Synthesis and cyclization to aurones and flavones of alkoxy-substituted aryl arylalkynyl ketones

Abstract

Acylation of 1,3,5-tribenzyloxybenzene with alkoxy-substituted phenylpropioloyl chlorides provides the corresponding aryl alkoxylarylalkynyl ketones in which one of the benzyl groups has been removed. Cyclization of these phenolic ketones using basic reagents (potassium carbonate in acetone is best) provides the corresponding aurone system. When the phenolic group of the alkynyl ketones is protected as the t-butyldimethylsilyl ether followed by cyclization, using 18-crown-6 and potassium fluoride, mixtures of the corresponding aurones and flavones are produced. A by-product from the formation of the ketones is the corresponding β-chlorochalcone, which can also be cyclized to an aurone product using basic conditions. Similarly, the t-butyldimethylsilyl ethers of the HCl adducts can also be cyclized to a mixture of the corresponding aurones and flavones.