Known techniques for asymmetrically synthesizing optically active alcohols include a process comprising asymmetric hydrogenation using baker's yeast and a process comprising asymmetric hydrogenation using a specific catalyst.
In particular, with respect to asymmetric hydrogenation of an l-keto acid derivative to obtain optically active alcohols, it has been reported that the asymmetric hydrogenation can be carried out by using a rhodium-optically active phosphine complex as a catalyst. For example, J. Solodar reports in Chemtech., 421-423 (1975) that asymmetric hydrogenation of methyl acetoacetate gives methyl 3-hydroxybutyrate in an optical yield of 71% ee.
Further, asymmetric hydrogenation using a tartaric acid-modified nickel catalyst has been proposed. According to this technique, asymmetric hydrogenation of methyl acetoacetate gives methyl 3-hydroxybutyrate in an optical yield of 85% ee as disclosed in Tai, Yukagaku, 822-831 (1980).
Although the process using baker's yeast produces an alcohol having relatively high optical purity, the resulting optically active alcohol is limited in absolute configuration, and synthesis of an enantiomer is difficult.
The process utilizing asymmetric hydrogenation of a .beta.-keto acid derivative in the presence of a rhodium-optically active phosphine complex does not produce an alcohol having sufficient optical purity. Besides, metallic rhodium to be used in the catalyst is expensive due to limitations in place and quantity of production. When used as a catalyst component, it forms a large proportion in cost of the catalyst, ultimately resulting in increase in cost of the final commercial products.
The process using a tartaric acid-modified nickel catalyst involves disadvantages of difficulty in preparing the catalyst and insufficient optical yield.