Flavone 2-phenyl-4-chromone

Apigenin 4 , 5,7-Tribydraxyflavone or 41,5,7-Trihydroxy-2-pbenylchromone, called in Ger 5.7.4 -Trioxy-flavon or 5.7-Dioxy-2-[4 -oxy-phenyl]-chromon, 0—C- C6H -0H... 

Flavonoids are more or less intensely yellow colored pigments belonging either to the group of 2-phenyl-chromones 39 (flavones, flavonols) or 2-phenyl-chromanones 391 (flavanones, flavanonols) both groups have a backbone of 2-phenyl-l,4-benzopyrones ... 

These are more-or-less intense yellow pigments, with a structure characterized by two benzene cycles bonded by an oxygenated heterocycle, derived either from the 2-phenyl chromone nucleus (flavones and flavonols) or the 2-phenyl chro-manone nucleus (flavanones and flavanonols) (Figure 6.7). 

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... 

The ketones derived from the pyrans are known as pyranones (17) and (18), although the name pyrone has enjoyed much usage. Trivial rather than systematic names are in general use for the benzologues (19), (20) and (21) and these, too, are used throughout. The 2-phenyl derivative of chromone is known as flavone (22). 

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

Dipole moments of flavone (22) and isoflavone (64) have been calculated as a function of the angle by which the phenyl ring is rotated out of the plane of the chromone moiety (B-77MI22200). Correlation of the observed and calculated moments occurs when the ring is turned through less than 30° in the case of flavone, but through approximately 50° for the other flavonoid, and it thus appears that neither molecule is planar. 

In the same manner as acetophenones some other methyl compounds can also be transformed with salts (8) to the corresponding phenyl compounds. 2-Methyl-chromone (19), and likewise 2,6-dimethyl-4-pyrone by double conversion, lead to flavone (20) and 2,6-diphenyl-4-pyrone respectively36. Even the very weak acid methyl groups in methylphenylsulphone and in 6-methylazulene (21) may be smoothly transformed. A 100% excess of (<5) and added sodium methoxide in this... 

Important derivatives of 4i/-chromene are chromone 5 (4//-l-benzopyran-4-one), flavon 6 (2-phenyl-4//-l-benzopyran-4-one) and xanthene 7 (note the exception to systematic numbering). They will be discussed in chapter 6.12. 

The gamma-chromene structure appears in many natural products as derivatives with a 4-keto group. The parent is known as chromone (3.56), and it is found especially in the flavone (flavonoid) family, which has a 2-phenyl substituent. Flavone itself has structure 3.57 and is a yellow solid found in plants. A flavonoid from strawberries, fisetin (3.58), is said to have weak memory-enhancing ability. ... 

Important derivatives of 4H-chromene are chromone (8, 4H-l-benzopyran-4-one), flavone (9, 2-phenyl-4H-l-benzopyran-4-one), and xanthene (10), which are discussed in Section 6.12. 

The reversible ring-deavage of the chromone system to (2-hydroxy)phenyl-l,3-diketones 2 (see above) can also occur on acid catalysis. If an additional OH function is present in the 5-position of the benzo part of chromone, it also can participate in the re-cyclization. Chromones and especially flavones with an unsymmetrically substituted benzene ring undergo isomerization by this route when treated with strong acids (Wesseley-Moser rearrangement), for example, 7 —> 8 ... 

Also related is the oxidative cyclization of 2-aroyl-3-aryl-acrylophenones (166) to 3-acyl-chromones (167) with selenium dioxide in isoamyl alcohol/ Oxidation of 2-phenyl-2H-l-benzopyrans with potassium permanganate provides a new synthesis of flavones/ A radical mechanism has been suggested. 

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