Efficient Construction of Pyrano[3,2-a]carbazoles: Application to a Biomimetic Total Synthesis of Cyclized Monoterpenoid Pyrano[3,2-a]carbazole Alkaloids
Efficient Construction of Pyrano[3,2-a]carbazoles: Application to a Biomimetic Total Synthesis of Cyclized Monoterpenoid Pyrano[3,2-a]carbazole Alkaloids
复制标题
DOI：
10.1002/chem.201301792
复制
发表时间：
2013-10-11
影响因子：
4.3
通讯作者：
Knoelker, Hans-Joachim
中科院分区：
文献类型：
--
作者：
Hesse, Ronny;Gruner, Konstanze K.;Knoelker, Hans-Joachim
我们已经开发了一种通过钯催化构建咔唑骨架的高效路线来制备2-羟基-3-甲基咔唑（1）。使用1作为中继化合物，已经测试了通过与萜类化合物结构单元反应进行吡喃环成环的不同方法。刘易斯酸促进的1与异戊烯醛（21）的反应开辟了一条合成吉瑞宁宾（3）的有效途径，相应的与柠檬醛（25）的反应得到了马汉宁宾（5）。化合物3和5经氧化得到九里香碱（4）和九里香碱（6）。根据生物遗传学的建议，Mahanimbine（5）已被用于环化单萜吡喃并[3，2-a]咔唑生物碱cyclomahanimbine（7）、Mahanimbidine（8）和bicyclomahanimbine（9）的有效仿生合成。描述了5，7，8和9的相互转化，并讨论了其机理。通过X射线晶体结构测定明确验证结构归属。此外，cyclomahanimbine（7）转化为murrayazolinine（10）和exozoline（11）。
We have developed a highly efficient route to 2-hydroxy-3-methylcarbazole (1) via a palladium-catalyzed construction of the carbazole skeleton. Using 1 as relay compound, different methods for annulations of pyran rings by reaction with terpenoid building blocks have been tested. The Lewis acid promoted reaction of 1 with prenal (21) opened up an efficient route to girinimbine (3) and the corresponding reaction with citral (25) afforded mahanimbine (5). Oxidation of compounds 3 and 5 provided murrayacine (4) and murrayacinine (6). Following the biogenetic proposal, mahanimbine (5) has been exploited for efficient biomimetic syntheses of the cyclized monoterpenoid pyrano[3,2-a]carbazole alkaloids cyclomahanimbine (7), mahanimbidine (8) and bicyclomahanimbine (9). The interconversions of 5, 7, 8 and 9 are described and mechanistic implications are discussed. Structural assignments are unambiguously verified by X-ray crystal structure determinations. Moreover, cyclomahanimbine (7) was transformed into murrayazolinine (10) and exozoline (11).