Studies of the Selective O-Alkylation and Dealkylation of Flavonoids.XX. A Convenient Method for Synthesizing 5,6,7-Trihydroxyisoflavones and 5,6-Dihydroxy-7-methoxyisoflavones.
作者:Tokunaru HORIE、Masahiro SASAGAWA、Fumihito TORII、Yasuhiko KAWAMURA、Kazuyo YAMASHITA
DOI:10.1248/cpb.44.486
日期:——
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-methoxy-isoflavones. 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 isoflanones were examined and some natural isoflavones were identified.
3',6'-双(苄氧基)-2',4'-二甲氧基查尔酮,源自3,6-二羟基-2,4-二甲氧基乙酰苯酮的二苄醚,在甲醇中通过氧化性重排与硝酸铊(III)(TTN)反应,生成2-芳基-1-[3,6-双(苄氧基)-2,4-二甲氧基苯基]-3,3-二甲氧基丙酮;这些产物通过氢解后环化转化为6-羟基-5,7-二甲氧基异黄酮。异黄酮的乙酸酯中的5-甲氧基在乙腈中以5%(质量体积比)无水溴化铝选择性裂解,定量得到相应的5-羟基异黄酮,这些异黄酮再水解为5,6-二羟基-7-甲氧基异黄酮。乙酸酯还通过在70°C下乙腈中30%(质量体积比)无水氯化铝处理36-48小时脱甲基化,得到5,6,7-三羟基异黄酮。对这些异黄酮的光谱特性进行了检验,并鉴定了一些天然异黄酮。