Schaetz, Alexander and Rasappan, Ramesh and Hager, Markus and Gissibl, Anja and Reiser, Oliver (2008) Dependence of enantioselectivity on the ligand/metal ratio in the asymmetric Michael addition of indole to benzylidene malonates: Electronic influence of substrates. CHEMISTRY-A EUROPEAN JOURNAL, 14 (24). pp. 7259-7265. ISSN 0947-6539,
Full text not available from this repository. (Request a copy)Abstract
Simple bis(oxazoline) ligands, especially azabis(oxazolines), call promote the copper(II)-catalyzed Michael addition of indoles to benzylidene malonates with up to > 99% ee (ee = enantiomeric excess), provided that the ligand/metal ratio is tuned meticulously With particular regard to the electronic properties of the Substrate. Despite a common paradigm followed in many asymmetric catalyses, an excess of chiral ligand is not always beneficial. In fact any excess of ligand has to be avoided to reach excellent enantioselectivities when electron-rich benzylidene malonates are used. On the contrary, malonates carrying all electron-withdrawing group require an excess of ligand for all Optimum ee value. A correlation of optical yields versus the sigma(I) values of several para substituents shows a signioid trajectory. In the presence of in additive. such as triflate, the significance of the ligand/metal ratio vanishes and very good enantioselectivities are achieved at any rate-no matter whether electron-donating or withdrawing substituents are present.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | FRIEDEL-CRAFTS ALKYLATION; CHIRAL LEWIS-ACIDS; COPPER(II) COMPLEXES; CONJUGATE ADDITION; CATALYSIS; LIGANDS; TRISOXAZOLINE; COORDINATION; DERIVATIVES; OLEFINS; asymmetric catalysis; enantioselectivity; homogeneous catalysis; Michael addition; oxazoline ligands |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Organische Chemie Chemistry and Pharmacy > Institut für Organische Chemie > Lehrstuhl Prof. Dr. Oliver Reiser |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 11 Nov 2020 10:03 |
| Last Modified: | 11 Nov 2020 10:03 |
| URI: | https://pred.uni-regensburg.de/id/eprint/31583 |
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