Simple xanthone

Simple xanthones include various mutagenic and antibacterial compounds such as bellidifolin (3-methoxy-l,5,8-trihydroxyxanthone). A number of simple xanthones are inhibitors of monamine oxidase A (bellidifolin, demethylbellidifolin, gentiacaulin, isogen-tisin and swerchirin), protein kinase (norathyriol) and of xanthine oxidase (athyriol, isoathyriol and norathyriol). 

It is difficult to synthesize 9-[l-(2,4,6-cycloheptatrienyl)]-9-xanthydrol [347] from xanthone by a simple addition, considering the potential nucleophile, cyclohepta-trienide anion, is antiaromatic. An umpolung strategy works well in that reversed roles are given to the two reactants. 

The mechanisms of these two cyclization reactions appear fairly different. While the xanthone synthesis would appear to follow a simple palladium migration/arylation mechanism, the fluoren-9-one synthesis has been subjected to isotope labeling experiments (Scheme 12), which indicate that more than one mechanistic pathway may apply. It turns out that the deuterium that replaces the iodide after palladium migration comes not only from the imidoyl position, but also from the pendent aromatic ring used to trap the migrated palladium via arylation. Such results can... 

Using xanthone as the sensitizer, Navaratnam et al. (1985) calculated the molar absorption coefficient of benoxaprofen triplet-triplet absorption in aqueous solution at 410 nm as 17,500 dm3 mol1 cm. In this case this simple treatment was possible because... 

Simple symmetrical homodimers of chromenes with a C-C linkage such as ageratoriparin and non-symmetrical ones with an ether bond, like pterochromene 13 are both known. Chromones can form homodimers, such as compound D-1580, or combine with a flavonoid as in the case of compound D-1419. Ergoxanthine is better considered as a xanthone precursor rather than a proper chromanone. (Scheme 22). ... 

Lei and his associates developed a Pd-catalyzed double C-H functionalization/ carbonylation of diaryl ethers to form xanthones [45]. By using a simple catalytic system consisting of Pd(OAc)2, K2S2O8, and TFA, a variety of diaryl ethers could be directly carbonylated to xanthones in moderate to good yields (Scheme 6.13). Moreover, various functional groups were tolerated under the optimized conditions. Notably, this transformation provides an effective and practical protocol for the syntheses of bioactive xanthones. 

With a basic skeleton of Q, there are simple phenols and benzoquinones with C -Ci structure, there are hydroxyben-zoic acids such as gallic acid corresponds to pheny-lacetic acids and with C -C skeleton there is a larger class including hydroxycinnamic acids, coumarines, and chro-mones. Sometimes these strucmres appear dupUcated, giving rise to lignoids. Naphthoquinones have a C6-C4 stmcmre, while xanthones exhibit a Ce-Ci-Cg one. Stilbenes and anthraquinones are Cg-Ca-Ce compounds. 

Nonflavonoid compounds comprise simple phenols, phenolic acids, coumarins, xanthones, stilbenes, lignins, and lignans. Phenolic acids are further divided into benzoic acid derivatives, based on a C6-C1 skeleton and cinnamic acid derivatives, which are based on a C6-C3 skeleton [6], The conmarins are phenolic acid derivatives composed of a benzene ring fnsed with an oxygen heterocycle. Xanthones consist of a C6-C1-C6 basic structure, and stilbenes are composed of a C6-C2-C6 skeleton with various hydroxylation patterns [13], Lignins are polymers of C6-C3 units, whereas lignans are made up of two phenylpropane units [13]. The structures of each of these classes are shown in Table 16.1. 

There are several ways in which phenols have been categorized. Harbome and Simmonds categorized polyphenols based on the number of carbon atoms, which includes simple phenols (Ce) phenolic acids and related compounds (Ce—Ci) acetophenones and phenyl acetic acids (Cg—C2) cinnamic acids, cinamyl aldehydes, and alcohols (Cg—C3) coumarins, isocoumarins, and chromones (Cg—C3) flavonoids (C15) biflavonyls (C30) stilbenes (Cg—C2—Cg) benzophenones and xanthones (Cg—C2—Cg) quinones (Cg, Cio, Cm) betacyanins (Cjg) and lignans, lignins, tannins, and phlobaphenes (which are dimmers, oligomers, or polymers) [19]. Polyphenols have also been categorized by some researchers based on their... 

Moreover, according to chemical structure, polyphenols can be divided in classes as simple phenols, benzoquinones, phenolic acids, acetophenones, phenylacetic acids, hrodroxycinnamic acids, phenylpropenes, coumarins, isocoumarins, chromones, naphthoquinones, xanthones, stilbenes, anthraquinones, lignans, neolignans, lignins, and flavonoids. The latter allow to consider 13 subclasses with more than 5,000 compounds (Fig. 74.2). 

Heteroarenes and Benzannulated Heterocycles. The heteroatom arylation methods involving 2-(trimethylsilyl)phenyl triflates have been extended to the preparation of heterocycles. Acridones, xanthones, and thioxanthones are readily obtained by reacting methyl 2-aminobenzoate, methyl salicylate, or methyl thiosalicylate, respectively, with the aryne generated from 2-(tri-methylsilyl)phenyl triflate (eq 8). The ar3me is also used to prepare various benzannulated heterocycles via a three-component coupling process where at least one other cort5)onent is an imine or carbonyl compound. This procedure provides simple entry to racemic substituted benzoitninofurans, 2-iminoisoindolines, ... 

Maleimide. Maleimide and maleic anhydride are simple olefins and very useful molecules in organic syntheses for introducing various substituents. Addition reactions, cyclodimerization, Diels-Alder reactions and polymerization reactions are as well-known as their photochemical reactions. They are also known as electron acceptors in photoinduced electron-transfer reactions. The photosensitized reaction of maleimide with xanthone in 2-propanol has been investigated by TR EPR. The emissive CIDEP spectrum observed in 2-propanol is predominantly assigned to two kinds of maleimide alkyl-type radicals. On the other hand, the absorptive spectrum of the maleimide radical-anion was observed in 2-propanol in the presence of hydrochloric acid. The hydrochloric acid addition effect on the CIDEP patterns indicates the existence of two mechanisms for the photosensitization of maleimide by xanthone. One is a T-T energy transfer to maleimide followed by hydrogen abstraction by maleimide... 

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