Structural requirements for substrate in highly enantioselective hydrogenation over the cinchonidine-modified Pd/C
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- 作者：Takashi Sugimura ; Takayuki Uchida ; Junya Watanabe ; Takeshi Kubota ; Yasuaki Okamoto ; Tomonori Misaki ; Tadashi Okuyama
- 关键词：Asymmetric heterogeneous catalysis ; Enantioselective hydrogenation ; Palladium on carbon ; Chiral modification ; Olefin ; Molecular recognition
- 刊名：Journal of Catalysis
- 出版年：2009
- 出版时间：15 February 2009
- 年：2009
- 卷：262
- 期：1
- 页码：57-64
- 全文大小：434 K
文摘
Relationship between substrate structure and enantioselectivity is studied for the asymmetric hydrogenation of 42 different (E)-α,β-disubstituted acrylic acids (propenoic acids) over cinchonidine-modified Pd/C. The β-phenyl group is indispensable for high enantioselectivity of α-phenylcinnamic acid (2,3-diphenylpropenoic acid, 81 % ee), and substitution on this group affects markedly the selectivity. The high ee up to 92 % was achieved by the β-p-alkoxyphenyl substitution, and the selectivity is ascribed mainly to stronger interaction of the substrate with the chiral modifier on the catalyst surface. In contrast, substitution on the α-phenyl group does not affect notably the enantioselectivity (80–82 % ee) or even the α-phenyl group itself is not indispensable but replaceable with a properly bulky group for the high enantioselectivity.