2H-1-Benzopyrans

Dihydro-6-methyl-4-phenyl-2H-benzopyran-2-one (100.0 g, 420.2 mmol) is added to toluene (500 ml). The mixture is degassed by purging alternately with vacuum and nitrogen and then cooled to -21°C. Diisobutylaluminum hydride in toluene solution (DIBAL, 1.5 M, 290 ml, 435 mmol) is then slowly added over 2 h via add funnel while maintaining the reaction temperature at -20°-25°C. The reaction is usually done when the DIBAL add is completed. If... 

H-benzopyran core structure. This approach for the construction of the 2H-benzopyran scaffold was developed by Shigemasa [22]. However, the authors found that the reaction of the ethyl ester with the aldehyde was extremely slow under Shigemasa s conditions. 

Jeanneret, V. et al. Carbaxylosides of 4-Elhyl-2-oxo-2H-benzopyran-7-yl as Non-Hydrolizable, Orally Active Venous Antithrombotic Agents. 3.1 1998 [129]... 

As mentioned earlier, 2H-1 -benzopyrans are often referred to, especially in the older literature, by the common name chromenes. The more proper term 2H-1-benzopyran is used in this chapter even though many of the references cited in this (and earlier) sections have used the chromene terminology. The structure and numbering system for 2H- -benzopyrans is shown in Figure 3.17. 

Figure 3.19. Representative examples of 2H- -benzopyrans annellated with heteroaromatic groups on the f-face.

In the reaction of isatins with some cyclic ketones, such as 4-hydroxy-2H-benzopyran-2-one, the initial dioxindole formed reacts with a second equivalent of the ketone yielding a 3,3-disubstituted oxindole. 

Estrogen antagonists consisting of 4-fluoroalkyl-2H-benzopyrans, (IV), and 3,4-dihydroquinoline derivatives were prepared by Kuenzer (5) and Wallace (6), respectively, for use as antiuterus growth agents. 

DIETHYL-0-(3-CHL0R0-4-METHYL-2-0X0-2H-BENZOPYRAN-7-YL)PHOSPHOROTHIOATE see CNU750... 

When rare-earth-metal ions such as Eu and Tb are bound to polyelectrolyte membranes such as poly(sodium acrylate) and poly(sodium ethene-sulphonate) their fluorescence intensities are considerably enhanced this is associated with the formation of asymmetric bonds between the rare-earth ions and the acrylate/S03 groups in the polymers. This was confirmed by the addition of EDTA to the Tb -poly(sodium acrylate) complex which, because of its preferential binding to the polymer, displaced Tb ions and resulted in reduced fluorescence of the latter. Stokes shifts of fluorescent dyes in different polymer systems have been related more to mobility effects in the polymer than polarity,and the fluorescence of hydrolysed aspirin has been found to be affected by the nature of different polymer supports.The luminescence properties of cis-(2,2 -bipyridyl)ruthenium(ii) complexes have been found to be influenced by binding the complex to a polymer matrix,as have the luminescence properties of flavones and l-octadecyl-3,3-dimethyl-6 -nitrospiro(indoline-2,2 -2H-benzopyran). Other studies of interest in-... 

Coumarins are natural compounds that contain characteristic benzo[a]pyrone (2H-benzopyran-2-one) moiety. They are especially abundant in UmbelUferae, Rutaceae, Leguminosae, and other plant families. Different coumarin derivatives have been isolated. Usually the substituents are at the positions C5, Cg, C7, and Cs [e.g., umbelliferone (7-hydroxycoumarin), hier-niarin (7-methoxycoumarin), esculetin (6,7-dihydrox-ycoumarin), scopoletin (6-methoxy-7-hydroxy-coumarin), osthenol (7-hydroxy-8-prenylcoumarin), osthol (7-methoxy-8-prenylcoumarin), and others]. 

The other angular pyrazoloquinoline derivative 327 was obtained by hydrazinolysis of 2-imino-7,7-dimethy-4-methylsulfanyl-5-oxo-5,6,7,8-tetrahydro-2H-benzopyran-3-carbonitrile (326). The reaction can be proceeded by substitution of the methylsulfanyl group by hydrazine followed by cyclization to give 327 (97JCR(S)256) (Scheme 61). 

A synthesis of benzopyrans 429 was performed by condensation of disubstituted a,[l-unsatura ted aldehydes 427 with 1 (75TL3407) the firstly formed dienones 428 underwent valence isomerization to give the stable 2H-benzopyrans 429. When the reaction was carried out at room temperature in pyridine, a small amount of 428 was isolated together with the major product 429 (75TL3407). When the monosubstituted... 

The 2-phenyl analogue of this compound, 6-acetyl-7,8-di hydroxy-2-phenyl-3,4-dihydro-2H-benzopyran has been prepared in 35% yield by the gradual addition over 6 hours of cinnamyl alcohol in benzene solution to a stirred suspension at 60°C of 2,3,4-trihydroxyacetophenone in orthophosphoric acid in benzene (2 5) with continuance of reaction for a further 12 hours. Some uncyclised material, 5-cinnamyl-2,3,4-trihydroxyacetophenone (25%) was cyclised by heating with phosphoric acid at 80°C at which temperature the starting material furnished only the cyclised product directly in 55% yield (ref. 14). 

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