Microgel-bound oxazaborolidines have been prepared and used as catalysts in
the enantioselective reduction of prochiral ketones. The preparation of th
ese soluble, crosslinked polymer molecules was accomplished by solution pol
ymerisation. The approach involved the preparation of microgels bearing fre
e boronic acid functionalities and their subsequent conversion to oxazaboro
lidines. The selectivities of these supported catalysts are in most cases c
omparable to those achieved with low molecular weight analogues. The advant
age of the application of microgel-bound catalysts is their good solubility
together with low viscosity of the solution. Reagents of this type can eas
ily be removed by ultrafiltration and the process can be performed in a con
tinuous mode in a membrane reactor. (C) 2000 Published by Elsevier Science
Ltd. All rights reserved.