Palladium-catalyzed borylation of aryl chlorides: Scope, applications, and computational studies
Palladium-catalyzed borylation of aryl chlorides: Scope, applications, and computational studies
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DOI：
10.1002/anie.200701551
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发表时间：
2007-01-01
影响因子：
16.6
通讯作者：
Buchwald, Stephen L.
中科院分区：
文献类型：
--
作者：
Billingsley, Kelvin L.;Barder, Timothy E.;Buchwald, Stephen L.
芳基硼酸和芳基硼酸酯是有机合成的通用试剂，可用于制备各种碳-氧、碳-氮和碳-碳键。[1]此外，由于其高稳定性和低毒性，使用有机硼烷进行交叉偶联过程特别有吸引力。然而，硼酸和酯通常是通过中间体烷基和芳基锂化合物或格氏试剂制备的，这些过程与许多官能团不相容。 [2]此外，通常需要使用芳基碘化物或芳基溴化物，而更容易获得的芳基氯化物[3]通常是不合适的前体。近年来，各种过渡金属催化工艺的发展使得可以在更温和的条件下制备芳基硼酸酯。 [4]特别是，已经出现了许多钯催化的方法，用于将芳基碘化物、芳基溴化物和三氟甲磺酸酯转化为相应的频哪醇或儿茶酚硼酸酯。 [5]然而，只有两篇报道[6]将未活化的芳基氯作为合适的偶联伙伴，并且这些方法有几个缺点：1）许多底物需要大量的钯催化剂（5-6 mol%）。 2）需要较长的反应时间（24-48小时）。 3) 表现出有限的底物范围和官能团耐受性（例如，很少或没有邻位取代基、苯酚和苯胺的例子）。在此，我们报道了一种由 Pd 和二烷基膦联苯配体 1 或 2 组成的活性催化剂，可有效地将芳基氯转化为频哪醇硼酸酯，并首次允许从两种芳基氯直接“一锅”合成对称和不对称联芳基化合物。此外，还进行了计算研究，深入了解联芳基单膦配体在钯催化硼化过程中的功效。
Aryl boronic acids and esters are versatile reagents for organic synthesis that are utilized in the preparation of various carbon–oxygen, carbon–nitrogen, and carbon–carbon bonds.[1] In addition, the use of organoboranes for crosscoupling processes is particularly attractive owing to their high stability and low toxicity. However, boronic acids and esters usually are prepared via intermediate alkyl and aryllithium compounds or Grignard reagents, processes that are not compatible with numerous functional groups.[2] Furthermore, the use of aryl iodides or bromides is often necessary, while the more readily available aryl chlorides [3] are often unsuitable precursors. In recent years, the development of a variety of transitionmetal-catalyzed processes has allowed for the preparation of aryl boronate esters under milder conditions.[4] In particular, numerous palladium-catalyzed methods have emerged for the conversion of aryl iodides, bromides, and triflates to the corresponding pinacol or catechol boronate esters.[5] However, only two reports [6] can be found in which unactivated aryl chlorides are suitable coupling partners, and these methods have several disadvantages: 1) High quantities of palladium catalysts (5–6 mol%) are required for many substrates. 2) Long reaction times (24–48 h) are necessary. 3) Limited substrate scope and functional-group tolerance (eg few or no examples with ortho substituents, phenols, and anilines) is exhibited. Herein, we report an active catalyst composed of Pd and dialkylphosphinobiphenyl ligands 1 or 2 that efficiently converts aryl chlorides to pinacol boronate esters and allows, for the first time, the direct “one-pot” synthesis of symmetrical and unsymmetrical biaryl compounds from two aryl chlorides. In addition, computational studies are presented that provide insight into the efficacy of biaryl monophosphine ligands in the palladium-catalyzed borylation process.