Patent ID: 7538234

Claim:
A method for preparing an optically active 2-(1-hydroxyalkyl)-5-hydroxynaphtho[2,3-b]furan-4,9-dione compound of the formula (II): wherein R is C 1 -C 6 alkyl, comprising asymmetrically reducing a compound of the formula (I): wherein R is the same as defined above, in the presence of an asymmetric ruthenium complex and a hydrogen donor, wherein the asymmetric ruthenium complex is selected from the group consisting of Ru[(S,S)-Tsdpen](p-cymene) (chemical name: [(1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethanediamine]-(p-cymene) ruthenium (II)), RuCl[(S,S)-Tsdpen](p-cymene) (chemical name: chloro [(1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethanediamine]-(p-cymene) ruthenium (II)), RuCl[(S,S)-Tsdpen](mesitylene) (chemical name: chloro [(1S,2S)-N-(p-toluenesulfonyl)-1,2-diphenylethanediamine]-(mesitylene) ruthenium (II)) and RuCl[(S,S)-Msdpen](p-cymene) (chemical name: chloro[(1S,2S)-N-(methanesulfonyl)-1,2-diphenylethanediamine]-(p-cymene) ruthenium (II)).