The addition of Et2Zn on benzaldehyde in the presence of a stoichiometric amount of Ti(Oi-Pr)4 ca... more The addition of Et2Zn on benzaldehyde in the presence of a stoichiometric amount of Ti(Oi-Pr)4 catalysed by (1R,2R)-bis(trifluoromethanesulfonamido)-cyclohexane 1a has been revisited. A nonlinear effect was present or absent, depending on the catalyst preparation. An asymmetric amplification has been observed when Ti(Oi-Pr)4 was added to 1a followed by Et2Zn and then benzaldehyde (Ohno procedure). In the alternate procedure (Walsh), where
ABSTRACT Kinetic resolutions with enantioimpure chiral auxiliaries (reagents or catalysts) are co... more ABSTRACT Kinetic resolutions with enantioimpure chiral auxiliaries (reagents or catalysts) are considered, and a kinetic treatment for various rate laws is described. A useful parameter, the apparent stereoselectivity factor, is defined and correlated to the enantiomeric excess of the chiral auxiliary. Deviations from the regular laws are possible (asymmetric amplification or depletion). These anomalies have their origins in the same phenomena that cause nonlinear effects in enantioselective catalysis. Asymmetric amplifications have been experimentally observed.
The addition of Et2Zn on benzaldehyde in the presence of a stoichiometric amount of Ti(Oi-Pr)4 ca... more The addition of Et2Zn on benzaldehyde in the presence of a stoichiometric amount of Ti(Oi-Pr)4 catalysed by (1R,2R)-bis(trifluoromethanesulfonamido)-cyclohexane 1a has been revisited. A nonlinear effect was present or absent, depending on the catalyst preparation. An asymmetric amplification has been observed when Ti(Oi-Pr)4 was added to 1a followed by Et2Zn and then benzaldehyde (Ohno procedure). In the alternate procedure (Walsh), where
ABSTRACT Kinetic resolutions with enantioimpure chiral auxiliaries (reagents or catalysts) are co... more ABSTRACT Kinetic resolutions with enantioimpure chiral auxiliaries (reagents or catalysts) are considered, and a kinetic treatment for various rate laws is described. A useful parameter, the apparent stereoselectivity factor, is defined and correlated to the enantiomeric excess of the chiral auxiliary. Deviations from the regular laws are possible (asymmetric amplification or depletion). These anomalies have their origins in the same phenomena that cause nonlinear effects in enantioselective catalysis. Asymmetric amplifications have been experimentally observed.
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Papers by David Fenwick