Asymmetric Reactions. X. Asymmetric Hydrogenation Catalyzed by Bis(dimethylglyoximato)cobalt(II)–Chiral Cocatalyst (Amino Alcohol) System
- 1 July 1981
- journal article
- research article
- Published by Oxford University Press (OUP) in Bulletin of the Chemical Society of Japan
- Vol. 54 (7), 2124-2135
- https://doi.org/10.1246/bcsj.54.2124
Abstract
The catalytic asymmetric hydrogenations of α-diketones, α-keto carboxylates, α-(acylamino)acrylates, α-phenylacrylophenone, and α-phenylacrylate were examined with bis(dimethylglyoximato)cobalt(II)–chiral cocatalyst (amino alcohol) and with simple achiral base coordinated bis(dimethylglyoximato)cobalt(II)–chiral cocatalyst (amino alcohol) systems. These gave corresponding optically active reduction products, and in some cases, optically active reductive dimerization products. High degrees of enantioselectivities (≈78%) are achieved in the hydrogenation of α-diketones. Evidence for non-binding of chiral base to cobalt complexes was presented in the case of latter system, i.e., it was shown that the catalytic site and the enantioselectivity-determining site are separated in this system, as in enzymes. The importance of protonated chiral bases for enantioselection was also shown. Based on these results and the stereochemical correlations between structures of the chiral bases and those of the products, a mechanism for this asymmetric hydrogenation was proposed.Keywords
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