Asymmetric transfer hydrogenation of ferrocenyl ketones: a new simple route to chiral ferrocenyl alcohols

The asymmetric transfer hydrogenation (ATH) of ferrocenyl ketones, such as FcC(O)CH2Y [Fc = ferrocenyl, Y = H (1a), CH3 (1b), Cl (1c) or N-3 (1d)] has been carried out using the Noyori/Ikariya catalysts [(-)-(1R,2S)-ephedrine] or N-tosyl-(1R,2R)-diphenylethylenediamine [(R,R)-TsDPEN] as chiral ligands combined with [RuCl2(eta(6)-benzene)](2) and 2-PrOH or HCO2H-Et3N as the hydrogen sources, respectively. The best results were achieved with the [(R,R)-TsDPEN-(RuHCO2H)-H-II-Et3N] catalytic system, which produced the ferrocenylalcohols (R)-2a, (R)-2c, and (R)-2d in good yields and excellent enantiomeric excesses (> 98% ee). (c) 2007 Elsevier Ltd. All rights reserved.