Chiral sulfur-containing ligands for iridium(I)-catalyzed asymmetric transfer hydrogenation of aromatic ketones

New efficient catalyst systems, coupled with IrCl(COD)PPh3 and chiral [SNNS]-type ligands, were employed in the asymmetric transfer hydrogenation of aromatic ketones under mild reaction conditions. The corresponding optically active alcohols were obtained in high yield and good to excellent enantioselectivities (up to 96% ee). The chiral Ir(I) complexes with the ligands of [SNNS]-type were also prepared and characterized, which showed good enantioselectivity and high activity. The reactions can be performed in air and the catalytic experiments are greatly simplified.

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(1R,2R)-N1,N2-Bis(thiophen-2-ylmethyl)cyclohexane-1,2-diamineC16H22N2S2Mp 57 °C[α]D20=-102.0 (c 0.5, CH3OH)Source of chirality: asymmetric synthesisAbsolute configuration: (1R, 2R)