Journal of Catalysis, Vol.361, 398-406, 2018
Synthesis of chiral polyesters of cinchona alkaloid catalysts for enantioselective Michael addition of anthrone to nitroalkenes
Chiral polyesters of cinchona alkaloid derivatives were synthesized via repetitive Mizoroki-Heck (MH) coupling reaction. Under MH reaction conditions, 4-iodobenzoylquinine and 4-iodobenzoylcupreine were easily polymerized via self polycondensation to afford the corresponding chiral polyesters. The MH reaction conditions were also applied to the two-component polycondensation of cinchona ester dimer and aromatic diiodide to obtain the chiral polyesters. These cinchona-based chiral polyesters were successfully applied as polymeric organocatalysts in the asymmetric Michael addition reaction. The chiral polyesters bearing free OH groups at the C6' position of the quinoline rings showed high catalytic activities (up to 97% isolated yield) and good enantioselectivities (up to 92% ee) in the Michael addition of anthrone to nitroalkenes. Furthermore, these polymeric catalysts were stable and could be recycled and reused several times. (C) 2018 Elsevier Inc. All rights reserved.
Keywords:Cinchona alkaloids;Mizoroki-Heck polymerization;Polycondensation;Chiral polyester;Organocatalysts;Asymmetric catalysis