The Synthesis Of Polymers Derived From BINOL And Application In Asymmetric Addition Of Aldehydes

Since the 1980 s, optical active 1,1’-bi-2-naphthol(BINOL) was widely used in various kinds of organic asymmetric reactions which have got great achievement rapidly. As research continued, the disadvantage of small molecular catalysts with binaphthalene unit appeared gradually in asymmetric reactions. To overcome the disadvantage of small molecule catalyst, which is difficult for recycle and separation, we designed and synthesized a series of chiral macromolecular ligand derived from BINOL. In order to study their catalytic ability, we applied these macromolecular ligands to induce the asymmetric addtion of aldehydes. As the result, we obtained a series of chiral secondary alcohols.(1)(S)-3-hydroxy-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol was created. With the dehydrogenation of NaH,(S)-3-hydroxy-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol reacted with vinylbenzyl chloride to give the monomer(S)-3-4-vinylbenzyloxy-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol. Poly[(S)-3-4-Vinylbenzyloxy-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol](poly-2) was given by radical polymerization with AlBN as the initiator. By deprotection of the MOM groups, poly[(S)-3-4-vinylbenzyloxy-1,1’-bi-2-naphthol](poly-3) was obtained. Poly-3 was used as a asymmetric conductor of the addition of Et2 Zn to aromatic aldehydes. The products were obtained in good enantioselectivity with up to 89% ee, the yields were good too(up to 97%). Poly-3 exhibited activity even after being used several times.(2) With Pd(PPh3)4 as the catalyst,(S)-3-iodo-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol reacted with 4-vinyphenyl boronic acid to afford the monomer(S)-3-(4-vinyphenyl)-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol by the coupled reaction. Monomer(S)-6-(4-vinyphenyl)-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol was obtained by the coupled reaction of(S)-6-(bromo)-2,2’-bis(methoxymethyl)-1,1’-bi-2-naphthol with 4-vinyphenyl boronic acid. Poly-4a、poly-4b、poly-4c、poly-9 were obtained by free radical copolymerization of the two monomers with different proportions of styrene. By deprotection of the MOM groups of poly-4a、poly-4b、poly-4c、poly-9, polymeric ligands poly-5a(loading 1.15 mmol/g)、poly-5b(loading 0.74 mmol/g)、poly-5c(loading 0.36 mmol/g)、poly-10(loading 0.73 mmol/g) was given. All polymeric ligands were applied to in the asymmetric addition reaction of Et3 Al to aldehydes. The products are obtained in excellent yields(up to 96%) with high enantioselectivities(up to 93%), poly-5a exhibited high activity even after being used several times. To investigate the further catalytic activity of ligand poly-5a, poly-5a was applied in the asymmetric methylation of aldehydes with trimethyl aluminum as the methylating reagent, the products are obtained in good yields(up to 85%) with moderate enantioselectivities(up to 44%), poly-5a could be reused in this reaction too.