Planar- and central-chiral N,O-[2.2]paracyclophane ligands: Non-linear-like effects and activity
The non-linear-like effect (NLLE), activity, temperature dependence, and kinetics of hydroxy-[2.2]paracyclophane ketimine ligands have been investigated with the 1,2-addition reaction of diethylzinc to cyclohexanecarbaldehyde. A linear correlation between the enantiomeric excess of AHPC ketimine ligands bearing a phenylethyl side group and the product was observed with 0.5 mol% of catalyst loading. On increasing the catalyst loading to 4 mol%, a precipitate of the inactive heterochiral species was formed and resulted in a positive non-linear-like effect. The enantiomeric ratio was found to have linear temperature dependence.
Lauterwasser, Frank,Vanderheiden, Sylvia,Braese, Stefan
Catalysts for asymmetric addition of organozinc reagents to aldehydes and method for preparation
Novel chiral aminoalcohol catalysts and methods for their preparation are provided. The first catalyst is prepared via selective hydrogenation of one of two benzene rings in a precursor. The aminoalcohol promotes the asymmetric addition of organozinc reagents to aldehydes to afford optically active alcohols or their esters. The second catalyst is prepared by selective dialkylation of 3-exo-aminoisoborneol with a 2-haloethyl ether. The aminoalcohol promotes the addition of organozinc reagents to aliphatic aldehydes containing a β-branch with greatly enhanced enantioselectivity relative to DAIB.
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(2008/06/13)
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