Asymmetric hydrogenation of an α,β-unsaturated ketone by diamine(ether-phosphine)ruthenium(II) complexes and lipase-catalyzed kinetic resolution:: a consecutive approach

The RuCl2(eta(1)-Ph2PCH2CHOCH3)(2)(diamine) complexes 2L(1)-2L(5) have been prepared in high yields from the reaction of equimolar amounts of RuCl2(eta(2)-Ph2PCH2CH2OCH3)(2) 1 with various kinds of chelating diamines L-1-L-5 to form five-membered chelates with ruthenium. These novel ruthenium(II) complexes have been used as catalysts in the asymmetric hydrogenation of the prochiral ketone trans-4-phenyl-3-butene-2-one 3, using 2-propanol and different types of cocatalysts. Whereas complexes with achiral diamines afforded the racemic alcohols, complexes with chiral diamines (R,R or S,S) allowed the formation of the corresponding enantiomerically enriched secondary alcohol (S or R) with ee values of 45%. lit order to obtain the secondary alcohol with ee of >99%, the kinetic resolution of enantiornerically enriched trans-4-phenyl-3-butene-2-ol 3 was performed in a consecutive approach using either the lipase-catalyzed enantioselective transesterification of the alcohol with isoproperryl acetate as the acyl donor in toluene or the enantio selective hydrolysis of the corresponding acetate in buffer. The determination of the enantiomeric. excess (ee) of the resulting enantiornerically enriched secondary alcohols was performed by gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin as the chiral stationary phase. (C) 2003 Published by Elsevier Science Ltd.