Pd/C(en) catalyzed chemoselective hydrogenation in the presence of aryl nitriles
Pd/C(en) catalyzed chemoselective hydrogenation in the presence of aryl nitriles
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DOI：
10.1248/cpb.55.837
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发表时间：
2007-05-01
影响因子：
1.7
通讯作者：
Sajiki, Hironao
中科院分区：
文献类型：
--
作者：
Maegawa, Tomohiro;Fujita, Yuki;Sajiki, Hironao
芳香腈不仅是天然产物、药物、除草剂和农药的重要组成部分，而且是各种功能的合成等价物。芳香腈的合成方法的发展在其用途方面一直在增加。由于芳香腈对氢化反应敏感，因此需要开发保留腈基的化学选择性氢化方法。Pd/C是最常用的加氢催化剂之一，许多可还原的官能团如重键、苄基醚、N-Cbz、硝基等在此条件下容易被还原。因此，很难实现含有两个或更多个可还原官能团的底物的化学选择性氢化。我们发现Pd/C催化剂与作为催化毒物的乙二胺（en）形成可分离的络合物[Pd/C（en）]，该络合物催化O-苄基、N-Cbz和O-TBDMS保护基、苯甲醇和环氧化物的多种可还原官能团的化学选择性氢化。在这些研究的过程中，我们发现芳基腈可以在Pd/C（en）催化的氢化条件下在THF中存活，其选择对于有效抑制是重要的。该方法可应用于芳腈存在下烯烃和炔官能团的选择性加氢。
Aromatic nitriles are not only important components of natural products, pharmaceuticals, herbicides and agrochemicals but also a synthetic equivalent of various functionalities. The development of synthetic methods of aromatic nitriles have been increasing in terms of its usefulness. Since aromatic nitriles are susceptible to the hydrogenation, it has been desired for the development of chemoselective hydrogenation method with retention of nitrile groups. Pd/C is one of the most popular catalysts for hydrogenation and many of reducible functional groups such as multiple bonds, benzyl ethers, N-Cbzs, nitro groups and so on could be easily reduced under the conditions. Therefore, it is very difficult to achieve the chemoselective hydrogenation of substrates containing two or more reducible functional groups. We have found that a Pd/C catalyst formed an isolable complex with ethylenediamine (en) employed as catalytic poison, and the complex [Pd/C(en)] catalyzed chemoselective hydrogenation of a variety of reducible functionalities distinguishing O-benzyl, N-Cbz and O-TBDMS protective groups, benzyl alcohols and epoxides. In the course of these investigations, we found the aryl nitriles could survive under the Pd/C(en)-catalyzed hydrogenation conditions in THF whose choice is important for the effective suppression. This methodology could be applied to the selective hydrogenation of alkene and alkyne functionalities in the presence of aromatic nitrile.