Highly enantioselective direct Michael addition of 1,3-dicarbonyl compounds to β-fluoroalkyl-α-nitroalkenes
作者:Yan Zhao、Xiao-Jin Wang、Yun Lin、Chen-Xin Cai、Jin-Tao Liu
DOI:10.1016/j.tet.2014.02.062
日期:2014.4
Cinchona alkaloid catalysts were used in the Michaeladdition reaction of 1,3-dicarbonylcompounds to β-fluoroalkyl-α-nitroalkenes for the first time. The catalytic system performed well over a broad scope of substrates including β-keto esters and 1,3-diketones with high diastereoselectivities and excellent enantioselectivities (up to 99% ee) under mild conditions. A wide range of useful fluorinated
asymmetric cycloaddition reaction of fluoromethyl-substituted nitroalkenes with azomethine ylides was developed using a catalyst derived from copper(I) perchlorate and a commercially available, chiral Walphos ligand. This method provides a simple approach to optically active exo-3-(fluoromethyl)proline derivatives in high yields, as well as in high diastereo- and enantioselectivities. 1,3-dipolar cycloaddition
Synthesis of Ψ[CH(RF)NH]Gly-peptides: The dramatic effect of a single fluorine atom on the diastereocontrol of the key aza-Michael reaction
作者:Serena Bigotti、Stefano V. Meille、Alessandro Volonterio、Matteo Zanda
DOI:10.1016/j.jfluchem.2008.06.018
日期:2008.9
We describe in full-detail the synthesis of new Psi[CH(R-F)NH]-peptidomimetics, having different fluoroalkyl groups RF, as peptide bond surrogates. A key step in the synthesis is a stereoselective aza-Michael addition of chiral alpha-amino acid esters to beta-fluoroalkyl-alpha-nitroethenes. The diastereoselection of the process was influenced by the electronegativity, rather than by the steric bulk, of the fluorinated residue R-F in the beta-position of the nitroalkene acceptors. Replacement of a single F atom of R-F by a hydrogen or methyl group brings about a dramatic drop of stereocontrol, whereas Br, Cl and CF3, albeit bulkier than F, provide inferior results in terms of stereocontrol. A mechanistic hypothesis is provided. (c) 2008 Elsevier B.V. All rights reserved.