Synthesis of erythrina and related alkaloids. XXII. Intramolecular cyclization approach. 1): New synthetic route to erythrinan and related heterocycles and synthesis of (.+-.)-3-demethoxy-erythratidinone.
作者:Yoshisuke TSUDA、Yuki SAKAI、Akira NAKAI、Mari KANEKO、Yukie ISHIGURO、Kimiaki ISOBE、Jun-ichi TAGA、Takehiro SANO
DOI:10.1248/cpb.38.1462
日期:——
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。