The Mechanism of the Rhodium(I)-Catalyzed [2 + 2 + 1] Carbocyclization Reaction of Dienes and CO: A Computational Study
The rhodium(I) catalyzed [2 + 2 + 1] carbocyclization of tethered diene-enes to afford substituted hexahydropentalenones with high levels of diastereoselectivity was modeled using density functional theory. Previously, this transformation was observed to be facile, whereas the analogous bis-ene subs...
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Published in | Journal of the American Chemical Society Vol. 130; no. 17; pp. 5821 - 5830 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
United States
American Chemical Society
30.04.2008
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Subjects | |
Online Access | Get full text |
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Summary: | The rhodium(I) catalyzed [2 + 2 + 1] carbocyclization of tethered diene-enes to afford substituted hexahydropentalenones with high levels of diastereoselectivity was modeled using density functional theory. Previously, this transformation was observed to be facile, whereas the analogous bis-ene substrate could not be cyclized under any reasonable conditions. To establish a conceptual understanding of the carbocyclization mechanism and to identify the functional role of the diene fragment we analyzed the simulated reaction mechanisms using the two parent systems. We discovered a thus far unrecognized, but intuitively plausible, role of the CO ligand for controlling the electron density at the metal center, which affects the feasibility of oxidative addition and reductive elimination steps that are key components of the mechanism. Our calculations suggest that the diene moiety is unique and required because of its ability to undergo a η2→ η4 reorganization allowing for the thermoneutral expulsion of one CO ligand, which in turn generates an electron-rich, coordinatively saturated Rh(I) center that can efficiently promote the oxidative addition with a low barrier. A number of functionalization strategies were considered explicitly to derive a rational plan for optimizing the catalysis and to expose the roles of the different components of the reactant−catalyst complex. |
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Bibliography: | ark:/67375/TPS-NT7J01SG-8 istex:39D2317F683758FC9EE43F5D20F24BE3A998BEFB Cartesian coordinates of computed structures, energies, vibrational frequencies, and additional discussion. This material is available free of charge via the Internet at http://pubs.acs.org. ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 0002-7863 1520-5126 |
DOI: | 10.1021/ja800856p |