Tran Yang S, Kwon Ohyun
Department of Chemistry and Biochemistry, University of California, Los Angeles 607 Charles E. Young Drive East, Los Angeles, California 90095-1569, USA.
Org Lett. 2005 Sep 15;7(19):4289-91. doi: 10.1021/ol051799s.
[reaction: see text] An application of the phosphine-catalyzed [4 + 2] annulation in the formal synthesis of alstonerine and macroline is reported. A phosphine-catalyzed [4 + 2] reaction between imine 7a and allene 8 formed the D ring of the target indole alkaloids. A subsequent intramolecular Friedel-Crafts acylation provided the C ring of the bridged tetracycle. Deprotection, followed by methylation of the bridged nitrogen, deoxygenation of the C6 ketone, and reduction of the C16 carbethoxy group provided the previously known intermediate 3.
[反应：见正文] 报道了膦催化的[4 + 2]环化反应在阿斯托宁和马钱子碱形式合成中的应用。亚胺7a与丙二烯8之间的膦催化[4 + 2]反应形成了目标吲哚生物碱的D环。随后的分子内傅克酰化反应提供了桥连四环的C环。脱保护，接着对桥连氮进行甲基化、C6酮脱氧以及C16乙氧羰基还原，得到了先前已知的中间体3。
