Homogeneous Asymmetric Hydrogenation and Hydrosilylation of Keto Esters Catalyzed by Chiral Rhodium Complexes

Abstract

Although the homogeneous hydrogenation of carbon-carbon multiple bonds catalyzed by various transition metal complexes has been extensively studied,1 e.g., asymmetric hydrogenation of acetamidocinnamic acid is a great success,2 that of carbon-oxygen double bonds has received relatively little attention. Thus, there had been only a few papers3 before Schrock and Osborn reported4 in 1970 that cationic rhodium complexes with relatively basic phosphines as ligands catalyze the reduction of ketones under mild conditions. This is partly due to the fact that the Wilkinson’s type non-cationic rhodium(l) complexes lack activity toward the hydrogenation of carbonyl functionalities5 and that these complexes also catalyze the decarbonylation of carbonyl compounds, especially of aldehydes.5,6 On the basis of these findings a catalytic asymmetric hydrogenation of ketones has been achieved with low optical yields in 1972.7 Along this line, Solodar reported a good result on the asymmetric hydrogenation of methyl acetoacetate.8 Ohgo and coworkers also reported the asymmetric homogeneous hydrogenation of carbonyl groups with Co(dimethylglyoxymato)2 (quinine)(benzylamine) as a catalyst, but except for the rather special case of the reduction of benzil to benzoin, the product alcohols were obtained with a low enantiomeric excess.9