4-Pyrone 2- -6-phenyl-, ring

A family of pyrones with polycyclic substituents at C-6 has been identified (83TL5373 85TL2453 89CC1284) and named solanopyrones A, B, C, and D (134-137). Solanopyrone C is most unusual in that its substituent at C4 is not found in natural products. Further confirmation of its natural origin would be of interest. Compounds 96 and 99 exhibit a nitro group at a phenyl ring. Other structural types frequently encountered are pyrones with substituted benzyl groups at C3 such as 78,110,115, and 116-119 ... 

Attention then shifted to the 6-position of the pyrone molecule. Variation of the substituents on the phenyl ring at C-6 resulted in a series of derivatives with improved enzyme activity. More specifically, the... 

Flavonoids have low molecular weight and occur naturally as aglycons, glycosides and methylated derivatives. The aglycons generally consist of a benzo-(-pyrone which in the position 2 or 3 is substituted by a phenyl ring (Fig. 1). 

Oxazolino-a-pyrone (487) was obtained in five steps starting from 3-benzo-yloxy-2,4-pentanedione (486). Catalytic hydrogenation of487 afforded two products with the same threo stereochemistry 3-benzamido-S-caprolactone (488) and an analogous compound (489) having the phenyl ring peihydrogenated. With... 

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. 

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). 

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). 

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... 

Some recent synthetically useful examples of cyclizations that yield five-membered rings are illustrated below. They include cyclizations onto neighboring phenyl, pyrone, and indole rings ... 

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