HIGHLY EFFICIENT HETEROGENEOUS POLYMER-SUPPORTED SHARPLESS ALKENE EPOXIDATION CATALYSTS

More widespread, and cost effective, use of soluble transition metal c omplex asymmetric catalysts would be achieved if highly efficient hete rogeneous analogues could be developed. We now report the synthesis of branched/crosslinked poly(tartrate ester)s and their use as heterogen eous ligands for the complexation of Ti((OPr)-Pr-i)(4), and use of the resulting insoluble catalysts in the asymmetric epoxidation of a rang e of trans-allylic alcohols employing t-butylhydroperoxide (tBHP) as t he oxidant. Isolated yields of epoxides of up to 80%, with enantiomeri c excesses up to 98% have been achieved. Removal and recovery of the p olymer catalyst is by simple filtration at the end of reactions. The i nfluence of the ratio of polymer-ligand-titanium, and the polymer back bone molecular architecture on the activity and enantioselectivity of the catalysts has been assessed. Typically polymer branching ratios of 3-11% and a polymer-ligand:titanium ratio of 2:1 yield the optimum re sults. (C) 1998 Elsevier Science Ltd. All rights reserved.