A polymer-enlarged homogeneously soluble oxazaborolidine catalyst has been prepared and used in the enantioselective borane reduction of ketones. The catalyst is derived from (2S,4R)-alpha,alpha-diphenyl-2-[(4-allyloxy)-N-benzyloxycarbonyl]pyrrolidinemethanol 3 and a methyl hydrosiloxane-dimethylsiloxane copolymer 4 (15% functionalized). Enantioselective reduction of prochiral ketones to the corresponding chiral alcohols proceeds with enantiomeric excesses up to 98%. The catalyst can be retained by a nanofiltration membrane and thus could be recovered after reaction or used in a continuously operated membrane reactor. (C) 1997 Elsevier Science Ltd.