• V B Mahesh

      Articles written in Proceedings – Section A

    • Synthetic experiments in the benzopyrone series - Part XLII. A new synthesis of 5 : 6 : 7-trihydroxy isoflavone derivatives

      V B Mahesh N Narasimhachari T R Seshadri

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      Using the more easily accessible 5:7: 8-trihydroxy derivatives of isoflavones a convenient method has been worked out for the synthesis of 5: 6: 7-trihydroxy derivatives. It consists in the alkali fission of 5-hydroxy-7: 8-dimethoxy isoflavone and its 2-methyl derivative to yield 2: 6-dihydroxy-3: 4-dimethoxy-phenyl-benzyl ketone. This ketone on treatment with ethyl formate and sodium yields 5-hydroxy-6 : 7-dimethoxy isoflavone. Vigorous acetylation of the ketone using acetic anhydride and sodium acetate yields 2-methyl-5-hydroxy-6: 7-dimethoxy isoflavone which is compared with an authentic sample prepared by an independent method. 5-Hydroxy-7 : 8-dimethoxy isoflavone yields a small quantity of 5-hydroxy 6: 7-dimethoxy isoflavone during alkali fission.

    • Stereochemistry of 3-hydroxy flavanones

      V B Mahesh T R Seshadri

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      A number of 3-hydroxy flavanones occur in nature and several have been obtained using a number of synthetic methods. Though they behave generally in the same way when subjected to drastic methods of dehydrogenation or dehydration, those obtained by substitution of flavanones in the 3-position seem to differ markedly from others in their reactions towards mild reagents such as dilute sulphuric acid and iodine. This is attributed to stereo-chemical differences. In this particular synthetic method the 3-hydroxyl is axial (H2O elimination easy) whereas in the others it is equatorial (H2 elimination easy). In flavanones substitution of the axially disposed C-H is the favoured one because it is sterically unhindered.

    • Modifications in the iodine oxidation of hydroxy flavanones and their methyl ethers

      R N Goel V B Mahesh T R Seshadri

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      A modified procedure for the action of iodine and silver acetate gives rise to purer products. Agreeing with earlier observations, hesperetin gives a good yield of 3-acetoxy hesperetin and hesperetin 7∶3′-dimethyl ether yields the 3-iodo-compound. The iodoflavanones invariably yield the corresponding flavones by the action of pyridine. In the treatment with alcoholic potash, those which have a free 5-hydroxyl,e.g., 3-iodo naringenin 7∶4′-dimethyl ether and 3-iodo hesperetin 7∶3′-dimethyl ether yield only the corresponding flavones; whereas 3-iodo-5∶7-dimethoxy flavanone having no free 5-hydroxyl group gives a mixture of products, containing the flavone, the flavonol and the 2-hydroxy-2-benzyl 4∶6-dimethoxy coumaranone. The difference seems to depend on the stability of the oxygen ring.

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