Seegerer, Andreas and Hioe, Johnny and Hammer, Michael M. and Morana, Fabio and Fuchs, Patrick J. W. and Gschwind, Ruth M. (2016) Remote-Stereocontrol in Dienamine Catalysis: Z-Dienamine Preferences and Electrophile-Catalyst Interaction Revealed by NMR and Computational Studies. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 138 (31). pp. 9864-9873. ISSN 0002-7863,
Full text not available from this repository. (Request a copy)Abstract
Catalysis with remote-stereocontrol provides special challenges in design and comprehension. One famous example is the dienamine catalysis, for which high ee values are reported despite insufficient shielding of the second double bond. Especially for dienamines with variable Z/E-ratios of the second double bond, no correlations to the ee values are found. Therefore, the structures, thermodynamics, and kinetics of dienamine intermediates in S-N-type reactions are investigated. The NMR studies show that the preferred dienamine conformation provides an effective shielding if large electrophiles are used. Calculations at SCS-MP2/CBS-level of theory and experimental data of the dienamine formation show kinetic preference for the Z-isomer of the second double bond and a slow isomerization toward the thermodynamically preferred E-isomer. Modulations of the rate-determining step, by variation of the concentration of the electrophile, allow the conversion of dienamines to be observed. With electrophiles, a faster reaction of Z- than of E-isomers is observed experimentally. Calculations corroborate these results by correlating ee values of three catalysts with the kinetics of the electrophilic attack and reveal the significance of CH-pi and stacking interactions in the transition states. Thus,, for the first time a comprehensive understanding of the remote stereocontrol in gamma-functionalization reactions of dienamines and an explanation to the "Z/E-dilemma" are presented. The combination of bulky catalyst subsystems and large electrophiles provides a shielding of one face and causes different reactivities of E/Z-dienamines in nucleophilic attacks from the other face. Kinetic preferences for the formation of Z-dienamines and their unfavorable thermodynamics support high ee values.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | PROLINOL ETHER ENAMINES; IMINIUM ION ACTIVATION; ALPHA,BETA-UNSATURATED ALDEHYDES; NONCOVALENT INTERACTIONS; MAGNETIC-RESONANCE; CONJUGATE ADDITION; FORMATION PATHWAY; GAMMA-ALKYLATION; SILYL ETHERS; DIELS-ALDER; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Arbeitskreis Prof. Dr. Ruth Gschwind |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 08 Apr 2019 06:14 |
| Last Modified: | 08 Apr 2019 06:14 |
| URI: | https://pred.uni-regensburg.de/id/eprint/3494 |
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