关键词: 不对称催化, 手性氮氧金属络合物, ene 反应, 高烯丙基醇, 镍

The optically active homoallylic alcohols are widespread in natural products and have been frequently used as convenient building blocks in organic synthesis. As one of the most efficient synthetic methods to obtain chiral homoallylic alcohols, the asymmetric ene reaction of carbonyl compounds has attracted significant attentions. N,N'-dioxide-amide compounds, which could be easily prepared from chiral amino acids, have been developed into a type of privileged ligand and organocatalyst in various asymmetric reactions. On the other hand, the fluoroorganic compounds are important building blocks for the total synthesis of complex natural products, pharmaceuticals, and plant pesticides due to the unique abilities of the fluorine atom to significantly modify their physicochemical and biological properties. In recent years, the interest of the pharmaceutical industry in trifluoromethyl-containing compounds has grown significantly. In this manuscript, a series of Ni(II)-N,N'-dioxide complexes have been investigated for the asymmetric carbonyl-ene reaction of ethyl trifluoropyruvate. It was found that the electronic and steric characteristics of substituents on the amide moieties of the ligand greatly affected the reaction outcomes. The catalyst L4 with bulky and electron-donating groups at the ortho positions of aniline generated perfect stereoinductive environment. And a wide range of alkenes, including aromatic and aliphatic alkenes, tolerated the reaction well under mild reaction conditions, giving the corresponding trifluoromethyl-substituted allyl alcohols in excellent enantioselectivities (in the range of 97%～＞99% ee) with high yields (up to 96%). Furthermore, the X-ray structure of the ligand L4 and the catalyst L4-Ni(II) complex shed light on the stereocontrol of the reaction. A possible transition state has been proposed to explain the origin of activation and asymmetric inductivity.

Key words: asymmetric catalysis, chiral N,N'-dioxide-metal complexes, ene reaction, homoallylic alcohols, nickel