Synthesis and Asymmetric Enantioselective Addition of Chiral Polybinaphthyl and Polybinaphthol Ligands

Four chiral polymers P-1, P-2, P-3 and P-4 were synthesized by the polymerization of (S)-2,2′-dioctoxy-1,1′- binaphthyl-6,6′-boronic acid (S-M-3) with (S)-6,6′-dibromo-1,1′-binaphthol (S-M-1), (R)-6,6′-dibromo-1,1′- binaphthol (R-M-1), (S)-3,3′-diiodo-1,1′-binaphthol (S-M-2) and (R)-3,3′-diiodo-1,1′-binaphthol (R-M-2) under Pd-catalyzed Suzuki reaction, respectively. All four polymers can show good solubility in some common solvents due to the nonplanarity of the polymers in the main chain backbone and flexible alkyl groups in the side chain. The analysis results indicate that specific rotation and circular dichroism (CD) spectral signals of the alternative S-S chiral polymers P-1 and P-3 are larger than those of S-R chiral polymers P-2 and P-4, but their UV-Vis and fluorescence spectra are almost similar. The results of asymmetric enantioselectivity of four polymers for diethylzinc addition to benzaldehyde indicate that catalytically active center is (R) or (S)-1,1′-binaphthol moieties.