Heterocycles xanthones

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. 

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. 

Hano, Y. et ak. Components of the root bark of Morus insignins. 3. Structures of three new isoprenylated xanthones morusignins I, J and K and an isoprenylated flavone morusignin L., Heterocycles, 36, 1359, 1993. 

The Balz-Schiemann synthesis can be applied not only to substituted anilines but also to aminobiphcnyls1,131 or amino-substituted fused polyaromatic compounds, such as naphthalene,1114,119,129 anthracene,136 phenanthrene,1135 acenaphthene,133 fluorene,1,131,134 benzanthracene,130 136 pyrene,136 chrysene,136 fluoranthene,131 fluorenone,1,131 anthra-quinone,1,137,139,140 benzanthrone,1,117,118 phenanthraquinone,138 or xanthone.132 Fluorinated pyridines,1,141"146 methylpyridincs,126,147 149 pyridinecarboxylic acids,150 quinolines,1,151 isoquinolines,152 quinazolone,1 thiazoles,153,154 isothiazoles,156 benzothiazoles,157 thiadiazoles,155 and thiophenes154 can also be obtained from the corresponding aminated heterocycles. Modified Balz-Schiemann methods are recommended for amino nitrogen-containing heterocycles, the diazonium salts of which are rather water-soluble and unstable (a violent explosion was reported for pyridine-3-diazonium tetrafluoroborate).159 These new techniques have also been specially adapted for pyrazol-, imidazol-, or triazolamines which fail to react under classical conditions.158... 

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). 

Interesting transformations occur in systems where the cyclohexa-2,5-dienone fragment is in a spiro connection with heterocycles. Thus, treatment of griseofulvin derivative 317 with magnesium iodide results in the xanthone derivative 318 via a dienone-phenol rearrangement (equation 152). 

Palladium migration is a mechanistically interesting and synthetically useful process, because it provides an indirect approach to introduce palladium to a specific location in an organic molecule. It also allows C-H activation to occur on a remote site whose direct functionalization may not be easily achieved. Through the years, palladium migration processes have been applied to the construction of a variety of important heterocycles, such as carbazoles [25, 26], indoles [26], xanthones [27], and fluoren-9-ones [27, 28], They have also received special attention from computational chemists, who have conducted theoretical studies on the mechanism and transition state [29-31],... 

Products of the phenylpropanoid pathway. These compounds, commonly referred to as polyphenols, are derived from cinnamic acid and include the xanthones and flavonoids. The basic structural unit of the flavonoid family (Fig. 1) comprises two benzene rings linked through a heterocyclic pyran or pyrone ring (C ring) variations in the C ring and the extent of hydroxylation define the major classes [4]. 

The iron-catalyzed synthesis of dihydro-2H-pyrans, 2H- and 4H-chromenes, chromones, isocoumarins and xanthenes were described in a broad review on the synthesis of heterocycles (14T4827), while the synthesis of 2H-pyran and chroman derivatives, coumarins and xanthone-type compounds was described in a review of recent progress on the chemistry of dimethyl acetylenedicarboxylate (14S537). The synthesis of several polysubstituted spirooxidole-2-amino-4H-pyrans, mainly through three-component reactions, was also described in a review on the synthesis of biologically active spirooxindoles (14T9735). 

Heterocyclic compounds containing oxygen include many phenolic compounds, particularly flavonoids, the most important pigments of which are anthocyanins related to pigments derived from isochromene and xanthone. 

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, ... 

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