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Temperature‐dependent nonlinear effects and catalyst evolution in the asymmetric addition of diethylzinc to benzaldehyde
Author(s) -
Balsells Jaume,
Costa Anna M.,
Walsh Patrick J.
Publication year - 2002
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1560/lm1c-rrq5-12aj-njjc
Subject(s) - enantiopure drug , chemistry , diethylzinc , alkoxide , enantioselective synthesis , catalysis , benzaldehyde , titanium , ligand (biochemistry) , alkyl , combinatorial chemistry , organic chemistry , receptor , biochemistry
Several efficient and highly enantioselective titanium‐based catalysts promote the asymmetric addition of alkyl groups to aldehydes. The catalysts involved in these reactions have been found not to exhibit nonlinear behavior. We have been able to identify a series of chiral bis(sulfonamide)‐based titanium catalysts that do show nonlinear behavior. Monitoring of the product ee's (ee p 's) at different conversions and different temperatures has led us to propose that nonlinear behavior is caused by an autoinduction process rather than by catalyst aggregation. Evidence to support this hypothesis includes ee p 's that change with the extent of conversion. We have found that when enantiopure ligand was used, the ee p increases with conversion from 72% to 80%. However, use of non‐enantiopure ligand results in ee p 's that decrease with conversion. These results are rationalized by different rates of alkoxide exchange processes between like and unlike titanium‐alkoxide containing complexes.