Effect of polymer-supported catalytic moiety on an asymmetric ethylation of aldehyde by diethylzinc

In order to investigate their effects on an asymmetric alkylation of aldehyde by diethylzinc, two types of polymer-supported asymmetric catalysts derived from chiral amino alcohols were prepared by two different preparation techniques. As reference catalysts, corresponding monomeric and unbound polymeric catalysts were also prepared. The monomeric catalysts showed moderate enantioselectivities in hexane, however, the unbound polymeric catalysts prepared by polymerization of the monomeric catalysts afforded quite low enantioselectivities in hexane. Immobilized catalysts prepared by classical copolymerization technique showed similar catalytic selectivities as the monomeric catalysts, on the other hand, anchored-type polymer-supported catalysts afforded similar catalytic selectivities to those of the unbound polymeric catalysts. These observations suggested that difference in preparation techniques should afford immobilized catalysts involving different catalytic moieties just like monomeric catalyst or unbound polymeric catalyst which somehow affects asymmetric reactions.