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Synthesis

C&EN 中文版

双金属催化剂构成5元碳环

并排镍原子催化4+1环加成，为经典的Diels-Alder反应提供可能的5碳类似物

by Bethany Halford
February 21, 2019 | A version of this story appeared in Volume 97, Issue 8
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用六碳骨架制作环或碳环是合成有机化学家的基本练习。问及制作方法，化学家一定会提到忠实可靠的Diels-Alder反应——它通过一个优雅的4+2环加成，结合一个1,3-二烯和一个亲二烯体。此前一直没有相应的制造五碳环的方法，而现在新研究成果出现了突破。普度大学的化学家Christopher Uyeda和You-Yun Zhou公布了一种新的4+1环加成反应，通过1,3-二烯和高反应性亚乙烯基构建环戊烯。

A catalyst with two side-by-side nickel atoms.

Uyeda表示：“这种反应通过非常快捷实用的方式获得五元环。这在环加成化学中一直以来都具有挑战性。”

该反应的关键组分是二镍催化剂，其中两个金属原子并排列置。该催化剂帮助1,1-二氯烯烃形成反应性亚乙烯基，然后引导亚乙烯基与1,3-二烯反应（Science 2019, DOI: 10.1126/science.aau0364）。

Uyeda的团队花了数年时间设计能够支持两个近距离金属原子的配体。他们先是使用二镍催化剂通过烯烃和亚乙烯基之间的2+1环加成制备三碳环，形成亚甲基环丙烷。当Uyeda和Zhou尝试使用1,3-二烯而不是烯烃时，形成了一个五碳环。令人惊讶的是，他们在使用1,3-二烯时从未观察到三碳环产品，这可能是因为相比亚甲基环丙烷，环戊烯更容易生成 。

强有力的证据表明4+1环加成通过逐步机制发生，其中两个新的CC键在不同的步骤中形成。相反，Diels-Alder反应同时形成两个新的CC键。这些不同的机制赋予两种反应不同的优缺点。Uyeda说，与Diels-Alder反应相比，控制4+1环加成反应中的立体化学更为困难。但是这种新反应对一些在Diels-Alder反应中表现不佳的二烯相当有效。

Uyeda说，开发用于4+1环加成的特定催化剂是该研究中最具挑战性的部分。尽管Uyeda和Zhou努力优化反应条件，但第一催化剂的产率从未超过50％。Uyeda说，后来发现将金属配体稍稍增大体积 - 将异丙基换为环戊基，可以显著改善反应，从而产生了突破。Uyeda认为增出的体积可以保护反应性亚乙烯基并防止其分解。

匹兹堡大学开发有机反应的化学家 Kay M. Brummond 说，新的4+1环加成反应“提供了一种令人兴奋的新方法来合成多取代的的环戊烯 。”她表示，因为该反应的前体易于获得，且该反应能耐受多种官能团，包括环氧化物、酯和腈，这对于合成复杂分子会很有用。

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“五元和六元碳环是众多生物学和治疗相关分子的基础，”舍布鲁克大学专攻有机合成的Claude Spino 补充说 。“这些对4+1环加成方法系列的补充令我相信，在不久的未来我们会开发出制造五元碳环的新方法，就像Diels-Alder反应对于制造六元碳环一样强大和普及。”.

本文由Nina Sun为C&EN译为中文。英文原文在此。

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2024 American Chemical Society

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