新手性配体(QN)2AQN的合成及其催化肉桂酸甲酯的不对称氨羟化反应研究

在AlCl₃和多聚磷酸的存在下, 以邻苯二甲酸酐和对二氟苯为原料, 通过Friedel-Crafts和环化反应, 用改进的方法以60%的产率生成1,4-二氟蒽醌. 然后通过奎宁锂与1,4-二氟蒽醌的亲核取代反应得到新型手性配体(QN)₂AQN, 产率85%. 在氧化-供氮试剂N-氯代氨基甲酸苄酯存在下, (QN)₂AQN与OsO₄原位生成的催化剂在五种肉桂酸甲酯的不对称氨羟化反应中表现出优异的对映选择性(90%～96% ee)和一般至优秀的区域选择性(75∶25～98∶2), 产率50%～70%, 高于文献报道的结果. 该手性配体易于合成, 成本低廉, 用于催化不对称氨羟化反应, 可以制备光学活性的α-氨基酸酯类化合物.

Synthesis of a New Chiral Ligand (QN)2AQN and Its Application to the Catalytic Asymmetric Aminohydroxylation of Methyl Cinnamates

1,4-Difluoroanthraquinone was obtained in 60% yield by Friedel-Crafts reaction of phthalic anhydride and 1,4-difluorobenzene in the presence of AlCl₃ followed by cyclization with polyphosphoric acid. Then the ligand (QN)₂AQN was prepared by nucleophilic substitution of 1,4-difluoroanthraquinone with the lithium salt of quinine in 85% yield. In the presence of benzyl N-chlorocarbamate (the oxidant and nitrogen source), five methyl cinnamates gave the vicinal amino alcohols via asymmetric aminohydroxylation (AA) catalyzed by (QN)₂AQN-OsO₄ complex in excellent enantioselectivities of 90%～96% ee, normal to high regioselectivities of 75∶25～98∶2 and good yields of 50%～70%. These results were comparable to those of the best catalyst reported for AA reaction. Due to the easy preparation and low cost, this new chiral ligand was applied to the catalytic asymmetric aminohydroxylation to produce enantioselective α-aminoacid esters.