Synthesis of<i>dl</i>-Shikonin by Vanadium(II)-Assisted Cross-Coupling and Electrooxidation of Aromatic Nuclei
作者:Sigeru Torii、Kouji Akiyama、Hidetoshi Yamashita、Tsutomu Inokuchi
DOI:10.1246/bcsj.68.2917
日期:1995.10
Vanadium(II)-assisted cross-coupling of 1,4,5,8-tetramethoxynaphthalene-2-carbaldehyde and 3-methyl-2-butenal was employed for introduction of the side chain of dl-shikonin. 2-(1-Hydroxy-4-methyl-3-pentenyl)-1,4,5,8-tetramethoxynaphthalene was prepared by the pinacol coupling and the subsequent palladium-catalyzed hydrogenolysis of the carbon–oxygen bond at the allylic position of the diol carbonate. Electrochemical oxidation of the 2-substituted 1,4,5,8-tetramethoxynaphthalene, followed by reductive acetylation with zinc and the subsequent electrooxidation of the resulting 5,8-diacetoxy-1,4-dimethoxynaphthalene, afforded the corresponding 5,8-diacetoxy-1,4-naphthoquinone, whose alkaline hydrolysis furnished dl-shikonin.
钒(II)辅助的交叉偶联反应被用于将1,4,5,8-四甲氧基萘-2-醛和3-甲基-2-丁烯醛结合,引入dl-石杉烯的侧链。通过皮那考尔偶联和随后的钯催化氢解二醇碳酸酯的碳氧键,在烯丙位制备了2-(1-羟基-4-甲基-3-戊烯基)-1,4,5,8-四甲氧基萘。对2取代的1,4,5,8-四甲氧基萘进行电化学氧化,随后与锌进行还原乙酰化,接着对所生成的5,8-二乙酰氧基-1,4-二甲氧基萘进行电氧化,得到了相应的5,8-二乙酰氧基-1,4-萘醌,经过碱性水解获得dl-石杉烯。