Stereoselective synthesis of 2-dienyl-substituted piperidines using an η4-dienetricarbonyliron complex as the stereocontrolling element in a double reductive amination cascade
作者:Iwan Williams、Keith Reeves、Benson M. Kariuki、Liam R. Cox
DOI:10.1039/b710898b
日期:——
In the presence of NaBH(OAc)3, a 1,5-keto-aldehyde, contained within a side-chain of an η4-dienetricarbonyliron complex, undergoes a double reductive amination sequence with a series of primary amines, to provide the corresponding piperidine products in good to excellent yield. The dienetricarbonyliron complex functions as a powerful chiral auxiliary in this cascade process, exerting complete control over the stereoselectivity of the reaction, with the formation of a single diastereoisomeric product. The sense of stereoinduction has been confirmed by X-ray crystallography. Removal of the tricarbonyliron moiety can be effected with CuCl2 to afford the corresponding 2-dienyl-substituted piperidine in excellent yield. Attempted extension of this cyclisation strategy to the corresponding azepane ring system using a 1,6-keto-aldehyde as the cyclisation precursor was unsuccessful; in this case, the reaction stopped after a single reductive amination on the aldehyde to provide an acyclic keto-amine product.
在 NaBH(OAc)3 的存在下,δ-4-二羰基铁络合物侧链中的 1,5-酮醛会与一系列伯胺发生双还原胺化反应,从而以良好甚至极高的收率得到相应的哌啶产物。在这一级联反应过程中,二羰基铁络合物起着强大的手性辅助作用,可以完全控制反应的立体选择性,形成单一的非对映异构产物。X 射线晶体学证实了立体诱导的意义。用 CuCl2 可以去除三羰基铁分子,得到相应的 2-二烯基取代的哌啶,收率极高。使用 1,6-酮醛作为环化前体,尝试将这种环化策略扩展到相应的氮杂环庚烷环系统,但没有成功;在这种情况下,反应在醛上进行一次还原胺化后就停止了,生成了无环酮胺产物。