2- Phenyl 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 ... 

The main constituents of flavonoid drugs are 2-phenyl-y-benzopyrones (2-phenyl chromones) or structurally related, mostly phenolic, compounds. 

The application of fluorinated chromones in the synthesis of 1,4-diazepines is exemplihed by reaction of phenyl chromones 97 (Fig. 10.42). ... 

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). 

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

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... 

Grignard reaction, 3, 711 Chromone-2-carboxylic acid, 7-phenyl-ethyl ester reduction, 3, 704... 

Dipolar cycloaddition of 3-cyano-4// -1 -benzopyran-4-thione 187 with benzonitrile oxide proceeded regioselectively to give cycloadduct 188 (involving the thione function). The unstable cycloadduct fragmented to yield 3-cyano-chromone 189 and phenyl isothiocyanate (Scheme 1.32) (355). 

Chromone-3-carbonitrile oxide undergoes cycloaddition reactions with phenyl-and diphenylacetylenes to give isoxazoles 205 (R = H, Ph). The nitrile oxide is obtained from 3-formylchromone oxime by bromination and subsequent dehy-drobromination (175). 

Another problem for the synthetic use of PFR is that the ortho-rearranged products may act as internal light filters, stopping the reaction. In synthetic routes leading to chromanones, chromones, and related compounds, this is of vital importance because the overall yield is limited by the photochemical step. Improved yields can be obtained if the a, 3-unsamrated orr/io-hydroxyphenones resulting from PFR are removed and cyclized to chromanones. This can be acomplished in one pot by irradiation in a two-phase system benzene/10% aqueous NaOH, whereby chromanones are directly obtained from phenyl crotonates in 80-90% yields [210]. 

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)... 

Bond angles and lengths for 3-bromoflavone have been determined <82AX(B)983>. Whilst the two rings of the chromone system are essentially coplanar, the 2-phenyl group is twisted by 45.9° relative to the rest of the molecule apparently the steric interaction between the bromine atom at C-3 and H-2 outweighs the resonance stabilization which would be associated with a completely planar structure. 

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. 

Although there is evidence that chromone syntheses which proceed by the cyclization of phenyl esters under Friedel-Crafts conditions may involve a Fries rearrangement and hence require the formation of one bond adjacent to the heteroatom, syntheses of chromones from phenols will be considered together in this section. The Simonis reaction (530R(7)l)... 

It is pertinent to note that the ester (472) yields a chromone on treatment with hydrogen fluoride (54LA(587)16), suggesting the intervention of a Fries rearrangement once again. The same applies in the formation of 2-chlorochromone from phenyl 3,3-dichloropropenoate <60CR(250)2819). 

Tanaka, T., Orii, Y., Nonaka, G. and Nishioka, I. (1993) Tannins and related compounds. CXXIII. Chromone, acetophenone and phenyl propanoid glycosides and their galloyl and/or hexahydroxy phenoyl esters from leaves of Syzygium aromaticum Merr and Perry. Chemical Pharmaceutical Bulletin 28, 685-687. 

Another interesting reaction is the addition of an enaminoester to phenyl 4-chromone sulphonate, leading to a mixture of fused heterocyclic products in nearly equimolar amounts103 (equation 72). 

The Pd-catalysed Miyaura-Suzuki coupling of aryltrifluoroborates with 4-tosyloxycoumarins in aqueous conditions offers an attractive route to 4-arylcoumarins <06TL1525> and 4-hydroxycoumarins have been converted into a mixture of predominantly thiopyrano[5, 4 3,4]- pyrano[5,6-c]coumarins and [6,5-c]chromones in a one-pot tandem Knoevenagel - HDA sequence with an S-prenylated 1-phenyl-lff-pyrazole-4-carbaldehyde <06TL2265>. The benzopyrano[4,3-c]benzopyranone system can be obtained from 3-aryl-4-methylcoumarins by deprotonation of the methyl function and subsequent elaboration <06TL5909>. 

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