Asymmetric hydrogenation of 1-phenylpropane-1,2-dione over cinchona-modified Pt: Role of the C-9 OH group of cinchonidine

A1 Journal article (refereed)


Internal Authors/Editors


Publication Details

List of Authors: Toukoniitty E, Busygin I, Leino R, Murzin DY
Publisher: ACADEMIC PRESS INC ELSEVIER SCIENCE
Publication year: 2004
Journal: Journal of Catalysis
Journal acronym: J CATAL
Volume number: 227
Issue number: 1
Start page: 210
End page: 216
Number of pages: 7
ISSN: 0021-9517


Abstract

1-Phenylpropane-1,2-dione was hydrogenated over chirally modified 5% Pt/Al2O3 catalyst at 10 bar H-2 and 15degreesC using toluene and acetic acid as solvents. The highest enantiomeric excess for the major product (R)-1-hydroxy-1-phenyl-2-propanone (ee = 57%) was obtained using cinchonidine as the chiral modifier. The presence of the hydroxyl group in the C-9 position of the modifier was important for achieving high enantioselectivity. When the C-9 hydroxyl group of cinchonidine was replaced by a methoxy group enantioselectivity was lost and a small 2% excess of (S)-1-hydroxy-1-phenyl-2-propanone enantiomer was observed. In acetic acid the reaction with cinchonidine proceeded yielding a 7% excess of the (R)-product. Hydrogenation of the intermediate hydroxyketones in acetic acid using cinchonidine or 9-methoxy-10,11-dihydrocinchonidine as chiral modifiers gave the corresponding (1S,2R)-diol in 67 and 78% enantiomeric excesses, respectively. By changing the solvent from acetic acid to toluene, an inversion of enantioselectivity took place yielding the (1R,2S)-diol as the main product in 38% ee. A mechanism was proposed involving a two-step cycle (reactant-modifier) and a three-step cycle (reactant-modified acetic acid) in order to account for the observed enantioselectivities. (C) 2004 Elsevier Inc. All rights reserved.


Keywords

1-phenylpropane-1,2-dione, asymmetric hydrogenation, cinchonidine, diols

Last updated on 2019-19-10 at 03:22