Modified chromones

In an unusual modified chromone synthesis, enaminones formally derived from o-hydroxyacetophenone react with selenium oxychloride prior to cyclisation resulting in the formation of Se-bridged bischromones. Various reactions at Se are described, including fission of an Se-Se bond, leading to chromone-3-seleninic acid (95JHC43). 

Modified chromones 138 have been synthesized according to the sequence depicted in Scheme 32. The 4-substituted 2-hydroxyacetophe-nones 134 (R = Me 134a, = H 134b) are first O-acylated to produce... 

According to our previous reports [74,76], the anti-inflammatory activity of ethers of 4-bromomethyl coumarins can be significantly modified by using different aryl systems. Here we have modified the aryl moieties to heterocyclic moieties like chromone, benzofuran and coumarin... 

In a different approach dihydrochalcones have been transformed to 3-benzyl-4-chromones. Treatment of (37) with ethyl formate and sodium led to (38) which on hydrogenation and selective demethylation yielded racemic 4 -0-methyl-3,9-dihydropunctatin (18) (25). A modified method... 

Reversed-phase HPLC is the method recommended for the screening of plant materiaL in which chromone alkaloids can be present. Mostly C-18 columns were applied with aqueous mobile phases containing high concentrations of buffer at pH 4.5-6.5, modified with methanol or acetonitrile. Polyhydroxy alkaloids of the pyrrohdine, piperidine, pyrro-lizidine, indolizidine, and tropane classes, because of their lack of a suitable chromophore, have rarely been analyzed... 

Gomberg, Cone and Kyriakides [105] modified the method by reacting chlorofumaric acid with hot sodium phenoxide, the excess of phenol having been previously removed under vacuum. In this way, a high yield (97 per cent) of chromone-2-carboxylic acid was obtained. More recently, an improved conversion of a thiophenol to a l-thiochromone-2-carboxylic ester was achieved by Bossert [106] by condensation with 3-oxoesters (/S-keto-esters) under the influence of polyphosphoric acid (PPA). 

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