Microgel-supported oxazaborolidines: Novel catalysts for enantioselective reductions

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.