• Ishwar-Dass

      Articles written in Proceedings – Section A

    • Synthetic experiments in the benzopyrone series - Part XXV. Isomerisation of 5∶7∶8-hydroxy flavanones

      Ishwar-Dass N Narasimhachari T R Seshadri

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      Heating 2-hydroxy-3∶4∶6-trimethoxy-chalkone with hydrobromic acid yields instead of the expected 7-methoxy-5∶8-dihydroxy flavanone, the isomeric 7-methoxy-5∶6-dihydroxy flavanone. The same product is obtained by the partial demethylation of 2-hydroxy-4∶5∶6-trimethoxy chalkone. Attempts to prepare 5∶8-dihydroxy-7-methoxy flavanone by the reduction of the corresponding quinone again resulted in the formation of the isomeric 7-methoxy-5∶6-dihydroxy flavanone. The 5∶8-dihydroxy compound has been obtained by the partial demethylation of 5∶7∶8-trimethoxy flavanone by means of aluminium chloride in nitrobenzene solution.

    • A new effect of hydrogen bond formation - Part V. A note on the behaviour of the 8-hydroxyl group in benzopyrone derivatives

      Ishwar-Dass N Narasimhachari T R Seshadri

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      Past records indicate that an 8-hydroxyl group in a flavone is involved in chelation but it is of a weak nature. 7-Methoxy-8-hydroxy flavanone can be easily obtained by the partial methylation of 7∶8-dihydroxy flavanone or the partial demethylation of 7∶8-dimethoxy flavanone, and can also be directly obtained from gallacetophenone-4-methyl ether. Its preparation and properties indicate the existence of stronger chelation involving the 8-hydroxyl group. Similar experiments have been done on the preparation of 7-methoxy-8-hydroxy chromone and isoflavone. Though the partial demethylation of 7∶8-dimethoxy compounds has been successful, partial methylation of the dihydroxy compounds has not been possible in these cases. The properties of the products also indicate weaker chelation in the chromone and isoflavone just as in the corresponding flavone. In the course of the synthesis of 7-methoxy-8-hydroxy flavanone and chromone independently for purpose of comparison the preparation of the intermediate gallacetophenone 4-methyl ether has been re-investigated and a convenient method has been worked out.

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