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Asymmetric Diethyl‐ and Diphenylzinc Additions to Aldehydes by Using a Fluorine‐Containing Chiral Amino Alcohol: A Striking Temperature Effect on the Enantioselectivity, a Minimal Amino Alcohol Loading, and an Efficient Recycling of the Amino Alcohol
Author(s) -
Park Jin Kyoon,
Lee Hong Geun,
Bolm Carsten,
Kim B. Moon
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200400703
Subject(s) - chemistry , alcohol , solvent , hexane , enantioselective synthesis , enantiomer , catalysis , benzaldehyde , enantiomeric excess , reagent , chiral ligand , organic chemistry , reactivity (psychology) , amino acid , medicinal chemistry , medicine , alternative medicine , pathology , biochemistry
A chiral pyrrolidinylmethanol derivative containing perfluoro‐ponytails ( 5 ) was prepared from ( S )‐proline. The use of this perfluoro‐substituted amino alcohol in catalytic asymmetric additions of organozinc reagents to aldehydes affords products with high enantioselectivities in both pure hexane and a mixture of hexane and FC‐72 (perfluorohexane). Enantiomeric excesses up to 94 and 88 % ee have been achieved in Et 2 Zn and Ph 2 Zn additions, respectively. For the reactions in the biphasic solvent system a striking temperature effect was observed. Thus, when the temperature was raised from 0 to 40 °C the ee value of the product increased from 81 to 92 %. Furthermore, the catalyst loading could be remarkably low, and with only 0.1 mol % of amino alcohol 5 a product with 90 % ee was obtained in the Et 2 Zn addition to benzaldehyde in hexane. The perfluoro‐ligand was easily recovered by simple phase separation, and until the ninth repetition its reuse proceeded without significant loss of enantioselectivity and reactivity.