N-tert-Butanesulfinyl imine and aromatic tertiary amide derived non-biaryl atropisomers as chiral ligands for silver-catalyzed endo-selective [3+2] cycloaddition of azomethine ylides with maleimides

Simple modifications of our novel ligand (Xing-Phos) were presented in this work, and a series of aromatic tertiary amide derived non-biaryl atropisomers were successfully synthesized in good yields. In addition, it was found that the multifunctional aromatic tertiary amide derived non-biaryl atropisomers exhibited an excellent endo-selectivity in the silver-catalyzed [3+2]-cycloaddition of azomethine ylides with N-aromatic maleimide. And especially, good to high levels of enantioselectivity (up to 98% ee) was obtained with a wide range of substrates in the presence of syn-(R, R-S)-2a (Xing-Phos). Furthermore, on the basis of the experimental data, it was demonstrated that a trace amount of water play an important role in the enhancement of enantioselectivity. (C) 2015 Elsevier Ltd. All rights reserved.