POLYMER-SUPPORTED TADDOLS THROUGH PHENOLIC SPACERS AS LIGANDS OF TI(IV) FOR THE ENANTIOSELECTIVE DIELS-ALDER REACTION

Three phenolic TADDOLs 2-(p-hydroxyphenyl)-1,3-dioxolane-4,5-dimethano ls) are synthesised and grafted to several styrene-divinyl-benzene pol ymers possessing aliphatic drains of different length, n=1, 6 and 9. T he efficiency of the resulting chiral polymers as ligands of Ti(IV) in the Diels-Alder cycloaddition reaction of cyclopentadiene to 3-croton oyl-1,3-oxazolidin-2-one is studied and compared to that observed with their equivalent homogeneous catalysts. Only moderate enantioselectiv ities are obtained when the polymeric ligand with a methylenic spacer (n = 1) is used, the highest e.e. (53%) being reached with 15a. The re cycling of the heterogeneous catalysts is also studied.