Asymmetric induction in kinetically controlled zirconium‐catalysed Meerwein‐Ponndorf‐Verley reductions

Twelve chiral ligands 718 were tested in the new kinetically controlled variation of zirconium alkoxide catalysed Meerwein‐Ponndorf‐Verley reduction of 2′‐chloroacetophenone (2) using rac‐4 as the reducing alcohol (Scheme 3). The tetraaryl‐1,3‐dioxolanes 11 (ca. 30% enantiomeric excess, ee) and the triphenylethanediol 14 (62% ee, 99% yield) gave the best results. A relatively low dependence on the amount of the catalyst (aluminum alkoxide gave no asymmetric induction) and the ligand excess was observed compared with a very high dependence on incubation time of Zr(OtBu)4 with the chiral ligand 14 and also on the reaction temperature.