Asymmetric reduction of ketones via whole cell bioconversions and transfer hydrogenation: complementary approaches

Prochiral aryl and dialkyl ketones were enantioselectively recduced to the corresponding alcohols using whole cells of the white-rot fungus Merulius tremellosus ono91 as a biocatalytic reduction system and ruthenium(II)amino alcohol and iridium(I)-amino sulfide complexes as metal catalysts in asymmetric transfer hydrogenation. Comparison of the results showed that the corresponding chiral alcohols could be obtained with moderate to high enantioselectivities (e.e.s of up to 98%). The biocatalytic and transfer hydrogenation approaches appear to he complementary. The biocatalytic approach is the most suitable for the enantioselective reduction of chloro-substituted (aryl) ketones, whereas in the reduction of alpha,beta -unsaturated compounds excellent results were obtained using the catalytic hydrogenation protocol. (C) 2001 Elsevier Science Ltd. All rights reserved.