Platinum-Catalyzed Direct Amination of Allylic Alcohols under Mild Conditions: Ligand and Microwave Effects, Substrate Scope, and Mechanistic Study
Platinum-Catalyzed Direct Amination of Allylic Alcohols under Mild Conditions: Ligand and Microwave Effects, Substrate Scope, and Mechanistic Study
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DOI：
10.1021/ja9046075
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发表时间：
2009-10-14
影响因子：
15
通讯作者：
Mashima, Kazushi
中科院分区：
文献类型：
--
作者：
Ohshima, Takashi;Miyamoto, Yoshiki;Mashima, Kazushi
过渡金属催化烯丙基化合物经-烯丙基金属中间体胺化反应是合成烯丙胺的一种有效方法。烯丙醇直接催化取代的唯一副产物是水，近年来因其环境和经济上的优势而受到人们的关注。在这里，我们描述了一种使用Pt-Xantphos和Pt-DPEphos催化剂系统的芳基和烷基取代烯丙醇与各种胺的通用直接催化胺化的发展，它允许选择性合成各种单烯丙胺，如生物活性化合物Naftifine和Flunarizine，在不需要活化剂的情况下收率高。配体的选择是获得高催化活性的关键，我们证明，不仅大的咬角，而且连接氧原子的Xantphos和DPEphos配体是非常重要的。此外，与常规加热相比，微波加热对催化剂活性有显著影响，并显著缩短了反应时间。此外，一些机制研究，包括H-1和P-31{H-1} NMR研究；Pt(xantphos)Cl-2、Pt(eta(2)-C3H5OH)（xantphos）等催化中间体的分离与表征；用x射线晶体学分析证实了[Pt（eta(3)-烯丙基）（xantphos）]OTf的结构交叉实验表明，通过消除水形成pi-烯丙基铂配合物是一个不可逆的速率决定步骤，催化循环中的其他过程是可逆的，即使在室温下也是可逆的。
Transition metal-catalyzed amination of allylic compounds via a pi-allylmetal intermediate is a powerful and useful method for synthesizing allylamines. Direct catalytic substitution of allylic alcohols, which forms water as the sole coproduct, has recently attracted attention for its environmental and economical advantages. Here, we describe the development of a versatile direct catalytic amination of both aryl- and alkyl-substituted allylic alcohols with various amines using Pt-Xantphos and Pt-DPEphos catalyst systems, which allows for the selective synthesis of various monoallylamines, such as the biologically active compounds Naftifine and Flunarizine, in good to high yield without need for an activator. The choice of the ligand was crucial toward achieving high catalytic activity, and we demonstrated that not only the large bite-angle but also the linker oxygen atom of the Xantphos and DPEphos ligands was highly important. In addition, microwave heating dramatically affected the catalyst activity and considerably decreased the reaction time compared with conventional heating. Furthermore, several mechanistic investigations, including H-1 and P-31{H-1} NMR studies; isolation and characterization of several catalytic intermediates, Pt(xantphos)Cl-2, pt(eta(2)-C3H5OH)(xantphos), etc; confirmation of the structure of [Pt(eta(3)-allyl)(xantphos)]OTf by X-ray crystallographic analysis; and crossover experiments, suggested that formation of the pi-allylplatinum complex through the elimination of water is an irreversible rate-determining step and that the other processes in the catalytic cycle are reversible, even at room temperature.