Synthesis of chiral polymers and its application in asymmetric reduction

Abstract

Two new cinchona alkaloids copolymers (PMA-BQTP and PMA-QN) have been synthesized by copolymerization and their complexes (PMA-BQTP-PdCl 2 and PMA-QN-PdCl 2 ) have been prepared. Their structures were characterized by FTIR, GPC, and element analysis. The catalytic activity of PMA-QN-PdCl 2 in the heterogeneous catalytic asymmetric reduction of aromatic ketone by sodium borohydride was studied. The results showed that the polymer complex catalyzed the reduction of aromatic ketone to get alcohol in high optical yield, but their catalytic efficiency was largely dependent on the aromatic ketone and solvent system, which relate to the accessibility of the catalytic active site. And the PdCl 2 /polymeric alkaloid complex can be simply recovered at the end of the reaction by centrifugation and then reused without serious losing of activity or enantioselectivity.

Recyclable Stereoselective Catalysts

“…The complex of this polymeric ligand with PdCl 2 , was tested for aromatic ketone reduction with sodium borohydride. The optical yield observed never rises above 65% ee, and this system showed efficient recyclability over five cycles …”

“…The optical yield observed never rises above 65% ee, and this system showed efficient recyclability over five cycles. 93 Vinodradov et al heterogenized the Ru-(S)-BINAP hydrogenation catalyst in a poly(diallyldimethylammonium salt). This heterogeneous catalyst was reused three times in methyl levulinate hydrogenation (S/C ) 200, 40 atm H 2 ) affording the respective alcohol with excellent enantioselectivities (>98% ee).…”

Cinchona Alkaloids as Chirality Transmitters in Metal‐Catalyzed Asymmetric Reductions

“…The results were later confirmed, but ee values never exceeded 50% [9]. Cha and colleagues [11] described the NaBH 4 reduction of a variety of substituted acetophenone derivatives catalyzed by Pd complexes of copolymers of methacrylate and Qn derivatives, but again enantioselectivity did not exceed 48%. The NaBH 4 reduction under phase-transfer conditions in the presence of an N-alkylated cinchona derivative as pioneered by Julia et al [6] was later taken up by Hofstetter et al [10], but ee values never exceeded 30%.…”

Polymeric cinchona alkaloids for the catalytic asymmetric dihydroxylation of olefins

“…The copolymers C (PMA‐BQTP), B (PMMA‐BQTP), and D (PAN‐BQTP) were synthesized by the same method as reported earlier 17. A solution of chiral monomer (BQTP, 1 mmol), second monomer (MA or MMA or AN, 40 mmol), and AIBN (0.1%) as initiator in dry benzene was refluxed for 72 h under dry nitrogen atmosphere at 70°C.…”