Polymer-assisted asymmetric reactions. III. The use of crosslinked polymers containing chiral amino-alcohol or polyol pendant groups in asymmetric hydride reductions

Several new polymers containing chiral amino-alcohol or hydroxy pendant groups have been prepared by chemical modification of crosslinked halomethylated polystyrene resins. The polymers are used as chiral auxiliaries in the asymmetric reduction of prochiral ketones using partially deactivated lithium aluminium hydride. It is found that the stereochemical outcome of the asymmetric synthesis is affected greatly by factors such as steric hindrance, nature and amount of the achiral additive used, and structure of the chiral auxiliaries. A comparison of the performance of the polymers with chiral model compound reveals that although the polymers are easier to use, higher optical yields can be obtained with the model compounds.