Gramueller, Johannes and Dullinger, Philipp and Horinek, Dominik and Gschwind, Ruth M. (2022) Bidentate substrate binding in Bronsted acid catalysis: structural space, hydrogen bonding and dimerization. CHEMICAL SCIENCE, 13 (48). pp. 14366-14372. ISSN 2041-6520, 2041-6539
Full text not available from this repository. (Request a copy)Abstract
BINOL derived chiral phosphoric acids (CPAs) are a prominent class of catalysts in the field of asymmetric organocatalysis, capable of transforming a wide selection of substrates with high stereoselectivities. Exploiting the Bronsted acidic and basic dual functionality of CPAs, substrates with both a hydrogen bond acceptor and donor functionality are frequently used as the resulting bidentate binding via two hydrogen bonds is expected to strongly confine the possible structural space and thus yield high stereoselectivities. Despite the huge success of CPAs and the popularity of a bidentate binding motif, experimental insights into their organization and origin of stereoinduction are scarce. Therefore, in this work the structural space and hydrogen bonding of CPAs and N-(ortho-hydroxyaryl) imines (19 CPA/imine combinations) was elucidated by low temperature NMR studies and corroborated by computations. The postulated bidentate binding of catalyst and substrate by two hydrogen bonds was experimentally validated by detection of trans-hydrogen bond scalar couplings. Counterintuitively, the resulting CPA/imine complexes showed a broad potential structural space and a strong preference towards the formation of [CPA/imine](2) dimers. Molecular dynamics simulations showed that in these dimers, the imines form each one hydrogen bond to two CPA molecules, effectively bridging them. By finetuning steric repulsion and noncovalent interactions, rigid and well-defined CPA/imine monomers could be obtained. NOESY studies corroborated by theoretical calculations revealed the structure of that complex, in which the imine is located in between the 3,3 '-substituents of the catalyst and one site of the substrate is shielded by the catalyst, pinpointing the origin or stereoselectivity for downstream transformations.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | DIELS-ALDER REACTION; MECHANISM; IMINES; 3,3'-SUBSTITUENTS; |
| 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 Physikalische und Theoretische Chemie > Chair of Chemistry VI - Physical Chemistry (Solution Chemistry) > Prof. Dr. Dominik Horinek |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 13 Feb 2024 07:36 |
| Last Modified: | 13 Feb 2024 07:36 |
| URI: | https://pred.uni-regensburg.de/id/eprint/56577 |
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