New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated N,N ‘-Dialkylureas as Chiral Bases and Sterically Crowded Phosphines for Asymmetric Catalysis

The synthesis of new homochiral pseudo-C 2 -symmetrical ligands of type 1 bearing a nonstereogenic chirotopic center is reported. Two such structural units are combined in the ureas 2 and 10, which proved to be useful for enantioselective deprotonation and alkylation of ketones (up to 88% ee). The m...

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Bibliographic Details
Published in:Journal of organic chemistry 1999-07, Vol.64 (15), p.5581-5588
Main Authors: Graf, Claus-Dieter, Malan, Christophe, Harms, Klaus, Knochel, Paul
Format: Article
Language:English
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Summary:The synthesis of new homochiral pseudo-C 2 -symmetrical ligands of type 1 bearing a nonstereogenic chirotopic center is reported. Two such structural units are combined in the ureas 2 and 10, which proved to be useful for enantioselective deprotonation and alkylation of ketones (up to 88% ee). The monophosphine 3 induced a high enantiomeric excess in the Pd-catalyzed allylation of dimethyl malonate (up to 73% ee). Furthermore, we have shown that the achiral sterically crowded alkyl diphosphine 23 efficiently stabilized Pd(0) at high temperatures.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo990412u