The Application Of Chiral Oxazoline-Imidazoline Ligands In Lewis Acid-Catalyzed Asymmetric Reactions

Asymmetric catalysis with chiral Lewis acid have emerged as one of the most successful and powerful tools in construction of carbon-carbon bonds, such as asymmetric Friedel-Crafts reaction, Henry reaction, Michael reaction, and so on. Such catalysts could easily coordirate or couple with reagents, and showed good enantioselectivity in many reactions. The paper utilized the known methods to synthesize a series of chiral oxazoline-imidazoline ligands, then these ligands was successfully complexed with Lewis acid and applied to the asymmetric Frediel-Crafts alkylation reaction and Henry reaction, the corresponding chiral product was obtained in good to excellent enantioselectivity and yield.1. Synthesis of chiral ligands L.(Scheme1)2. The application of ligands in Friedel-Crafts reaction.(Scheme2)1) The asymmetric reaction of indoles and N-sulfonyl iminesWe utilized copper trifluoromethanesulphonate as a Lewis acid, indole and N-sulfonamide as a template reaction. After surveying a variety of chiral center, the electronic effects and so on. We found that the combination of15mol%L5-10mol%Cu(OTf)2,2ml CH2Cl2,100mg4A MS,0℃,72h, under Ar served as the optimal conditions for this transformation, up to97%ee and95%yield of the product was obtained.2) Asymmetric reaction of aromatic ethers and N,N-disubstitutes aromatic amines with trifluoroacetic pyruvatePreliminary exploration and research through the adjusting reaction conditions of anisole and ethyl trifluoroacetic pyruvate to optimize the condition:In the presence of10mol%catalyst L1-Cu(OTf)2and solvent-free conditons, the transformation could be occured in up to84%ee and95%yield.3) The application of chiral ligands in asymmetric Henry reaction (Scheme3)Optimization the experimental conditions of nitromethane with aldehydes. Under the following conditions:6mol%L5-5mol%Cu(OAc)2·H2O, EtOH,15℃. It could get the moderate yield and enantioselectivity.