Acridone alkaloids pyranoacridones

In terms of organization, biosynthetic considerations take precedence. These are followed by a description of the various groiqrs of naturally occurririg acridone alkaloids the simple aoidones, C-prenylacridones, futoacridones, pyranoacridones, and finally the dimeric acridone all oids and related compounds. 

Tables II, HI, IV and V survey the structures, properties and the distribution of naturally occurring C-prenylacridones, furanoacridones, pyranoacridones and dimeric acridone alkaloids, respectively.

Dihydroxyacridone prepared in this way has been used fiequently as a starting material for e synthesis of other acridone alkaloids including simple O-and JV-alkylated derivatives (288) and more complex C-prenylanidones (289), pyranoacridones (290,291), and acridone-coumarin mers (292). 

The key step of the acridone synthesis introduced by Coppola is the condensation of a A methylisatoic anhydride with the lithium enolate of a 2-cyclohexen-l-one. The formed diketo intermediate spontaneously cyclizes into a dihydroacridone, easily aromatized to the corresponding acridone. The versatility of this method, which enables carbon-carbon and carbon-nitrogen bond formation under very mild conditions, is illustrated by the efficient syntheses of the demethoxy analogues of natural fliro and pyranoacridones 319, 320), as well as by those of several naturally occurring alkaloids, including 10-methylacridone (30),... 

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