Pyrones, phenyl

In the hands of Collie and Tickle in 1899 this reaction gave the first crystalline pyrylium salts. The salt character of the compounds was proved by conductivity measurements the basicity of 2,6-dimethylpyrone was found to be a little higher than that of urea. Basicities of other pyrones decrease in the order 2,6-dimethyl-> 2-phenyl-6-methyl-> 2,6-diphenylpyrone, paralleling the dipole moments. These hydroxypyrylium salts hydrolyze in water to pyrones. " The formation of salts of 2,6-dimethylpyrone with organic acids was investigated by Kendall,and with mineral acids by Cook. 11 ... 

The Baccatin III synthesis by K. C. Nicolaou and co-workers is summarized in Scheme 13.54. Diels-Alder reactions are prominent in forming the early intermediates. In Step A the pyrone ring served as the diene. This reaction was facilitated by phenyl-boronic acid, which brings the diene and dienophile together as a boronate, permitting an intramolecular reaction. 

A derivative of the oxo form of a 3-hydroxyselenophene has been obtained by a quite different route.123 1,5-Diphenyl-1,4-pentadiyn-3-one (94) adds hydrogen selenide and gives a mixture of 2,6-diphenyl-1-seleno-y-pyrone (95) and 2-benzylidene-3-oxo-5-phenyl-2,3-dihydroselenophene (96). 

Interestingly, cyclopropenone exhibited comparable reactivity towards sulfur ylide 437 and phosphorus ylide 439 giving rise to 6-phenyl-2-pyrone and a-naphthol, respectively197. Again, the intermediacy of ketenes 438f440 may reasonably explain the formation of these products. 

Intramolecular electrophilic aromatic substitution to give tricyclic products 142 is also a viable process, with trapping efficiency related to the electron density of the arene trap (equation 3)67. With a simple phenyl group pendant, rearrangement to the 2-pyrone was... 

Pyridine, 1,2,3,4-tetrahydro-l-methy1-2-phenyl-, 54, 93 a—Pyrone, irradiation of, 50,... 

Diese Reaktionsart ist bei den Addukten aus Butadien-carbonsaure-Derivaten mit der Carboxylgmppe in 3-Stellung allein verwirklicht dabei entstehen 3-Amino-a-pyrone [58, 70, 72). So geht das N-p-Chlorphenyl-3-methoxycarbonyl-6-phenyl-3.6-dihydro-1.2-oxazin bei der Chromato-graphie an Aluminiumoxid in 3-p-Chloranilino-6-phenyl-a-pyron uber (55), der Mechanismus ist analog dem der Pyrrolbildung. 

LC UV is valuable for the identification of isoflavones since their spectra differ in absorption properties from most of the other flavonoids. They have a C2-C3 double bond, with the B-ring at C3, which prevents conjugation of the phenyl group with the pyrone carbonyl group. This reduces the contribution of the B-ring to the UV spectrum and results in a peak of very low intensity in the 300 to 330 nm range (band I). 

Dimethoxy-6-phenyl-2//-pyran (274) with sodium hydroxide in DMF provided 34% of 6-phenyI-2-pyrone (S42).295... 

In benzo- and phenyl-pyridines and in phenylpyridine 1-oxides, electrophilic substitution usually takes place in the benzene ring. In benzo-pyridones, -pyrones and -pyridine A-oxides, electrophilic substitution often occurs in either the benzene or the heterocyclic ring depending on the conditions sometimes mixtures are formed (see Section 3.2.3.2.1). 

Nitration of 6-phenyl-2-pyrone (87) depends on the conditions. The free base reacts at the 3-position, the conjugate acid at higher acidities in the p-position of the phenyl group. 

Halogen atoms in pyrones and pyridones e.g. 902) are unreactive toward SAE nucleophilic displacement. 3-Halopyridines are less reactive than the a- and 7-isomers but distinctly more reactive than unactivated phenyl halides. Thus, a bromine atom in the 3-position of pyridine or quinoline can be replaced by methoxy (NaOMe-MeOH, 150°C), amino (NH3-H20-CuS04, 160°C) or cyano (CuCN, 165°C). 5-Halogens in pyrimidines are also relatively unreactive. 

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). 

Although the xanthones contain a ketone oxygen atom, they, like the pyrones (see p. 385), do not react with hydroxylamine, or phenyl hydrazine. 

The method described is that of Miles, Harris, and Hauser2 and is an improvement over the earlier procedure of Hauser and co-workers.3,4 In the earlier method the dianion of benzoylacetone, formed by the action of alkali amide in liquid ammonia, was treated with methyl anisate to yield 1 -(/>-methoxyphenyl)-5-phenyl-l,3,5-pentanetrione (61% based on the ester). This compo ir d has also been prepared by the base-catalyzed ring opening of 2 - f -mcthoxyphenyl) -6-phenyl -4 pyrone however, no yield is reported.5... 

METHOXYPHENYL)-6-PHENYL-4-PYRONE [4H-Pyran-4-one, 2-( -methoxyphenyl)-6-phenyl-]... 

The method is an adaptation of the procedure of Light and Hauser.2 2-( -Methoxyphenyl) -6-phenyl-4-pyrone has been prepared in 50% yield by a Claisen-type acylation of -methoxy-acetophenone with ethyl phenylpropiolate accompanied by cyclization.3... 

This procedure offers an extremely simple and fairly general method for the preparation of 2,6-disubstituted 4-pyrones. Pyrones which have been prepared2 by this procedure are 2-methyl-6-phenyl-4-pyrone (60%), 2-(J>-chlorophenyl)-6-mcthyl-4-pyrone (90%), 2,6-diphenyl-4-pyrone (91%), 2-( -chloro-phenyl)-6-phenyl-4-pyrone (90%), 2-phenyl-6-(3-pyridyl)-4-py-... 

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