4-Flavones

2 Synonyms. 2-Phenyl Chromone 2-Phenyl-y-benzopyrone 2-Phenyl-l, 4-benzopyrone. 

However, the relatively simpler two-step s3mthesis for FLAVONE shall be discussed in the sections that follow  

Equation (a) o-Hydroxyacetophenone on benzoylation with benzoyl chloride in the presence of basic medium due to the presence of p3rridine gives rise to the formation of o-benzoyloxy-acetophenone, and a mole of hydrochloric acid is liberated. The liberated HCl instantly combines with the P3rridine (basic) present in the medium to 3ueld the corresponding 

Equation (6) The o-benzoyloxyacetophenone on heating and treatment with freshly distilled anhydrous glycerol, in an absolute inert atmosphere, abstracts a mole of water and ultimately undergoes cyclization to 3neld flavone. 

Recrystallization. The crude product is recrystallized finm 15 ml of methanol, and the pure white crystals of or /io-benzoyloxyacetophenone (mp 76.5-77.5°C) is obtained between 9-9.5 g. 

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It may be regarded as the parent of a number of important classes of compounds derived from the y-pyrone skeleton (e.g. flavone, xan-thone) and the important chroman derivatives called the tocopherols (vitamin E). 

C. Insoluble in water, soluble in organic solvents. Flavone occurs naturally as dust on the flowers and leaves of primulas. It has been prepared from o-hydroxyacetophenone and benzaldehyde. 

Phenolic oxygen participates in facile oxypalladation. The intramolecular reaction of 2-hydroxychalcone (105) produces the flavone 106[127]. The ben-zofuran 107 is formed from 2-allyIphenol by exo cyclization with Pd(OAc)2, but benzopyran 108 is obtained by endo cyclization with PdChf S], Normal cyclization takes place to form the furan 109 from 2-(l-phenylethenyl)phe-nol[129]. Benzofuran formation by this method has been utilized in the synthesis of aklavinione (110)[130]. 

Flavone [525-82-6 Flavone dyes Flavone synthase Flavonoids... 

PyrogaHol (1) was first observed by Scheele in 1786 as a product of the dry distillation of gaUic acid [149-91-7] (3,4,5-ttihydroxybenzoic acid). PyrogaHol, which is of widespread occurrence in nature, is incorporated in tannins, anthocyanins, flavones, and alkaloids (1). 

Phloroglucinol (42) is a colorless and odorless solid which is only spariagly soluble ia cold water (82). It was discovered ia 1855 ia the hydrolysis products of the glucoside phloretia, which was obtained from the bark of fmit trees. Phlorogluciaol occurs ia many other natural products ia the form of derivatives such as flavones, catechins, coumaria derivatives, anthocyanidins, xanthins, and glucosides. 

Glycosides, particularly of phenoHc compounds, are widely distributed in plant tissues (2,10). Glycosides of anthocyanidins, flavones, flavanols, flavanones, flavanonols, stilbenes and saponins, gaUic acid derivatives, and condensed tannins are all common. 

Flavones. These compounds are the most widely distributed natural coloring matter formerly used as dyestuffs. The term flavone was first suggested in 1895 (69), and is indicative of their yellow color ijlavus, Latin for yellow). They have lost their commercial value as dyes since the advent of synthetic dyes in 1856. 

Flavone-type dyes occur in all the higher plants in the leaves, roots, bark, fmits, poUen, and flower petals. None have been found in fungi, mosses, or hchens. The most widespread flavone dyes are quercetin [117-39-5] (12) and kaempferol [520-18-3] (13) ... 

In general, the dyes occur as glycosides, the most common sugar being glucose. Some flavones contain more than one sugar. Their role as dyes in the plant is not definitely known a common suggestion is that they protect the plant from harm fill uv radiation. 

The basic unit of the flavone-type dyes is 2-phenyIbenzopyrone (14) which unsubstituted is flavone [525-82-6], isoflavone [574-12-9] is (15) and flavonol [577-85-5] is (16). 

