The Applications Of Imidazoline-Oxazoline Ligands In The Asymmetric Michael Addition And Friedel-Crafts Alkylation Reaction

The catalysis of asymmetric Michael reactions and Friedel-Crafts reactions by metals can be considered as one of the powerful tools for the stereocontrolled formation of chiral centre. By the very fact of the lower costs and toxicity of cobalt and nickel catalysts, ecological and economical cobalt/nickel-mediated transformations have received continuous ever-growing attention during the last two decades. The excellent enantioselective construction of trifluoromethylated all-carbon quaternary stereocenters has been much less exploited and remains a very important and extremely challenging task in asymmetric catalysis. In this thesis, five chiral imidazoline-oxazoline ligands have been synthesized with the known methods. Then these ligands were successfully complexed with Co(II)/ Ni(II) and applied to the asymmetric Michael reaction and Frediel-Crafts alkylation reaction, forming trifluoromethylated all-carbon quaternary stereocenters in good yields with excellent enantioselectivities. The main results are as follows:1. The asymmetric Michael addition of 2-acetyl azaarenes withβ-CF3-β-disubtituted nitroalkenes.The catalytic properties of the five chiral L-Co(II) complexes in the asymmetric Michael addition of 2-acetyl azaarenes with a variety of β-CF3-β-disubtituted nitroalkenes were investigated. Results show that under the condition of 12 mol%chiral ligand L1 and 10 mol% Co(acac)2, MTBE(1.5 mL) as solvent and 20 oC, the optically active adducts could been successfully prepared with up to 99% yield and98% ee(Scheme 2).2. The asymmetric Friedel-Crafts alkylation reaction of β-CF3-β-disubstituted nitroalkenes and indoles.The catalytic properties of the five chiral ligands L-Ni(II) complexes in the asymmetric Friedel-Crafts alkylation reaction of β-CF3-β-disubstituted nitroalkenes and indoles were investigated. Results indicate that in the presence of 6 mol% L1-5mol% Ni(ClO4)2?6H2O catalyst loading, toluene(4 mL) as solvent and 80 o C, the corresponding optically active products were successfully prepared with high yields(95%) and 95% ee(Scheme 3).