Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones,Angewandte Chemie International Edition

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Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones
Angewandte Chemie International Edition ( IF 16.1 ) Pub Date : 2020-11-19 , DOI: 10.1002/anie.202012796
Marvin Titze ₁ , Juliane Heitkämper ₂ , Thorsten Junge ₁ , Johannes Kästner ₂ , René Peters ₁

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Enantiopure secondary alcohols are fundamental high‐value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5–3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an S_N2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.

中文翻译：

用于酮对映选择性硼氢化反应的高活性路易斯酸-铵盐协同催化剂

对映体纯仲醇是基本的高价值合成结构单元。获得此类化合物最有吸引力的方法之一是催化硼氢化反应。我们描述了这种反应类型的一个新概念，该概念允许特殊的催化周转数（高达 15 400），与之前报道的最活跃的催化剂相比，该周转数增加了约 1.5-3 个数量级。在我们的概念中，非质子卤化铵部分与同一催化剂分子内的亲氧性路易斯酸合作。对照实验表明，两个催化中心对于观察到的活性都是必不可少的。动力学、光谱和计算研究表明，氢化物转移是速率限制的，并通过协调机制进行，其中硼上的氢化物不断被碘化物取代，让人想起 S _N 2 反应。该催化剂可以通过几个步骤获得高产率，并且在催化过程中很稳定，易于回收，并且可以重复使用 10 次仍然有效工作。

更新日期：2020-11-19

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