Flavone dyes having these stmctures are hydroxylated and methoxylated derivatives. The degree of hydroxylation varies from two in chrysin [480-40-0] (17) to six in gossypetin [489-35-0] (18). Those dyes containing not more than three hydroxyls are generally termed flavones whereas those containing up to and including six are flavonols. 

The flavone, isoflavone, and flavonol-type dyes owe their importance to the presence of an o-hydroxy carbonyl stmcture within the molecule. Positions 4 and 5 can chelate with different metallic salts to give colored, insoluble complexes. In other words, these dyes require a mordant in order to fix them onto the fiber. Perkin was able to predict the stmcture of unknown flavones by comparing the color of their complexes with the color of known complexes (70). For example, ferric chloride gives a green color with 5-hydroxyflavones and a brown one with 3-hydroxyflavones (71). 

Chrysin (17) was the first flavone to be isolated in a pure form, and its stmcture was elucidated by identification of its alkaline degradation products (72—74). The stmcture was confirmed by synthesis (75,76). The same procedures were used to estabflsh the stmcture of other flavones and in so doing the foundation of flavone chemistry was laid (77). 

Benzo[/]flavone conformation, 3, 623 Benzo[g]flavone conformation, 3, 623 Benzofuran fluorinated... 

H-l-Benzopyran-4-ones — see Chromones 4H-l-Benzopyran-4-ones, 2-phenyl — see Flavones Benzopyranopyrazoles synthesis, S, 317, 341 Benzopyrano[4,3-c]pytazol-4-one synthesis, 3, 712 Benzopyrano[4,3-6]pyridine synthesis, 3, 712 Benzopyrano[4,3-ii]pyrimidine synthesis, 3, 712 Benzopyrans nomenclature, 1, 23 pyrylium salt synthesis from, 3, 873 reactions... 

Ceroplastol synthesis, 1, 428 Cetyl alcohol synthesis, 1, 478 Chaetoglobasins structures, 4, 376 Chalcone, o -azido-2 -oxy-synthesis, 3, 823 Chalcone, 2-hydroxy-reduction, 3, 751 Chalcone, 2 -hydroxy-mass spectra, 3, 618 Chalcone dibromides flavone synthesis from, 3, 823 Chalcones polymers, 1, 304 Chanoclavine synthesis, 6, 423 Charge density waves in stacks of ions, 1, 351-352 Chartreusin... 

Kojic acid — see also Pyran-4-one, 5-hydroxy-2-hydroxymethyl-, 3, 611 acylation, 3, 697 application, 3, 880 occurrence, 3, 692 reactions, 3, 714, 715 with amines, 3, 700 with phenylhydrazine, 3, 700 synthesis, 3, 810 Kokusagine occurrence, 4, 989 Kokusaginine occurrence, 4, 989 synthesis, 4, 990 Koopmans theorem, 2, 135 Kostanecki-Robinson reaction chromone and coumarin formation in, 3, 819-821 mechanism, 3, 820 flavones, 3, 819... 

BAKER VENKATARAMAN Flavone synthesis Rearrangement of aromatic keto esters ot phenols to tiavones... 

Flavone (2-phenyI-4ff-l-ben2opyran-4-one) [525-82-6] M 222.3, ni 100°. Crystd from pet ether. 

Rhamnetin (3,3 -4, 5-tetrahydroxy-7-methoxy flavone, 7-methyl quercitin) [90-19-7] M 316.3, m >300"(dec), several phenolic pKs -7-10.5. Crystd from EtOH. 

Rutin (quercetin-3-rubinoside) [I53-I8-4J M 610.5, m 188-189, [a]54g+13° (c 5, EtOH) (polypbenolic flavone pKs 7—10). Crystd from MeOH or water/EtOH, air dried, then dried for several hours at 110°. 

Sesquiterpenes and flavonoids (flavones, flavanones, flavanes) are two elasses of natural substan-ees which occur frequently in plants and whieh have 15 C atoms in their framework. The nine... 

Flavone, cumann and tnterpene glycosides, solamargine, solasomne... 

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