Increasing enantioselectivity and reactivity in Ir-Catalysed intramolecular hydroamination reactions

Abstract

A series of axially chiral NHC ligands bearing dialkylated naphthyl side arms and electron-rich substituted phenyl groups in the backbone have been employed in the synthesis of neutral NHC-Ir(COD)Cl complexes. When the halide ligand was abstracted from these compounds by appropriate silver salts AgX (X = PF6, NTf2), chiral cationic, formally 14-electron iridium complexes [(NHC)Ir(COD)][X] were formed. When these species were applied as catalysts for asymmetric intramolecular hydroamination of unactivated, amino-olefin substrates, chiral 5- and 6- membered N-heterocyclic products were obtained with moderate to excellent enantioselectivities. By tuning the substrate through variation of the N-protecting group on the amino-olefin substrates, remarkable improvements in enantioselectivity were obtained.