A unique binary chiral phosphoric acid 1a/MgF2 catalyst that enables effective catalysis of asymmetric Friedel−Craftsreactions of phenols with up to 82% yield and >99% ee is presented. A dramatic synergistic effect has been observed in the combinations of two types of acids, wherein a highly active binary-acid catalyst can be generated from two individually inert acids.
Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate
作者:Jian Lv、Qichao Zhang、Xingren Zhong、Sanzhong Luo
DOI:10.1021/jacs.5b11085
日期:2015.12.16
Stable carbocations such as tritylium ions have been widely explored as organic Lewisacid catalysts and reagents in organic synthesis. However, achieving asymmetric carbocation catalysis remains elusive ever since they were first identified over one century ago. The challenges mainly come from their limited compatibility, scarcity of chiral carbocations, as well as the extremely low barrier to racemization
exchange of the metal ion from Zr(IV) to Fe(III) leads to a switch in the enantioselectivity of binary acid-catalyzed conjugate hydride reductions. In the presence of Hantzsch ester, γ-indolyl β,γ-unsaturated α-keto esters could be reduced to the desired (S)- or (R)-products, respectively, with good to excellent enantioselectivity (up to 98% ee).
金属离子从 Zr(IV) 到 Fe(III) 的交换导致二元酸催化的共轭氢化物还原的对映选择性发生变化。在 Hantzsch 酯存在下,γ-吲哚基 β,γ-不饱和 α-酮酯可以分别还原为所需的 ( S )- 或 ( R )- 产物,具有良好至优异的对映选择性(高达 98% ee) .