From Serendipity to Rational Design: Heteroleptic Dirhodium Amidate Complexes for Diastereodivergent Asymmetric Cyclopropanation.
From Serendipity to Rational Design: Heteroleptic Dirhodium Amidate Complexes for Diastereodivergent Asymmetric Cyclopropanation.
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DOI：
10.1021/jacs.2c02258
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发表时间：
2022-04-27
影响因子：
15
通讯作者：
Fuerstner, Alois
中科院分区：
文献类型：
--
作者：
Calo, Fabio Pasquale;Zimmer, Anne;Bistoni, Giovanni;Fuerstner, Alois
最近发现，由三个手性羧酸盐配体和一个非手性乙酰氨基酸酯配体组成的异构性分子桨轮络合物在催化α锡化(硅化和胚化)α-重氮乙酸酯衍生物的不对称环丙烷化反应中是唯一有效的。大量对照实验与详细的计算研究相结合，提供了令人信服的证据，证明了酰胺类化合物的−NH基团与活性Rh卡宾中间体的酯基之间的配体间氢键在立体决定过渡态中起着典型的作用。扭曲这种数组的惩罚超过了立体论，并使四种可能的转变状态中的两种变得不可行。基于这一机理认识，本文重新讨论了母体催化剂的设计：放置适当的外围取代基允许对环丙烷化施加高水平的非对映控制，而原始催化剂缺乏这一点。由于新的配合物允许反式或顺式配置的锡基环丙烷选择性地合成，并且具有极好的光学纯度，这种转化也标志着一种罕见的非对映发散不对称催化。这些产物可以与芳基卤化物或三氟代烯基化合物进行立体定向交叉偶联；这些转化似乎是通过Stille反应形成立体生成的季碳中心的第一个例子；还实现了羰基化偶联。此外，锡/锂交换提供了手性的锂烯烃类化合物，可以被各种亲电伙伴截留。这一新方法的优点和固有的灵活性通过高效合成两种盐内酰胺类化合物来说明，这两种极其稀缺的细菌代谢物具有信号功能，参与生产菌株的自我调节生长抑制。
A heteroleptic dirhodium paddlewheel complex comprising three chiral carboxylate ligands and one achiral acetamidate ligand has recently been found to be uniquely effective in catalyzing the asymmetric cyclopropanation of olefins with α-stannylated (silylated and germylated) α-diazoacetate derivatives. A number of control experiments in combination with detailed computational studies provide compelling evidence that an interligand hydrogen bond between the −NH group of the amidate and the ester carbonyl group of the reactive rhodium carbene intermediate plays a quintessential role in the stereodetermining transition state. The penalty for distorting this array outweighs steric arguments and renders two of the four conceivable transitions states unviable. Based on this mechanistic insight, the design of the parent catalyst is revisited herein: placement of appropriate peripheral substituents allows high levels of diastereocontrol to be imposed upon cyclopropanation, which the original catalyst lacks. Because the new complexes allow either trans- or cis-configured stannylated cyclopropanes to be made selectively and in excellent optical purity, this transformation also marks a rare case of diastereodivergent asymmetric catalysis. The products are amenable to stereospecific cross coupling with aryl halides or alkenyl triflates; these transformations appear to be the first examples of the formation of stereogenic quaternary carbon centers by the Stille reaction; carbonylative coupling is also achieved. Moreover, tin/lithium exchange affords chiral lithium enolates, which can be intercepted with a variety of electrophilic partners. The virtues and inherent flexibility of this new methodology are illustrated by an efficient synthesis of two salinilactones, extremely scarce bacterial metabolites with signaling function involved in the self-regulatory growth inhibition of the producing strain.
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