Heating of cycloalkanone-2-carboxylate with β-arylethylamine, and oxalylation of the resulting enamino-ester followed by Lewis acid-catalyzed intramolecular cyclization afforded various erythrinan-type heterocycles in excellent yields. This method is widely applicable not only to the synthesis of erythrinans but also to that of A-nor and A-homo analogs and ring-D variants of erythrinan. The alkoxycarbonyl group on the products was readily removed by a new decarbalkoxylation method (heating with magnesium chloride-dimethyl sulfoxide combination). Thus, starting from 2-ethoxycarbonyl-4, 4-ethylenedioxy-cyclohexanone, the 2, 8-dioxo-erythrinan derivative (35) was synthesized in several steps in high yield, and was readily converted to the natural Erythrina alkaloid, 3-demethoxyerythratidinone.
将环烷酮-2-
羧酸酯与β-芳基
乙胺加热,并对所得到的烯胺酯进行草酰化,随后经过
路易斯酸催化的分子内环化反应,可以很好地获得多种红豆杉类
杂环化合物。该方法不仅广泛适用于红豆杉类化合物的合成,还可用于A-去甲基和A-同源物以及红豆杉的环-D变体的合成。产品中的烷氧羰基团可以通过一种新的去羧基化方法(与
氯化镁-二甲基亚
硫酰胺的组合加热)轻松去除。因此,从2-乙氧羰基-4,4-
乙烯基二氧
环己酮出发,经过几步反应以高产率合成了2,8-二氧红豆杉派
生物(35),并可以很容易地转化为天然红豆杉
生物碱3-去
甲氧基红豆杉啶酮。