A highly stereoselective trichlorosilane-mediated reduction of N-benzyl enamines was developed; the combination of a low cost, easy to make metal-free catalyst and an inexpensive chiral auxiliary allowed to perform the reaction on substrates with different structural features often with total control of the stereoselectivity. By easy deprotection through hydrogenolysis followed by conversion of β-aminoester
The external chiral ligand-controlled asymmetric conjugateaddition reaction of lithium amides with alpha,beta-unsaturated esters provided beta-amino esters in high yields and high enantioselectivities.
Asymmetric Synthesis of Intermediates for Otamixaban and Premafloxacin by the Chiral Ligand-Controlled Asymmetric Conjugate Addition of a Lithium Amide
作者:Takeo Sakai、Yoshito Kawamoto、Kiyoshi Tomioka
DOI:10.1021/jo060588d
日期:2006.6.1
A chiral ligand-controlled conjugateaddition reaction of lithium benzyl(trimethylsilyl)amide with tert-butyl enoates gave the corresponding lithium enolates that were then treated with electrophiles, giving anti-alkylation products with high ee up to 98%. The benzyl group on the amino nitrogen was removed by the oxidation of secondary amines to imines and subsequent transoximation to give 3-aminoalkanoates
Chiral Lewis Base Catalyzed Highly Enantioselective Reduction of N-Alkyl β-Enamino Esters with Trichlorosilane and Water
作者:Xinjun Wu、Yang Li、Chao Wang、Li Zhou、Xiaoxia Lu、Jian Sun
DOI:10.1002/chem.201003105
日期:2011.3.1
of a chiral Lewisbase catalyst 2, the supposedly moisture‐unfriendly reduction system with trichlorosilane was found to be highly efficient and enantioselective when using water as an additive. For the first time, this method enables the reduction of a broad range of N‐alkyl β‐enamino esters 1 to give N‐alkyl β‐amino esters 3 in good to high yields and with excellent enantioselectivities (see scheme)
Chiral ligand-controlled asymmetric conjugate amination of enoates with lithium mesitylmethyl(trimethylsilyl)amide
作者:Takeo Sakai、Hirohisa Doi、Kiyoshi Tomioka
DOI:10.1016/j.tet.2006.06.040
日期:2006.8
Lithium mesitylmethyl(trimethylsilyl)amide behaved as a nice amination agent in a chiral ligand-controlled conjugate addition reaction of tert-butyl cinnamate to give the conjugate amination product with 99% ee in 90% yield. Other acyclic and cyclic enoates were also aminated in reasonably high enantioselectivity, while the deprotonation of abstractable proton of enoates caused yield loss of the conjugate amination products, due to the bulkiness and enriched basicity of the lithium amide. Although such steric bulkiness made hard the hydrogenolytic cleavage of a mesitylmethyl-N bond of the adducts, a new protocol comprising N-chlorination-regioselective dehydro-chlorination-transoximation was developed for N-dearylmethylation, giving 3-aminoalkanoates in reasonably good yields. (c) 2006 Elsevier Ltd. All rights reserved.