The Application Of Semi-azacrown Ether Chiral Ligand In The Asymmetric Copolymerization Reaction And Friedel–Crafts Alkylation Reaction

1. We have demonstrated the use of intramolecular dinuclear zinc-Aze Phenol catalyst generated in situ in the copolymerization of epoxides and CO₂ to afford completely alternating polycarbonates with excellent enantioselectivity. This dinuclear zinc catalyst is prepared in situ from the reaction of multidentate semi-azacrown ether ligand（S,S）-1 and Zn Et₂, followed by treatment with an alcohol additive.Catalyst screening and reaction condition optimization including solvent, temperature, and additive were investigated systematically. Positive nonlinear effect exists in the copolymerization of CO₂ and epoxides. The chemical structures of polymers are characterized by ¹H NMR, ¹³ C NMR spectroscopy, DSC, and WAXD analysis. It was recognized that the real catalytically active species was complex Zn₂ OEt L according to the structure analysis of PCPC and the positive nonlinear effect study in this copolymerization. Meanwhile, a plausible mechanism was tentatively put forward to explain the origin of the asymmetric induction supported by the DFT calculations of the energies of transition states TSCPO-re and TSCPO-si which were the stereoselectivity-determining step and the rate-determining step.In the presence of 5 mol %（S,S）-1, 10 mol % Zn Et₂, and 2 mol % Et OH additive, the copolymerization of epoxides and CO₂ can be accomplished under mild conditions under 1 atm pressure of CO₂ affording completely alternating copolymers for（S,S）-configuration. Substrate scope screening showed that the copolymerization of CHO, CHEO, and CXO with CO₂ went on smoothly affording PCHC（quantitative yield, 93.8% ee）, PCPC（98% yield, >99% ee）, PCHEC（62% yield, 86.9% ee）, and PCXC（62% yield, 94.4% ee）, respectively. To our knowledge, this study represents the first example of an intramolecular dinuclear zinc catalytic asymmetric copolymerization of CO₂ and several epoxides with excellent enantioselectivity, which represents a significant advantage over most zinc-catalytic systems developed for this reaction so far.2. A catalytic asymmetric Friedel–Crafts alkylation of unprotected pyrrole with a variety of differently substituted chalcones promoted by a dinuclear zinc complex Zn₂ Et L has been demonstrated. The Zn₂ Et L system was prepared in situ by reacting the chiral ligand（S,S）-1 with two equivalents of diethylzinc. A series of β-pyrrole-substituted dihydrochalcones were usually formed mostly in excellent yields（up to 99%） and excellent enantioselectivity [up to 99% enantiomeric excess（ee）] by using 15 mol % catalyst loading under mild conditions. A novel negative nonlinear effect was observed and discussed, meanwhile, according to kinitic studies and the other experimental results; a proposed mechanism was put forward to explain the origin of the asymmetric induction. To our knowledge, this study represents the first example of an enantioselective dinuclear zinc catalytic Friedel-Crafts reaction of unprotected pyrrole with chalcones with excellent results.