Synthetic studies on isoquinoline alkaloids. II. Selective conversion of 3,9,10-substituted tetrahydroprotoberberines into 3,9,10-substituted 5,6,7,8,13,14-hexahydrodibenz(c,g)azecines.
作者:WATARU NAGATA、KYO OKADA、HIROSHI ITAZAKI、SHOICHIRO UYEO
DOI:10.1248/cpb.23.2878
日期:——
An efficient method for highly selective conversion of 3, 9, 10-trisubstituted tetrahydroprotoberberines into the corresponding 3, 9, 10-substituted 5, 6, 7, 8, 13, 14-hexahydrodibenz (c, g) azecines was established as exemplified by high yield conversions of 13 into 15 and 1g into 29. The method involves Emde reduction (Birch modification) of the methiodide 14 or 28, in which the C9-phenolic function is specifically protected by the benzyl group enabling selective reductive fission at the C13a-N bond. By application of this method combined with the method newly developed in our laboratory for synthesis of 9, 10-substituted tetrahydroprotoberberines, a straight-forward and sophisticated total synthesis of 9, 10-dimethoxy-3-hydroxy-7-methyl-5, 6, 7, 8, 13, 14-hexahydrodibenz (c, g)-azecine (2a) was achieved as illustrated in Chart 8. The cyclopropylmethyl group was newly introduced as a very useful protecting group for a phenolic function.
建立了一种将 3,9,10-三取代的四氢原小檗碱高度选择性转化为相应的 3,9,10-取代的 5,6,7,8,13,14-六氢二苯(c,g)吖嗪的有效方法,例如13 转化为 15 以及 1g 转化为 29 的高产率转化。该方法涉及甲基碘化物 14 或 28 的 Emde 还原(Birch 改性),其中 C9-酚官能团受到苄基的特异性保护,从而能够在 C13a- N键。应用该方法结合本实验室新开发的9, 10-取代四氢原小檗碱合成方法,简单、精密地全合成了9, 10-二甲氧基-3-羟基-7-甲基-5, 6 , 7, 8, 13, 14-六氢二苯(c, g)-吖嗪(2a)如图8所示。新引入的环丙基甲基作为酚官能团的非常有用的保护基团。