The rational design of bis(oxazoline)-copper(II) catalysts based on postulated intramolecular secondary n-cation interaction for the highly enantioselective Diels-Alder reaction is presented. A theoretical calculation suggested that the n electrons of the 4,4'-sulfonamidomethyl groups successfully interact with the Cu(II) cation and that the counteranions with protons of sulfonamido groups. These secondary interactions might be essential for the high catalytic activity, the broad range of substrates, and the high level of induction of the enantioselectivity.
Chiral ditopic receptors. Application to palladium-catalyzed allylic alkylation
Chiral pyridinooxazoline, quinolinooxazoline, bis(oxazolino)pyridine (pybox), and bisoxazoline (box) derivatives containing crown ether residues were prepared. Some of the ligands were assessed in substrate binding studies and in palladium catalyzed allylic alkylations. (C) 2003 Elsevier Ltd. All rights reserved.
Preparation of<scp>l</scp>-Threoninol and Its Bisoxazoline Derivative
(R,R)-Threoninol was prepared in one step from L-threonine in 86% isolated yield. The product was regioselectively transformed into 2,2-bis[(4R,5R)-4-(hydroxymethyl)-5-methyl-1,3-oxazolin-2-yl]propane in 42% isolated yield.
The first 4,4′-imidazolium-tagged C<sub>2</sub>-symmetric bis(oxazolines): application in the asymmetric Henry reaction
Highly efficient and recyclable imidazolium-tagged bis(oxazolines), with an imidazolium tagged onto the 4,4′-position of the box, have been designed and prepared for the first time. They have been synthesized from dimethylmalonic acid and used as chiral ligands in the copper(II)-catalyzed classic asymmetric Henry reaction between aldehydes and nitromethane. A systematic analysis of the anions showed