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
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.
catalyze the enantioselective aldol reaction of aldehydes with ketene silyl acetals in DMF at roomtemperature. The platinum(II) complex-catalyzed the enantioselective aldol reaction of aldehydes with 1-methoxy-2-methyl-(1-trimethylsilyloxy)propene gave the corresponding aldols in high yields with enantioselectivity up to 92%. With 5 mol % loading of the complexes, the enantioselective aldol reaction of aldehydes
Lewis Base Activation of Lewis Acids: Catalytic, Enantioselective Addition of Silyl Ketene Acetals to Aldehydes
作者:Scott E. Denmark、Gregory L. Beutner、Thomas Wynn、Martin D. Eastgate
DOI:10.1021/ja047339w
日期:2005.3.1
The concept of Lewisbase activation of Lewisacids has been reduced to practice for catalysis of the aldolreaction of silyl ketene acetals and silyl dienol ethers with aldehydes. The weakly acidic species, silicon tetrachloride (SiCl4), can be activated by binding of a strongly Lewis basic chiral phosphoramide, leading to in situ formation of a chiral Lewisacid. This species has proven to be a competent
Siloxy Esters as Traceless Activators of Carboxylic Acids: Boron‐Catalyzed Chemoselective Asymmetric Aldol Reaction**
作者:Taiki Fujita、Mina Yamane、W. M. C. Sameera、Harunobu Mitsunuma、Motomu Kanai
DOI:10.1002/anie.202109788
日期:2021.11.8
We developed a chiral boron-catalyzed, carboxylic acid-selective asymmetric aldol reaction applicable to multifunctional substrates at late stages for the first time. Computational studies rationalized the reaction mechanism and stereoselectivity through Si/B enediolates acting as the active species.
supported on a modified poly(ethylene glycol) were shown to be effective Cu(II) ligands for the enantioselective Mukaiyama-aldol condensation of various aldehydes with the trimethylsilyl keteneacetal of methyl isobutyrate carried out in water. Enantiomeric excesses comparable to those obtained with nonsupported ligands in the same solvent were observed. The solubility of the ligand in water, ensured by