Polymer-supported dichlorotitanium dialkoxide was readily prepared from polystyrene-bound α-glycol and dichlorotitanium diisopropoxide. When we employed it as an immobilized Lewisacidcatalyst, several fundamental and important Lewis acid-catalyzed reactions proceeded smoothly with fair chemical yields.
Yb(OTf)(3) with TMSCl or TMSOTf catalyzed an imino enereaction. The reaction of N-tosylbenzaldimine (1) with alpha-methylstyrene (2) proceeded smoothly to give homoallylic amine 3 in the presence of a catalytic amount of Yb(OTf)(3) and TMSCl. This catalytic system was successfully applied to the imino enereactions of various aldimines with alkenes. This new imino enereaction provides a unique method for
Yb(OTf)(3), can catalyze the glyoxylate-ene reaction effectively as a water-stable and reusable catalyst. Moreover, the selectivity of DA product or ene product can be adjusted by solvents in the reaction of glyoxylates with a diene (isoprene). In the presence of chiral ytterbium complexes generated in situ from Yb(OTf)(3) and optical 6,6'-disubstituted binaphthols, methyl glyoxylate smoothly reacts with alpha-methyl styrene to afford alpha-hydroxyl esters in modest optical yields. (C) 1997 Elsevier Science Ltd.
Synthesis of Novel Chiral Spiro Bis(pyrazole) Ligands
作者:Hiroaki Sasai、Shinobu Takizawa、Yuji Honda、Midori A. Arai、Takahiro Kato
DOI:10.3987/com-03-9874
日期:——
Vanadium-Catalyzed Asymmetric Oxidation of α-Hydroxy Esters Using Molecular Oxygen as Stoichiometric Oxidant
作者:Alexander T. Radosevich、Christine Musich、F. Dean Toste
DOI:10.1021/ja0433424
日期:2005.2.1
A vanadium-catalyzed method for the oxidative kinetic resolution of alpha-hydroxyesters, using oxygen as the terminal oxidant, is described. The catalyst is generated in situ from vanadium(V) tri-iso-propoxyoxide in combination with a tridentate ligand derived from 3,5-di-tert-butylsalicylaldehyde and (S)-tert-leucinol. The reaction allows for the enantioselectivesynthesis of both aromatic and aliphatic