Polymer-Supported Chiral Amino Acid Titanium Catalyze Asymmetric Diels-Alder Reaction

Polymer-supported chiral catalyst is a new type of catalyst with advantage of easy separation from reaction system, easy recovery and reusability. And the way of realizing asymmetric synthesis using supported catalysts has great potential and effect in development nowadays and makes great interest in organic chemistry. Taking amino acids as chiral ligands, we have synthetized polymer-supported chiral amino acid titanium complexes and used them to catalyze asymmetric Diels-Alder reation for the first time. This paper consists of four parts: 1. The synthesis of chiral monomers p-vinylbenzenesulfonyl- amino acid. p-vinylbenzene sulfonylchloride was obtained by treating sodium p-styrene sutfonate with thionyl chloride, the obtained product was reacted with four natural chiral amino acids (L-phenylalanine, L- valine, L-leucine, L-iso-leucine) to give four chiral monomers. 2. The synthesis of crosslinking agent bis (4-vinylbenyl) oligo- (ethylene glycol)s. 3. The synthesis of polymer-supported chiral amino acid titanium. The four polymer-supported chiral ligands were prepared by suspension copolymerization of the corresponding monomers with styrene and bis(4-vinylbenyl) oligo-(ethylene glycol)s as crosslinking agent. Treatment of the polymers with TiC14 gave four catalysts of polymer-supported chiral Sulfonylamino acid titanium complexes. 4. Through the asymmetric Diels-Alder reation of N-propenoyl- 1 ,3-oxazolidin-2-one with cyclopentadiene catalyzed by the supported catalyst, we studied the effect of reaction temperature, chiral ligand amino acid, the size of polymers beads on the yield and enantioselec- tivity of the endo cycloaddition adduct The experiment result showed that the supported chiral titanium complexes were of some catalytic activity and selectivity when they catalyzed the reaction of N-propenoyl- 1 ,3-oxazolidin-2-one with cyclopentadiene. And the catalysts could be recovered and reused. Owing to the large size of polymer beads and the existence of TiC 14, the highest enantioselectivity only reached to 17%, which is lower than the corresponding homogeneous system.