The total synthesis of the Erythrina alkaloid (±)-3-demethoxyerythratidinone (20) has been accomplished in 39% overall yield from homoveratrylamine(1)by 8 chemical operations, using a tandem cationic cyclization of the Pummerer rearrangement intermediate derived from the sulfoxide 5 as the key step. Of particular interest is the observation that heating of 5 with p-toluenesulfonic acid provides the erythrinan 6 (and the deprotected derivative 7) as a single stereoisomer, whereas similar treatment of 5 in the presence of ethylene glycol gives initially the bicyclic lactam 8, which then cyclizes under the reaction conditions used to afford a mixture of two diastereomeric erythrinans 6 and 9.A possible explanation of these contrasting results is presented.
以从亚砜 5 中得到的普默尔重排中间体的串联阳离子环化为关键步骤,通过 8 次
化学反应,以均
藜芦胺(1)为原料,完成了红景天
生物碱 (±)-3-demethoxyerythratidinone (20) 的全合成,总收率为 39%。特别值得注意的是,用
对甲苯磺酸加热 5,可得到单一立体异构体的
赤藓红 6(以及去保护衍
生物 7),而在
乙二醇存在下对 5 进行类似处理,最初可得到双环内酰胺 8,然后在所用的反应条件下发生环化,得到两种非对映
赤藓红 6 和 9 的混合物。