Studies of the Selective<i>O</i>-Alkylation and Dealkylation of Flavonoids. XI. A New Convenient Method for Synthesizing 3,5,7-Trihydroxy-8-methoxyflavones from 7-Hydroxy-3,5,8-trimethoxyflavones
作者:Tokunaru Horie、Masao Tsukayama、Yasuhiko Kawamura、Masamichi Seno、Shigeo Yamamoto
DOI:10.1246/bcsj.61.441
日期:1988.2
The 3- or 5-methoxyl group in the ditosylates of 5,7-dihydroxy-3,4′,8-trimethoxy- and 3,7-dihydroxy-4′,5,8-trimethoxyflavones was quantitatively demethylated with anhydrous aluminum bromide in acetonitrile to give the corresponding monohydroxyflavones, which were easily hydrolyzed into 3,5,7-trihydroxy-4′,8-dimethoxyflavone. On the basis of the results, the following convenient method for synthesizing 3,5,7-trihydroxy-8-methoxyflavones from 7-hydroxy-3,5,8-trimethoxyflavones was established. 7-Hydroxy-3,5,8-trimethoxyflavones or their tosylates were demethylated with 5% w/v anhydrous aluminum bromide in acetonitrile to give a mixture of the corresponding 3- and 5-hydroxyflavones. The mixture was tosylated and the resultant mixture was demethylated under the same conditions. The demethylated products were hydrolyzed with anhydrous potassium carbonate in methanol to give the desired 3,5,7-trihydroxy-8-methoxyflavones in high yields.
用无水溴化铝在乙腈中定量脱甲基,得到相应的单羟基黄酮,这些单羟基黄酮很容易水解成 3,5,7-三羟基-4′,8-二甲氧基黄酮。在此基础上,建立了以下从 7-羟基-3,5,8-三甲氧基黄酮合成 3,5,7-三羟基-8-甲氧基黄酮的简便方法。7- 羟基-3,5,8-三甲氧基黄酮或其对甲苯磺酸盐在乙腈中用 5% w/v 无水溴化铝脱甲基,得到相应的 3- 和 5- 羟基黄酮的混合物。在相同条件下,对混合物进行甲苯磺酰化,并对得到的混合物进行脱甲基处理。脱甲基产物在甲醇中用无水碳酸钾进行水解,以高产率得到所需的 3,5,7-三羟基-8-甲氧基黄酮。