Brunner, Henri and Stoehr, Frank (2000) Asymmetric catalysis, 132 - Metal-catalyzed enantioselective alpha-ketol rearrangements. EUROPEAN JOURNAL OF ORGANIC CHEMISTRY (15). pp. 2777-2786. ISSN 1434-193X
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Promoted by catalytic amounts of transition-metal complexes, the tertiary alpha-hydroxy ketones 1, 3, 5/6 undergo alpha-ketol rearrangements to afford equilibrium mixtures of isomers with a reorganization of the carbon skeleton. The range of metal complexes catalyzing the isomerizations is large; the best results were obtained with the catalyst systems NiCl2/TMEDA, Ni(acac)(2), and Ni(acac)(2),TMEDA (TMEDA N, N, N', N'-tetramethyl-1, 2-diaminoethane). The catalytic rearrangements were performed at 130 degrees C in the absence of solvent, with a Ni-II/ligand/substrate ratio of 1:2:100. The equilibrium composition of the model system 1/2 is 12.5:87:5. The conversion of the achiral substrates 1 and 3 into the chiral products 2 and 4 can be used for kinetic resolution However, the reverse reactions 2 --> 1 and 4 --> 3 in the equilibrations narrow the window for asymmetric induction with enantioselective catalysts of the metal component/optically active ligand type. In system 1, the highest enantiomeric excess was achieved with the catalyst systems NiCl2/pybox [18.9% (S)-2] and Ni(acac)(2)/pybox [19.3% (R)-2] {pybox = 2,6-bis[(S)-4-isopropyl(oxazolin-2'-yl)]pyridine}. The alpha-ketol rearrangement of 3 with the Ni(acac)(2)/pybox catalyst resulted in a maximum enantiomeric excess of 37.1% (S)-4.
| Item Type: | Article |
|---|---|
| Uncontrolled Keywords: | C-2 EPIMERIZATION; NICKEL(II) COMPLEXES; CARBON SKELETON; ALDOSES; IONS; MANNOSE; rearrangements; isomerizations; ketones; asymmetric catalysis |
| Subjects: | 500 Science > 540 Chemistry & allied sciences |
| Divisions: | Chemistry and Pharmacy > Institut für Anorganische Chemie > Alumni or Retired Professors > Prof. Dr. Henri Brunner |
| Depositing User: | Dr. Gernot Deinzer |
| Date Deposited: | 29 Mar 2022 08:13 |
| Last Modified: | 29 Mar 2022 08:13 |
| URI: | https://pred.uni-regensburg.de/id/eprint/42293 |
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