Schmid, Markus B. and Zeitler, Kirsten and Gschwind, Ruth M. (2011) NMR Investigations on the Proline-Catalyzed Aldehyde Self-Condensation: Mannich Mechanism, Dienamine Detection, and Erosion of the Aldol Addition Selectivity. JOURNAL OF ORGANIC CHEMISTRY, 76 (9). pp. 3005-3015. ISSN 0022-3263,
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The proline-catalyzed self-condensation of aliphatic aldehydes in DMSO with varying amounts of catalyst was studied by in situ NMR spectroscopy. The reaction profiles and intermediates observed as well as deuteration studies reveal that the proline-catalyzed aldol addition and condensation are competing, but not consecutive, reaction pathways. In addition, the rate-determining step of the condensation is suggested to be the C-C bond formation. Our findings indicate the involvement of two catalyst molecules in the C-C bond formation of the aldol condensation, presumably by the activation of both the aldol acceptor and donor in a Mannich-type pathway. This mechanism is shown to be operative also in the oligomerization of acetaldehyde with high proline amounts, for which the first in situ detection of a proline-derived dienamine was accomplished. In addition, the diastereoselectivity of the aldol addition is evidenced to be time-dependent since it is undermined by the retro-aldolization and the competing irreversible aldol condensation; here NMR reaction profiles can be used as a tool for reaction optimization.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | ALPHA,BETA-UNSATURATED ALDEHYDES; ASYMMETRIC-SYNTHESIS; TRANSITION-STATES; ENAMINE CATALYSIS; ACETALDEHYDE; STEP; STEREOSELECTIVITY; AMINOCATALYSIS; OXAZOLIDINONES; DIARYLPROLINOL; |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie > Arbeitskreis Prof. Dr. Ruth Gschwind Chemistry and Pharmacy > Institut für Organische Chemie > Alumni or Retired Professors > Arbeitskreis Dr. Kirsten Zeitler |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 22 Jun 2020 05:31 |
| Last Modified: | 22 Jun 2020 05:31 |
| URI: | https://pred.uni-regensburg.de/id/eprint/20836 |
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