Li, Xinyao and Kutta, Roger J. and Jandl, Christian and Bauer, Andreas and Nuernberger, Patrick and Bach, Thorsten (2020) Photochemically Induced Ring Opening of Spirocyclopropyl Oxindoles: Evidence for a Triplet 1,3-Diradical Intermediate and Deracemization by a Chiral Sensitizer. ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 59 (48). pp. 21640-21647. ISSN 1433-7851, 1521-3773
Full text not available from this repository. (Request a copy)Abstract
The photochemical deracemization of spiro[cyclopropane-1,3 '-indolin]-2 '-ones (spirocyclopropyl oxindoles) was studied. The corresponding 2,2-dichloro compound is configurationally labile upon direct irradiation at lambda=350 nm and upon irradiation at lambda=405 nm in the presence of achiral thioxanthen-9-one as the sensitizer. The triplet 1,3-diradical intermediate generated in the latter reaction was detected by transient absorption spectroscopy and its lifetime determined (tau=22 mu s). Using a chiral thioxanthone or xanthone, with a lactam hydrogen bonding site as a photosensitizer, allowed the deracemization of differently substituted chiral spirocyclopropyl oxindoles with yields of 65-98 % and in 50-85 %ee(17 examples). Three mechanistic contributions were identified to co-act favorably for high enantioselectivity: the difference in binding constants to the chiral thioxanthone, the smaller molecular distance in the complex of the minor enantiomer, and the lifetime of the intermediate 1,3-diradical.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | CATALYTIC ASYMMETRIC-SYNTHESIS; ENERGY-TRANSFER; ENANTIODIFFERENTIATING PHOTOISOMERIZATION; ENHANCED DIASTEREOSELECTIVITY; CYCLIZATION REACTIONS; EXCITED THIOXANTHONE; INTERNAL-CONVERSION; CHIMERIC BEHAVIOR; PRODUCT CHIRALITY; CYCLOPROPANATION; enantioselectivity; hydrogen bonds; photochemistry; time-resolved spectroscopy; xanthones |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Physical Chemistry I Chemistry and Pharmacy > Institut für Physikalische und Theoretische Chemie > Chair of Physical Chemistry I > Prof. Dr. Patrick Nürnberger |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 11 Mar 2021 12:02 |
| Last Modified: | 11 Mar 2021 12:02 |
| URI: | https://pred.uni-regensburg.de/id/eprint/43783 |
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