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.
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.