SpinPHOX/Ir(Ⅰ)催化的2-羟甲基-3-芳基丙烯酸的不对称氢化

SpinPHOX/Ir(I) Catalyzed Asymmetric Hydrogenation of(E)-2-(hydroxymethyl)-3-Arylacrylic Acids

光学活性的2-羟甲基-3-芳基丙酸类化合物是许多手性药物的关键合成中间体,但到目前为止其不对称合成方法大多存在对映选择性不高及/或底物范围有限等问题.报道了手性SpinPHOX/Ir(I)络合物在一系列2-羟甲基-3-芳基丙烯酸的不对称氢化中表现出优良的催化性能,取得完全的底物转化和良好到优秀的对映选择性(高达95%ee).对于同一2-羟甲基-3-芳基丙烯酸底物的不对称氢化,使用中心手性相同但螺环骨架上的轴手性相反的催化剂分别以优良的对映选择性获得构型相反的产物,从而为光学活性2-羟甲基-3-芳基丙酸及相关手性药物的不对称合成提供了一条简便高效的途径.

Optically active 3-aryl-2-hydroxymethylpropionoic acids are highly useful chiral building blocks for the preparation of some drugs, but so far their asymmetric syntheses are still plagued by modest enantioselectivity and/or limited substrate scope. In the present study, the SpinPHOX/Ir(I) complexes(S,S)-1c and(R,S)-1e have been demonstrated to be highly effective for the asymmetric hydrogenation of(E)-2-(hydroxymethyl)-3-arylacrylic acids, affording the corresponding optically active 3-aryl-2-hydroxymethylpropionoic acids in good to excellent enantiopurities(ee up to 95%). Catalyst screening and reaction optimization with(E)-2-(hydroxymethyl)-3-phenylacrylic acid 2a as the model substrate, revealed that the asymmetric hydrogenation was best conducted in dichloromethane at r.t. under 10 atm of hydrogen with(S,S)-1c as the catalyst, and the presence of 1 equiv. of a suitable organic base(such as triethylamine) was essential for full substrate conversion and excellent product enantioselectivity(94% ee). Evaluation of the substrate scope of the protocol was performed using various 2-hydroxymethyl cinnamic acid derivatives 2a^2n with various substituents on the phenyl group. Full conversions and good to high ee values were obtained in most cases, irrespective of the electron-withdrawing or-donating nature of the substituent. Using complex(R,S)-1e as the catalyst under a slightly modified reaction conditions(50 atm H2, 40 ℃), several substrates were hydrogenated in excellent ee values but with the sense of chiral induction opposite to those obtained by using(S,S)-1c. The reaction can be readily scaled up to gram-scale with retention of enantioselectivity. Among the optically enriched hydrogenation products obtained from this procedure,(S)-3a,(R)-3a and(-)-3n can be used as chiral building blocks for the asymmetric synthesis of pharmaceuticals Alvimopan, Ecadotril, and Fasidotril, respectively. Using this protocol, various(E)-2-(hydroxymethyl)-3-arylacrylic acids could be readily hydrogenated in high optical purities, thus providing a facile access to both enantiomers of the chiral 3-aryl-2-hydroxymethylpropionoic acids as well as the relevant chiral drugs.