Asymmetric Hydrogenation Catalyzed by the (Achiral Base)bis(dimethylglyoximato)cobalt(II)–Chiral Cocatalyst System. The Preparation of a New Type of Chiral Cocatalyst and Its Application to the Asymmetric Hydrogenation of Methyl N-(Acetylamino)acrylate and Benzil

Abstract

Abstract As a new type of chiral cocatalyst in the achiral base-coordinated bis(dimethylglyoximato)cobalt(II)–chiral cocatalyst system, tertiary amines with an amide group at α- or β-carbon were prepared, and asymmetric hydrogenation was examined by using them. The optical yield reached 34.5% enantiomeric excess(ee) by using N-[(2S,3S)-2-acetoxy-3-dimetnylamino-3-phenylpropionyl]-(R)-α-methylbenzylamine; this is the highest value attained so far in the asymmetric hydrogenation of methyl N-(acetylamino)acrylate with this system. The enantioselectivity in the hydrogenation of methyl N-(acetylamino)acrylate was reversed with a configurational alteration of the α-methylbenzylamine moiety of N-[N,N-dimethyl-(S)-phenylalanyl]-α-methylbenzylamine, while it was not reversed in the hydrogenation of benzil by the configurational alteration. From these facts, it is deduced that the hydrogen bond between amide groups of the chiral amino carboxamides and methyl N-(acetylamino)acrylate may act as an attractive force to enhance the enantioselectivity of the asymmetric hydrogenation.