Polymer-grafted Ti-TADDOL complexes. Preparation and use as catalysts in Diels-Alder reactions

Different strategies have been evaluated for the preparation of polymers functionalized with chiral fragments containing the alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5 -dimethanol (TADDOL) structure. Best results are obtained when TADDOL derivatives containing OH phenolic groups (17 and 18) are prepared in solution and then selectively anchored to chloromethylated polymers by reaction in THF containing NaH and small amounts of 18C6 and NBu4I. Resins 19 having the desired functionality have been prepared in this way. The procedure allows the efficient introduction of this functional group in PS-DVB polymers with different loading and cross-linking degrees, as well as on SMOP resins. These functionalized resins have been used to prepare Ti-TADDOL-supported complexes which have been tested as catalysts in the reaction of cyclopentadiene with 3-crotonoyl-1,3-oxazolidin-2-one. Although all the polymers obtained efficiently catalyze the reaction, only the one prepared from alpha,alpha,alpha',alpha'-tetra-3,5-dimethylphenyl-1,3-dioxolane-4,5-dimethanol induces asymmetry.