Renzi, Polyssena and Hioe, Johnny and Gschwind, Ruth M. (2017) Decrypting Transition States by Light: Photoisomerization as a Mechanistic Tool in Bronsted Acid Catalysis. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 139 (19). pp. 6752-6760. ISSN 0002-7863,
Full text not available from this repository. (Request a copy)Abstract
Despite the wide applicability of enantioselective Bronsted acid catalysis, experimental insight into transition states is Very rare, and most of the mechanistic knowledge is gained by theoretical calculations. Here, we present an alternative approach (decrypting transition state by light = DTS-hv), which enables the decryption of the transition states involved in chiral phosphoric acids catalyzed addition of nucleophiles to imines. Photoisomerization of double bonds is employed as a mechanistic tool. For this class of reactions four pathways (Type I Z, Type I E, Type II Z, Type II E) are possible, leading to different enantiomers depending on the imine configuration (E- or Z-imine) and on the nucleophilic attack site (top or bottom). We demonstrated that the imine double bond can be isomerized by light (365 nm LED) during the reaction leading to a characteristic fingerprint pattern of changes in reaction rate and enantioselectivity. This characteristic fingerprint pattern is directly correlated to the transition states involved in the transformation. Type I Z and Type II Z are demonstrated to be the competing pathways for the asymmetric transfer hydrogenation of ketimines, while in the nucleophilic addition of acetylacetone to N-Boc protected aldimines Type I E and Type II E are active. Accelerations on reaction rate up to 177% were observed for ketimines reduction. Our experimental findings are supported by quantum chemical calculations and noncovalent interaction analysis.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | TRANSFER HYDROGENATION; PHOSPHORIC-ACIDS; BOND ROTATION; IMINES; ACTIVATION; POWERFUL; ENANTIOSELECTIVITY; PHOTOREDUCTION; ISOMERIZATION; PHOSPHATES; |
| 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: | 14 Dec 2018 13:10 |
| Last Modified: | 20 Feb 2019 07:01 |
| URI: | https://pred.uni-regensburg.de/id/eprint/877 |
Actions (login required)
 |
View Item |
