Highly <i>anti</i>-Selective Asymmetric Aldol Reactions Using Chiral Zirconium Catalysts. Improvement of Activities, Structure of the Novel Zirconium Complexes, and Effect of a Small Amount of Water for the Preparation of the Catalysts
作者:Yasuhiro Yamashita、Haruro Ishitani、Haruka Shimizu、Shū Kobayashi
DOI:10.1021/ja016293t
日期:2002.4.1
reactions) have been performed using novel chiral zirconium catalysts. The reactions proceeded in high yields under mild conditions, and anti-adducts were obtained in high diastereo- and enantioselectivities. The catalysts were first prepared from zirconium(IV) tert-butoxide (Zr(O(t)Bu)(4)), (R)-3,3'-diiodo-1,1'-binaphthalene-2,2'-diol ((R)-3,3'-I(2)BINOL), a primary alcohol, and a small amount of water.
甲硅烷基烯醇醚与醛的催化不对称醛醇反应(Mukaiyama 醛醇反应)已使用新型手性锆催化剂进行。反应在温和条件下以高产率进行,并以高非对映选择性和对映选择性获得抗加合物。该催化剂首先由叔丁醇锆 (IV) (Zr(O(t)Bu)(4)), (R)-3,3'-diiodo-1,1'-binaphthalene-2,2'-二醇 ((R)-3,3'-I(2)BINOL)、伯醇和少量水。结果表明,伯醇在完成催化循环中起着重要作用,少量的水对于获得高选择性至关重要。此外,手性锆催化剂的活性通过使用新的配体 (R)-3,3'-I(2)-6,6'-X(2)BINOL (X = Br, I, C(2) F(5)), 并且已经表明,使用新型锆催化剂,即使是反应性较低的底物的羟醛反应也能顺利进行。最后,对这些催化剂进行了核磁共振研究,这表明催化剂会形成二聚体结构,水会影响催化剂的形成。