He P, Li X, Zheng H, Li W, Lin L, Feng X * Sichuan University, Chengdu, P. R of China
Asymmetric 1,2-Reduction of Enones with Potassium Borohydride Catalyzed by Chiral
N,N′‑Dioxide–Scandium(III) Complexes.
Org. Lett. 2012;
14: 5134-5137
Key words
scandium - 1,2-reduction - chiral allylic alcohols - metal borohydrides
Significance
As an extension on previous work using chiral N,N′-dioxide–metal complexes for asymmetric catalysis (see Review), the authors now describe
the scandium-catalyzed asymmetric reaction of enones and ketones with KBH4. The resulting chiral alcohols are obtained with good yield and enantioselectivity.
Review
X. Liu, L. Lin, X. Feng Acc. Chem. Res. 2011, 44, 574–587.
Comment
Chiral allylic alcohols are important motifs widely present in natural products and
biologically active molecules. The enantioselective reduction of enones is known as
the most straight-forward access to such motifs. Herein, the first example of catalytic
enantioselective reduction of enones and ketones by using KBH4 is reported. The utilization of an aqueous solution of KBH4 was found to be crucial for obtaining high yield and enantioselectivity as the presence
of water is believed to benefit proton transfer to accelerate the catalytic cycle.
In this case, the reaction was performed in a homogeneous catalyst system. The HRMS
spectra experiments indicated that the initial reducing species is KBH3OH.
