Theoretical investigations of Rh-catalyzed asymmetric 1,4-addition to enones using planar-chiral phosphine-olefin ligands |
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Authors: | Kyohei Kawashima Takehiro Sato Masamichi Ogasawara Ken Kamikawa Seiji Mori |
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Institution: | 1. Institute of Quantum Beam Science, Graduate School of Science and Engineering, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512, Japan;2. Department of Natural Science, Graduate School of Science and Technology, Tokushima University, 2-1 Minamijousanjimachicho, Tokushima, Tokushima, 770-8506 Japan;3. Department of Chemistry, Graduate School of Science, Osaka Prefecture University, 1-1 Nakakugakuentyo, Sakai, Osaka 599-8531, Japan |
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Abstract: | Recently, planar-chiral phosphine-olefin ligands based on (η6-arene)chromium(0) and (η5-cyclopentadienyl)manganese(I), which are known as first- and second-generation, respectively, have been developed. These ligands were employed for Rh-catalyzed asymmetric 1,4-addition to enones. First-generation ligands involve high enantioselectivity for cyclic enones (>98% ee). Second-generation ligands involve high enantioselectivity for not only cyclic enones but also for acyclic enones (>98% ee). In this study, we have performed DFT calculations to investigate the origin of enantioselectivity. The theoretical values of enantioselectivities were found to be in good agreement with the experimental values obtained for a cyclic enone, 2-cyclopenten-1-one, using both the first- and second-generation ligands. Regarding an acyclic enone, 3-penten-2-one, it was found that the s-cis type decreases the enantioselectivity because the transition states in the s-cis type have a large steric repulsion. Energy decomposition analysis (EDA) and natural bond orbital (NBO) analysis indicate that it is important to study the orbital interactions in the transition states of the insertion step for the acyclic enone attacked from si-face with the second-generation ligand. © 2018 Wiley Periodicals, Inc. |
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Keywords: | asymmetric conjugate addition olefin-phosphine ligand energy decomposition analysis natural bond orbital analysis steric repulsion nonclassical sp3 C-H…O interaction |
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