 2.3-xanthoii]... 

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