Stereoselective Total Synthesis of Natural (+)-Streptazolin via a Palladium-Catalyzed Enyne Bicyclization Approach
作者:Hironari Yamada、Sakae Aoyagi、Chihiro Kibayashi
DOI:10.1021/ja9529910
日期:1996.1.1
The natural Z isomer of (+)-streptazolin (1), isolated from cultures of Streptomyces viridochromogenes, was synthesized in an optically pure form for the first time on the basis of a palladium-catalyzed enyne bicyclization approach in 12 steps and 4.3% overall yield from (3R,4R)-3,4-bis(benzyloxy)succinimide (5). The requisite enyne 13 for palladium-catalyzed bicyclization was prepared from 5 via N-acyliminium
(+)-链霉唑啉 (1) 的天然 Z 异构体,从 Streptomyces viridochromogenes 的培养物中分离出来,在钯催化的烯炔双环化方法的基础上,首次以光学纯的形式合成,分 12 步,总产率为 4.3% (3R,4R)-3,4-双(苄氧基)琥珀酰亚胺(5)的产率。钯催化双环化所需的烯炔 13 由 5 通过乙酰氧基内酰胺 9 的 N-酰基胺离子环化、用 DIBALH-BuLi 部分还原 10 和转化为二溴烯烃 12 制备。 钯催化的最佳结果当用 30 mol% Pd(OAc)2 和 N,N'-双(亚苄基)乙二胺 (BBEDA) 作为配体在苯中回流处理时获得双环化,从而提供 1,2,4a 的 93:7 混合物,7a,6, 7-六氢-5H-1-吡啶 (Z)-14 及其异构化产物 (Z)-15,总产率为 84%。(Z)-14 中的 1,4-二烯异构化为 1,3-二烯是通过用十二羰基三铁处理生成稳定的三碳