Studies of the Selective O-Alkylation and Dealkylation of Flavonoids. XXII. A Convenient Method for Synthesizing 3,5,7-Trihydroxy-6-methoxyflavones.
作者:Tokunaru HORIE、Kenichi SHIBATA、Kazuyo YAMASHITA、Yasuhiko KAWAMURA、Masao TSUKAYAMA
DOI:10.1248/cpb.45.446
日期:——
The demethylation of 3, 4-dioxygenated 6-methoxy-2-isopropoxyacetophenones was studied and it was found that 4-benzyloxy-6-hydroxy-3-methoxy-2-isopropoxyacetophenone was easily obtained from 4-benzyloxy-3, 6-dimethoxy-2-isopropoxyacetophenone by selective demethylation with anhydrous aluminum bromide-sodium iodide in acetonitrile. The acetophenone was converted into 7-benzyloxy-3-hydroxy-6-methoxy-5-isopropoxyflavones by cyclization followed by oxidation with dimethyldioxirane. The isopropoxy group in the flavones was selectively cleaved with anhydrous aluminum chloride via the corresponding tosylates to give 7-benzyloxy-3, 5-dihydroxy-6-methoxyflavones, which were converted into the desired 3, 5, 7-trihydroxy-6-methoxyflavones by hydrogenolysis. The process was suitable as a general method for synthesizing 3, 5, 7-trihydroxy-6-methoxyflavones and five flavones were synthesized. We also examined the 13C-NMR spectra of twelve kinds of 3, 5, 6, 7-tetraoxygenated 4'-methoxyflavones and revised the proposed structure of a natural flavone.
研究了3, 4-二氧化6-甲氧基-2-异丙氧基苯乙酮的脱甲基反应,发现4-苄氧基-6-羟基-3-甲氧基-2-异丙氧基苯乙酮很容易由4-苄氧基-3, 6-二甲氧基得到4-苄氧基-6-羟基-3-甲氧基-2-异丙氧基苯乙酮-2-异丙氧基苯乙酮,用无水溴化铝-碘化钠在乙腈中选择性脱甲基。通过环化然后用二甲基二环氧乙烷氧化将苯乙酮转化为7-苄氧基-3-羟基-6-甲氧基-5-异丙氧基黄酮。用无水氯化铝通过相应的甲苯磺酸盐选择性裂解黄酮中的异丙氧基,得到7-苄氧基-3,5-二羟基-6-甲氧基黄酮,将其转化为所需的3,5,7-三羟基-6-甲氧基黄酮通过氢解作用。该工艺适合作为合成3,5,7-三羟基-6-甲氧基黄酮的通用方法,并合成了5种黄酮。我们还检查了 12 种 3,5,6,7-四氧化 4'-甲氧基黄酮的 13C-NMR 谱,并修改了天然黄酮的提议结构。