Chiral Aziridine Sulfide <i>N(sp3),S</i>-Ligands for Metal-Catalyzed Asymmetric Reactions

Abstract

A series of new bidentate N,S-ligands—aziridines containing a para-substituted phenyl sulfide group—was synthesized and evaluated in the Pd-catalyzed Tsuji–Trost reaction and addition of diethylzinc and phenylethynylzinc to benzaldehyde. A high enantiomeric ratio for the addition reactions (up to 94.2:5.8) was obtained using the aziridine ligand bearing a p-nitro phenyl sulfide group. Collected results reveal a specific electronic effect that, by the presence of particular electron-donating or electron-withdrawing groups in the PhS- moiety, influences the σ-donor–metal binding and the enantioselectivity of the catalyzed reactions.

Keywords

• aziridine
• <i>N,S</i>-ligands
• asymmetric synthesis
• diethylzinc addition
• phenylethynylzinc addition
• Tsuji–Trost reaction