Ketones khellin

The oxidation of the cyclic enol ether 93 in MeOH affords the methyl ester 95 by hydrolysis of the ketene acetal 94 formed initially by regioselective attack of the methoxy group at the anomeric carbon, rather than the a-alkoxy ketone[35]. Similarly, the double bond of the furan part in khellin (96) is converted ino the ester 98 via the ketene acetal 97[l23],... 

Many substituted benzofurans show marked pharmacological activity. 2-(4-Hydroxyben-zoyl)benzofuran exhibits a relaxant effect on histamine and acetylcholine spasm. 2-Ethyl-3 -(4-hydroxy-3,5-diiodobenzyl)benzofuran has been shown to be superior to khellin as a coronary dilator. 2-Butyl-3-benzoylfuranyl 4-diethylaminoethoxy-3,5-diiodophenyl ketone, an anginal drug which causes coronary dilation, depresses myocardial oxygen consumption (74HC(29)l). 

The ring closure of orf/io-substituted phenols is a route to production of benzo[6]furans on an industrial scale. The natural benzo[6 ]furan derivatives karanjin, pongapin, khellin and visnagin have been prepared via the respective o-hydroxyarylacetaldehydes, whilst an extension to the cyclization of o-hydroxybenzyl alkyl ketones has made it possible to synthesize polycyclic benzo[6]furans under the influence of demethylating and dehydrating media. Pterocarpans have been synthesized from suitable isoflavones by this route. 

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