具有C2对称的氮磷-氧磷配体双噁唑啉磷乙烷的合成及在不对称催化加氢中的应用

利用易得的光学纯N-甲基氨基醇与1,2-双(二氯磷)乙烷缩合合成了一类新的具有C₂对称轴的氮磷-氧磷配体(R,R)-双噁唑啉磷乙烷(BOAPE) 1～4. 该类配体不仅具有C₂对称结构和刚性五元环, 还具有富电子特性, 利用500 MHz进行了¹H NMR, ³¹P NMR, ¹³C NMR表征. 与这些配体配位形成的Rh配合物用于N-苯甲酰基脱氢丙氨酸衍生物和α-功能化酮不对称加氢, 分别可以得到99%和98%的ee. 这类配体比它们相对应的非C₂对称的氮磷-氧磷化合物(AMPP)配体具有更高的对映选择性. 在这四个新的配体中配体(R,R)-Ph-BOAPE (2)的催化性能最优. 催化剂[Rh(COD)(R,R)-Ph-BOAPE]BF₄的半反应周期t_1/2和周转频率(TOF)在N-苯甲酰基肉桂酸甲酯的不对称加氢反应中分别为12 min和6.5 min^－1.

Synthesis of Aminophosphine Phosphinite Ligand Bis(oxazaphospholano)-ethane with C2-Symmetric Axis and Its Application in Asymmetric Hydrogenation

A new class of C₂-symmetric (R,R)-bis(oxazaphospholano)ethane (BOAPE) 1～4 was synthesized by the condensation reaction of readily available optically active amino alcohols with 1,2-bis(dichlorophosphino)ethane. These new ligands bear not only C₂-symmetry axis but also a rigid ring. They were characterized by ¹H NMR, ³¹P NMR and ¹³C NMR spectra. The enantioselective yields were obtained by Rh complex catalyzed asymmetric catalytic hydrogenation of N-benzoyldehydroamino acid derivatives and α-functionalized ketones in up to 99% ee and 98% ee, respectively. This new class of (R,R)-BOAPE gave much higher efficiency and enantionselectivity than their corresponding non C₂-asymmetric aminophosphine phosphinite (AMPP). Among these ligands, (R,R)-Ph-BOAPE (2) was the best one. The t_1/2 and turnover of frequency (TOF) of the catalyst [Rh(COD)(R,R)-Ph-BOAPE]BF₄ for the asymmetric hydrogenation of methyl N-benzoyl cinnamate were 12 min and 6.5 min^－1, respectively.