title: 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.
abstract: 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 degrees 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.
authors.affiliation: School of Chemistry, Seoul National University, Seoul 151-747, South Korea.
authors.forename: Jin Kyoon
authors.initials: JK
authors.lastname: Park
authors.forename: Hong Geun
authors.initials: HG
authors.lastname: Lee
authors.forename: Carsten
authors.initials: C
authors.lastname: Bolm
authors.forename: B Moon
authors.initials: BM
authors.lastname: Kim
mesh_terms: D000447:Aldehydes / Q000737:chemistry*; D000605:Amino Alcohols / Q000737:chemistry*; D005461:Fluorine / Q000737:chemistry*; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D013237:Stereoisomerism; D013696:Temperature; D015032:Zinc / Q000737:chemistry*
chemical_list: D000447:Aldehydes; D000605:Amino Alcohols; D009942:Organometallic Compounds; C511645:diphenylzinc; D005461:Fluorine; D015032:Zinc; C454811:diethylzinc