Chemical and Pharmaceutical Bulletin p. 486 - 491 (1996)
Update date:2022-08-02
Topics: Synthesizing Flavonoids Experimental Studies O-Alkylation Dealkylation Convenient method 5,6,7-trihydroxyisoflavones 5,6-dihydroxy-7-methoxyisoflavones
Horie, Tokunaru
Sasagawa, Masahiro
Torii, Furaihito
Kawamura, Yasuhiko
Yamashita, Kazuyo
3′,6′-Bis(benzyloxy)-2′,4′-dimethoxychalcones, which were derived from dibenzyl ether of 3,6-dihydroxy-2,4-dimethoxyacetophenone, were oxidatively rearranged with thallium(III) nitrate (TTN) in methanol to give 2-aryl-1-[3,6-bis(benzyloxy)-2,4-dimethoxyphenyl]-3,3-dimethoxypropan-1-ones; these products were converted into 6-hydroxy-5,7-dimethoxyisoflavones by hydrogenolysis followed by cyclization. The 5-methoxy group in the acetates of the isoflavones was selectively cleaved with 5% (w/v) anhydrous aluminum bromide in acetonitrile to give quantitatively the corresponding 5-hydroxyisoflavones, which were hydrolyzed to 5,6-dihydroxy-7-methoxyisoflavones. The acetates were also demethylated to 5,6,7-trihydroxyisoflavones with 30% (w/v) anhydrous aluminum chloride in acetonitrile at 70 °C for 36-48 h. The spectral properties of these isoflavones were examined and some natural isoflavones were identified.
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