Synthesis of Enantioenriched α,α-Dichloro- and α,α-Difluoro-β-Hydroxy Esters and Amides by Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation

A mild and convenient approach was developed to prepare a series of alpha,alpha-dihalogeno beta-hydroxy esters or amides by using commercially available Noyori's complex [RuCl(p-cymene)(R,R)-TsDPEN] as a catalyst (S/C = 100-200) in the asymmetric transfer hydrogenation of the corresponding ketones. Moderate to high yields (up to 99%) and excellent enantioselectivities (up to >99% ee) were achieved for a series of variously substituted dichloro and difluoro beta-hydroxy esters and amides.