Polydentate chiral heteroorganic ligands/catalysts—impact of particular functional groups on their activity in selected reactions of asymmetric synthesis
摘要:
The influence of each functional group in enantiomerically pure ligands 1, bearing a hydroxy moiety, a stereogenic sulfinyl group and an enantiomeric amine moiety, on ligand catalytic efficiency in enantioselective nitroaldol (Henry) reactions was investigated by subsequent transformation and/or protection of these groups. It was found that, although the absolute configuration of the amine moiety exerted a decisive influence on the stereochemical outcome of the reaction, the presence of the sulfinyl group was crucial. The hydroxy group could be replaced by a second enantiomeric amine moiety, but in order to achieve high catalytic activity of the ligand, it was necessary to retain the sulfinyl moiety in its molecule. This clearly indicated that the simultaneous presence of three coordinating centres was essential for the efficiency of the catalysts and allowed us to conclude that the original ligands 1 demonstrated a tridentate character. (C) 2013 Elsevier Ltd. All rights reserved.
Highly enantioselective Henry reaction catalyzed by chiral tridentate heteroorganic ligands
摘要:
New tridentate enantiomerically pure heteroatom catalysts, containing hydroxyl, sulfinyl and amino groups, proved to be highly efficient in the enantioselective nitroaldol (Henry) reaction to give the desired adducts in very high yields (Lip to 90%) and with ees up to 98%. The influence of the stereogenic centres located on the sulfinyl sulfur atom and in the amine moiety is also discussed. (C) 2009 Elsevier Ltd. All rights reserved.